Realistic Energy Weaponry
Christian Thalmann
I seem to recall having witnessed a discussion about laser
on this newsgroup, maybe a year or so ago. Does anyone know
a website where the essentials of realistic laser, plasma etc
weaponry can be found? Or, should that fail, is there an
archive for this newsgroup where I could try to dig the stuff
up again?
I'd be particularly interested in the formula for the relation
of beam diameter, emitter diameter and wavelength for a laser;
energy requirements for effects similar to a rifle bullet;
necessary resonator/emitter design features, and the likes.
As for plasma weaponry: How far could a plasma bolt travel
without dissipating? Would it just explode immediately once
out of the barrel, no matter the circumstances? Could a
"smoke-ring" style plasma projectile survive longer? What
about ion beams: What's the behavior of relativistic ions
among each other? How quickly does the beam decay due to
EM repulsion? How do you estimate the performance vs armor?
Other stuff: Coherent matter beams, gravitic beams, launched
miniature black holes -- too whacky to comment?
Such scientific considerations, compiled in a website, would
be a nice addition to this nifty sci-fi science FAQ you have
here.
-- Christian Thalmann
cinga (at) gmx (dot) net
http://catharsis.netpeople.ch/
Erik Max Francis
> I'd be particularly interested in the formula for the relation
> of beam diameter, emitter diameter and wavelength for a laser;
> energy requirements for effects similar to a rifle bullet;
> necessary resonator/emitter design features, and the likes.
If you mean the beam spread relation for large distances, I've mentioned
it multiple times and used it for calculations; check Google Groups.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ To be a man means to be a fellow man.
\__/ Leo Baeck
Christian Thalmann
> As far as Coherent matter beams go, the military has had some success
> with weapons that use Fermi exclusion forces to accelerate a "pulse" of
> Quantum-entangled baryons and leptons.
Wow! Sounds thrilling. Though you probably mean the *Pauli*
exclusion principle. ;-) Got a website for that?
-- Christian Thalmann
Brian Trosko
> As far as Coherent matter beams go, the military has had some success
> with weapons that use Fermi exclusion forces to accelerate a "pulse" of
> Quantum-entangled baryons and leptons.
You mean guns firing bullets?
Karl M Syring
Stephan Aspridis
> As far as Coherent matter beams go, the military has had some success
> with weapons that use Fermi exclusion forces to accelerate a "pulse" of
> Quantum-entangled baryons and leptons.
>
You are evil and you know it ;-))))
Robert J. Kolker
Christian Thalmann wrote:
>
> Other stuff: Coherent matter beams, gravitic beams, launched
> miniature black holes -- too whacky to comment?
Yes. First of all gravity is a very weak force. A gravity wave has a
very low energy density. I alread own a coherent matter emitting weapon.
It is called a rifle. There is not enough energy in the entire solar
system to make a small black hole.
The most cost-efficient energy weapon ever invented is a kinetic energy
kill weapon. That includes bullets, artillery shells and dropping rocks
on your enemy.
Bob Kolker
Robert J. Kolker
Paul Ciszek wrote:
> As far as Coherent matter beams go, the military has had some success
> with weapons that use Fermi exclusion forces to accelerate a "pulse" of
> Quantum-entangled baryons and leptons.
Citation please.
Bob Kolker
Erik Max Francis
> Yes. First of all gravity is a very weak force. A gravity wave has a
> very low energy density. I alread own a coherent matter emitting
> weapon.
> It is called a rifle. There is not enough energy in the entire solar
> system to make a small black hole.
The amount of energy released by a primordial black hole evaporating is
much less than the energy released by the Sun every second, so this
statement is clearly untrue.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ In Heaven all the interesting people are missing.
\__/ Friedrich Nietzsche
Brian Trosko
David Duffy
> Hi everyone.
> I seem to recall having witnessed a discussion about laser
> on this newsgroup, maybe a year or so ago. Does anyone know
> a website where the essentials of realistic laser, plasma etc
> weaponry can be found? Or, should that fail, is there an
> archive for this newsgroup where I could try to dig the stuff
> up again?
Folks may be interested in July 4th Science 301: 54-55, 61-64
describing the Teramobile. Fig 4 shows "laser filaments"
guiding straight high voltage electrical discharges, looking
suspiciously like light sabre blades. "Pulses with energy
above 10 mJ undergo self-focussing collapse in air and
produce a highly intense light filament with a diameter of
100 um and a length of several metres". And finally,
"Under appropriate conditions, a higher order nonlinearity
such as plasma formation may stabilize the collapse - with
the tantalizing possibility of the pulse formation of an 'optical
bullet' that neither diffracts in space nor disperses in time."
--
| David Duffy (MBBS PhD) ,-_|\
| email: dav...@qimr.edu.au ph: INT+61+7+3362-0217 fax: -0101 / *
| Epidemiology Unit, Queensland Institute of Medical Research \_,-._/
| 300 Herston Rd, Brisbane, Queensland 4029, Australia GPG 4D0B994A v
George William Herbert
>Christian Thalmann wrote:
>> I'd be particularly interested in the formula for the relation
>> of beam diameter, emitter diameter and wavelength for a laser;
>
>If you mean the beam spread relation for large distances, I've mentioned
>it multiple times and used it for calculations; check Google Groups.
It's a lot easier if people know what keywords 8-)
"rayleigh range"
-george william herbert
gher...@retro.com
Christian Thalmann
Indeed. I meant coherent as in phase-locked, not condensed.
Atom-lasers. Bose-Einstein beams.
-- Christian Thalmann
MikeyD
> kill weapon. That includes bullets, artillery shells and dropping rocks
> on your enemy.
>
rifle.
John H
"MikeyD" <m_don...@hotmail.com> wrote in message
news:106270533...@iris.uk.clara.net...
Woudn't this depend on how many people you can pack into a city? How do
you reconcile nuking one lone dude in the middle of the desert with just
sniping him?
George William Herbert
If you include the overhead of the infantry training and manning
and other equipment, yes. As a rough order of magnitude cost,
Minuteman-III ICBMs cost about $25 million each, plus another $5
million or so for their 3 warhead packages, each of which will
probably kill no more than a quarter million people at most,
if targeted on cities.
In rough numbers, rifles are $550 including the new rail kits
and all, rifle ammo is $0.25/shot or less, but infantrymen cost
about $35k/yr including salary, overhead, training etc.
-george william herbert
gher...@retro.com
Luke
> Hi everyone.
>
>
> I seem to recall having witnessed a discussion about laser
> on this newsgroup, maybe a year or so ago. Does anyone know
> a website where the essentials of realistic laser, plasma etc
> weaponry can be found? Or, should that fail, is there an
> archive for this newsgroup where I could try to dig the stuff
> up again?
I have written many posts on this subject which can probably be found
by searching Google Groups.
>
> I'd be particularly interested in the formula for the relation
> of beam diameter, emitter diameter and wavelength for a laser;
Roughly, beam diameter = distance * wavelength / aperture diameter,
with some constants of order unity depending on the initial intensity
distribution across the aperture.
> energy requirements for effects similar to a rifle bullet;
> necessary resonator/emitter design features, and the likes.
This depends greatly on the nature of the laser beam. For continuous
lasers, forget about using it as a weapon against people by burning
holes in them. If it is too high powered, it will be blocked by its
own smoke and debris, so expect to take a couple seconds to burn a
hole through your enemy to reach his vital organs. Now you just need
to get him to sit absolutely still while the beam is doing its work,
while you hold the beam absolutely steady.
Continuous lasers might work better against people if employed as long
range flame throwers - give third degree burns to exposed skin, second
degree burns under light clothing, and ignite cloth for only about a
megajoule per square meter. Burns over your target's front torso,
arms, and face, plus burning hair and clothing, will likely be
immediately incapacitating (especially since he is now blind) and
ultimately lethal.
A single nanosecond pulse will cause a surface explosion. Pack on the
order of 10 to 100 kilojoules into the pulse for a blast big enough to
cause lethal internal trauma, disable limbs, and the like.
A train of nanosecond or sub-nanosecond pulses delivered about a
microsecond apart and lasting for a total time of around a millisecond
might be able to drill a deep hole into tissue with the subsequent
blasts, with effects similar to that of a modern bullet, all for about
a kilojoule in energy. If it works. No one knows if it does (or if
they do, they're not telling).
> As for plasma weaponry: How far could a plasma bolt travel
> without dissipating?
If it is near atmospheric pressure, you might be able to get it to
travel some distance in a jet or ring vortex or some more exotic
method such as ball lightning. I just doubt that a plasma at
atmospheric pressure would do much in a short period of time. The
energy of a gas (including the thermal energy), after all, is its
pressure times its volume (heat it up, and it either increases its
pressure or increases its volume). At atmospheric pressure, you'd
need a cubic meter of plasma to contain a kilojoule of energy. This
seems like rather a lot to be throwing around, and it is only going to
cause surface burns.
I can't think of any way to keep a plasma at significantly greater
than atmospheric pressure from exploding as soon as it is no longer
confined by your weapon, nor have I been able to come across any
literature describing way of doing so.
> What
> about ion beams: What's the behavior of relativistic ions
> among each other?
You can certainly get deadly beams of high energy ions or subatomic
particles. There are, however, some problems with these ideas.
First, most particles are either very difficult to generate (forget
working with mesons or other exotics) or have a very short range in
air (such as ions and protons) or are difficult to accelerate, focus,
and steer (such as neutrons). Basically, this leaves you with
electrons if you are in an atomsphere, which would probably work okay.
The other problem is that you are dealing with a beam of ionizing
radiation. Some of this radiation (the electrons, say) will be
scattering off of air molecules. Some of it will be scattering back
at you. Shoot your particle beam gun in an atmosphere, and you will
be taking radiation doses well above OSHA guidelines. You might be
okay with a few shots, but if you practiced regularly with your weapon
or if you were in a pitched battle -- hello radiation sickness.
Incidently, a hit anywhere on the body by a particle beam potent
enough to cause physical damage will pretty much ensure you've just
taken a lethal dose of radiation. You might survive the immediate
injury from hole it puts through you, so you'll have time to write
your will and say goodbye to your loved ones. That is, unless you
take enough radiation that your brain cells start dying, in which case
you've got a few minutes of consciousness left.
Also incidently, beams of x-rays or gamma rays are also beams of
ionizing radiation, with the same problems.
> How quickly does the beam decay due to
> EM repulsion?
In vacuum, the repulsion is large enough that in order to hit anything
worth shooting at (another spacecraft or satelitte or incoming warhead
or whatever) you will want to use a neutral particle beam. Accelerate
up a normal charged particle beam of protons or ions, then let it
recombine with electrons for particles that are electrically neutral
but still going really really fast. Now they wil not repell each
other or be deflected by planetary or stelar magnetic fields.
Unfortunately, neutralizing the beam in this way adds a random kick to
each particle depending on the details of just how it recombines with
the electron - thus dispersing the beam. It is a whole lot better
than a charged beam, but most lasers would focus even better.
In atmosphere, electron beams seem to be self-focusing, so you can get
around the mutual repulsion of the electrons. My guess is that they
are still deflected by the earth's magnetic field, though.
> How do you estimate the performance vs armor?
There are two things to worry about. First, high energy particles can
pass through some distance of matter without stopping, so some types
of particle beams will just pass through armor regardless (of course,
they will then tend to just pass through your target, too, without
making too much of a mess). Charged particles (and even neutralized
atoms will break up into charged particles after impacting a target)
tend to lose energy continuously as they pass though matter through
ionization of atoms along their path, and thus travel a certain,
specified range into the target (given by a number I've always called
the column density given as mass per unit area - divide by the
material's density to find how far the particle will travel in it).
This range varies depending on the charge, mass, and energy of the
particle in question - about 0.0003 g/cm^2 for electrons at 10 KeV,
about 5 g/cm^2 for electrons at 10 MeV. Note that all the air in
front of the target also acts as extra mass that the particles have to
penetrate, so the 10 MeV electron beam will only go through about 5
meters of air.
If the armor stops the particles, the thermal effects of the beam can
still burn through the armor, or the mechanical blast effects of a
short pulse beam can still break a hole in the armor.
Luke
Paul F. Dietz
> I can't think of any way to keep a plasma at significantly greater
> than atmospheric pressure from exploding as soon as it is no longer
> confined by your weapon, nor have I been able to come across any
> literature describing way of doing so.
You can find literature explaining why it's not possible. Key phrase: 'virial theorem'.
Paul
Earl
news:106270533...@iris.uk.clara.net:
Since the ICBM is the counterpart to the bullet your
interpretation is in error.
Consider a SLBM. The system consists of the shore facilities,
the sub (about $billion) and the 16 (now 25) birds (about $10
million each) -- expected kills per bird would be in the
100,000 range for each. So costs are in the $10,000 per kill.
A rifle can go for $100 range to the $5,000 range for a Barrent
50 cal. Bullets are in the 10 cent to $10 range.
The problem is costs are considered for the results not for the
entire system.
Comparable mistaken comparison would be calculating the cost to
get to orbit. Measured on a energy basis it is only $0.30 per
pound, Calculated on the costs of running NASA and you have to
start adding zeros all over the place.
Luke
> At atmospheric pressure, you'd
> need a cubic meter of plasma to contain a kilojoule of energy.
Err, make that 100 kilojoules of energy. Had a finger-brain disjunction there.
Luke
Brian Trosko
> interpretation is in error.
> Consider a SLBM. The system consists of the shore facilities,
> the sub (about $billion) and the 16 (now 25) birds (about $10
> million each) -- expected kills per bird would be in the
> 100,000 range for each. So costs are in the $10,000 per kill.
Um.
Those "birds" are MIRVed. A single Trident D-5 missile can carry 8 W88
warheads, so that's 800,000 range for each.
'course, they're about 30 million each, too, and 24 to the Ohio, not 25.
So still pretty close to 10k.
Spider Jerusalem
> The amount of energy released by a primordial black hole evaporating is
> much less than the energy released by the Sun every second, so this
> statement is clearly untrue.
>
Trolls. Tell lies.
So, yeah, it's clearly untrue....Kolkertroll cares not for such niceties as
Truth...
Jeroen
> Woudn't this depend on how many people you can pack into a
city? How do
> you reconcile nuking one lone dude in the middle of the
desert with just
> sniping him?
>
Depends on
a) Whether or not one has a nuke available.
b) How good a shot one is.
c) If he's armed. With anything.
--
"Man will become better when you show him what he is
like." - Chekhov
Erik Max Francis
> Trolls. Tell lies.
I don't think he's a troll. I just think he's someone who's too
interested in posting as often as possible and sounding smart that he
doesn't let little things like context and accuracy get in his way.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ It is impossible to love and be wise.
\__/ Francis Bacon
Ray Drouillard
"Luke" <lwc...@landau.chem.rochester.edu> wrote in message
news:428ca8b3.03090...@posting.google.com...
Doesn't your calculation depend on plasma acting like an ideal gas?
Some gases don't act like ideal gasses (steam, for instance). I
wouldn't expect plasma to do so.
OTOH, you would probably be within an order of magnitude or so ;-)
Ray
Luke
> "Luke" <lwc...@landau.chem.rochester.edu> wrote in message
> news:428ca8b3.03090...@posting.google.com...
> > lwc...@landau.chem.rochester.edu (Luke) wrote in message
> news:<428ca8b3.0309...@posting.google.com>...
> > > At atmospheric pressure, you'd
> > > need a cubic meter of plasma to contain a kilojoule of energy.
>
> Some gases don't act like ideal gasses (steam, for instance). I
> wouldn't expect plasma to do so.
The assumption is that the average energy per particle is much greater
than any binding energies that would couple the particles together, or
other "internal" energy parameters (such as an exchange correlation
energy). So it should work for hydrogen plasma at a temperature of
100 eV, but probably will have significant deviations at a temperature
of 15 eV (where the important energy here is the binding between the
electron and proton at 13.6 eV, except at extreme densities where the
exchange correlation energy will become larger still). Note that this
is entirely equivalent to the usual assumptions made for an ideal gas
of no intermolecular forces and no finite volume effects.
This result can be generalized to arbitrary internal forces, see
http://www.tn.utwente.nl/cdr/PolymeerDictaat/node42.html for example.
> OTOH, you would probably be within an order of magnitude or so ;-)
Heck, I'd expect it to be correct within a factor of two, except at
critical points (such as the recombination of the electrons with the
ions) or until you start getting close to solid densities.
Luke
pervect
> Indeed. I meant coherent as in phase-locked, not condensed.
> Atom-lasers. Bose-Einstein beams.
There's really no advantage to cooling your bullets to nanokelvin
temperatures. They work just as well at room temperature.
Mark Fergerson
> Stephan Aspridis wrote:
>
>> Paul Ciszek wrote:
>>
>>> As far as Coherent matter beams go, the military has had some success
>>> with weapons that use Fermi exclusion forces to accelerate a "pulse" of
>>> Quantum-entangled baryons and leptons.
Wait; that describes everything from nuclear bombs to
black-powder cannon!
>> You are evil and you know it ;-))))
>
>
> Indeed. I meant coherent as in phase-locked, not condensed.
> Atom-lasers. Bose-Einstein beams.
Um, you were thinking of "atom lasers" as weapons?
Alistair Reynolds' _Revelation Space_ mentions "boser"
weapons that sound like that; I s'pose if it meant "boson
amplification by stimulated emission of radiation" it should
be "baser" but that sounds weird.
Mark L. Fergerson
Earl
news:3F5B057D...@cox.net:
> Christian Thalmann wrote:
>> Stephan Aspridis wrote:
>>
>>> Paul Ciszek wrote:
>>>
>>>> As far as Coherent matter beams go, the military has had
>>>> some success with weapons that use Fermi exclusion forces
>>>> to accelerate a "pulse" of Quantum-entangled baryons and
>>>> leptons.
>
> Wait; that describes everything from nuclear bombs to
> black-powder cannon!
I think it can be stretched to include bows and arrows also.
John
"Luke" <lwc...@landau.chem.rochester.edu> wrote in message
news:428ca8b3.03090...@posting.google.com...
I believe you would need about 40 watts for a nice plasma rifle to work.
In the 40 watt range, at least.
Erik Max Francis
> I believe you would need about 40 watts for a nice plasma rifle to
> work.
> In the 40 watt range, at least.
If the 100 kJ figure is right, 40 W means you have to wait 40 minutes
per shot. Where are you getting this 40 W figure from?
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ There's this perfect girl / Living inside the shell
\__/ Lamya
Thomas Womack
>
>> I believe you would need about 40 watts for a nice plasma rifle to
>> work.
>> In the 40 watt range, at least.
>
>If the 100 kJ figure is right, 40 W means you have to wait 40 minutes
>per shot. Where are you getting this 40 W figure from?
The original _Terminator_ movie ("a pulsed plasma rifle in the
forty-watt range" is about 20% of Arnie's dialogue ...)
Tom
Brian Trosko
"Phased."
MikeyD
> > forty-watt range" is about 20% of Arnie's dialogue ...)
>
> "Phased."
Phased plasma??
I'll check it on Friday when they show it, but how can you have phased
plasma?
pervect
"Erik Max Francis" <m...@alcyone.com> wrote in message
news:3F5C2A80...@alcyone.com...
> John wrote:
>
> > I believe you would need about 40 watts for a nice plasma rifle to
> > work.
> > In the 40 watt range, at least.
>
> If the 100 kJ figure is right, 40 W means you have to wait 40 minutes
> per shot. Where are you getting this 40 W figure from?
From the California guvinotorial candidate, Arnold Schwarzeneger, of course.
Starring in "Terminator".
BTW - I hope he looses. Besides politics, I *really* want to hear him say
"I'll be back".
George W. Harris
wrote:
:> > The original _Terminator_ movie ("a pulsed plasma rifle in the
:
"I didn't *build* the fucking thing!"
--
e^(i*pi)+1=0
George W. Harris For actual email address, replace each 'u' with an 'i'.
Stephan Aspridis
>
> Phased plasma??
> I'll check it on Friday when they show it, but how can you have phased
> plasma?
>
>
Look here ;-) :
http://www.b5tech.com/misctech/weapons/handheldweapons/ppgpistol.html
regards,
Stephan
Erik Max Francis
> Phased plasma??
> I'll check it on Friday when they show it, but how can you have
> phased
> plasma?
Um ... it's _Terminator_?
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Silence is the most perfect expression of scorn.
\__/ George Bernard Shaw
John
And that's exactly why we don't *have* a phased plasma rifle available yet.
Ray Drouillard
It's the old particle/wave duality. In recent experiments, scientists
have gotten atoms to interfere with each other like light waves.
Ray Drouillard
Erik Max Francis
> It's the old particle/wave duality. In recent experiments, scientists
> have gotten atoms to interfere with each other like light waves.
That only makes sense at very low temperature. If you're talking about
plasma that's coming out of a weapon, it's hardly likely to be amenable
to Bose-Einstein condensation.
It's simply technobabble, so trying to extract meaning from it is a
waste of time.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ I can paint a portrait of myself / I will call me a black Mona Lisa
\__/ Lamya
Christian Thalmann
> Look here ;-) :
>
> http://www.b5tech.com/misctech/weapons/handheldweapons/ppgpistol.html
It says "triterium" for tritium. ;-P
Also, if I'm not mistaken, we have 100 W light bulbs in our
house... that's 2.5 times as powerful as such a plasma gun...
;-)
-- Christian Thalmann
cinga (at) gmx (dot) net
http://catharsis.netpeople.ch/
Christian Thalmann
for.
> Roughly, beam diameter = distance * wavelength / aperture diameter,
> with some constants of order unity depending on the initial intensity
> distribution across the aperture.
How stable are the components in a laser resonator? I mean,
by which factor must the beam cross-section in the resonator be
larger than on the target to avoid blowing up your mirrors?
Assume some highly efficient laser mechanism (free electron
laser, excimer etc) and adaptive mirrors/optical grids for
focusing.
Seeing how laser weapons would need a wide barrel, wouldn't they
be much more vulnerable on the battlefield than regular guns?
> Continuous lasers might work better against people if employed as long
> range flame throwers - give third degree burns to exposed skin, second
> degree burns under light clothing, and ignite cloth for only about a
> megajoule per square meter. Burns over your target's front torso,
> arms, and face, plus burning hair and clothing, will likely be
> immediately incapacitating (especially since he is now blind) and
> ultimately lethal.
Ouch. These would have a very bad reputation among human rights
activists, I'm sure. They'd probably be banned by many societies
too.
> A single nanosecond pulse will cause a surface explosion. Pack on the
> order of 10 to 100 kilojoules into the pulse for a blast big enough to
> cause lethal internal trauma, disable limbs, and the like.
About the yield of a hand grenade... that would certainly work
well even through armor, right?
How would you guesstimate the maximum power density in the
resonator, ie would a 100 kJ pulse be feasible in short enough a
time with a pistol- or maybe rocket launcher-sized weapon?
> I can't think of any way to keep a plasma at significantly greater
> than atmospheric pressure from exploding as soon as it is no longer
> confined by your weapon, nor have I been able to come across any
> literature describing way of doing so.
Well, the GURPS armory seems to suggest making a low-density
tunnel through the atmosphere with a laser... don't know how
realistic that is.
http://www.gurpsmaster.de/2300weap.htm#plasmaguns
> Incidently, a hit anywhere on the body by a particle beam potent
> enough to cause physical damage will pretty much ensure you've just
> taken a lethal dose of radiation. You might survive the immediate
> injury from hole it puts through you, so you'll have time to write
> your will and say goodbye to your loved ones. That is, unless you
> take enough radiation that your brain cells start dying, in which case
> you've got a few minutes of consciousness left.
Ouch... I guess that sort of weapon would only be sensible for
unmanned remote-controlled or autonomous weapon systems.
> In atmosphere, electron beams seem to be self-focusing, so you can get
> around the mutual repulsion of the electrons. My guess is that they
> are still deflected by the earth's magnetic field, though.
Sounds like a small effect. Though it would make magnetic
shielding viable.
Another question: Laser-ionized paths to transmit an electric
current seems to work for taser-sized jolt. Could such a
technology also be applied to much more dangerous amperages?
Or would those only cause surface effects? Either way, one
would probably be better off using the lasers themselves as
weapons.
MikeyD
> > I'll check it on Friday when they show it, but how can you have phased
> > plasma?
> >
> >
> Look here ;-) :
>
> http://www.b5tech.com/misctech/weapons/handheldweapons/ppgpistol.html
>
as a meaningless concept.
Erik Max Francis
> Well, nice, but I still don't see how they phased the plasma. It
> strikes me
> as a meaningless concept.
It's technobabble, why would you expect it to have meaning?
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ The perfection of innocence, indeed, is madness.
\__/ Arthur Miller
Luke
> Luke, thanks for the write-up, that's exactly what I was looking
> for.
>
>
> > Roughly, beam diameter = distance * wavelength / aperture diameter,
> > with some constants of order unity depending on the initial intensity
> > distribution across the aperture.
>
> How stable are the components in a laser resonator? I mean,
> by which factor must the beam cross-section in the resonator be
> larger than on the target to avoid blowing up your mirrors?
> Assume some highly efficient laser mechanism (free electron
> laser, excimer etc) and adaptive mirrors/optical grids for
> focusing.
I don't work directly with lasers as part of my job (I'm a theorist)
but I do work with people who use lasers as part of their everyday
work (the experimenters). From what I've seen in the labs, and from
what I can recall, the Ti:sapphire lasers with pulses of roughly 100
femptosecond duration, 1 millijoule energy, and about 1 kilohertz
repitition rate have apertures of about a centimeter wide. This means
they can take a peak power of at least 10 Gigawatts per square
centimeter and a time averaged power of at least 1 Joule per square
centimeter. I suspect that the time averaged power is a vast
underestimate, and repitition rate is limited by other factors. Going
from memory, military experimental deuterium fluoride laser (named
MIRACL) put out a classified amount of power described in the
"Megawatt range" through a window about 10 cm by 30 cm. This means
that the optics could handle a time averaged power of 3 kilowatts to
30 kilowatts per square centimeter.
> Seeing how laser weapons would need a wide barrel, wouldn't they
> be much more vulnerable on the battlefield than regular guns?
I suspect they would be more fragile than normal guns, because the
alignment of the internal optics is more delicate, the laser crystals
could crack (for solid state lasers), the electronics could fail, and
so on. Meanwhile, guns are made of tough and durable materials like
steel with a relatively simple construction.
The term "barrel" is something of a misnomer for lasers (although
people will undoubtedly use it). The part of the laser optics that
will likely need to be the largest is the "beam pointer" mirror - the
final mirror which the laser light reflects off of, used to steer the
beam onto its targets. This is the mirror which sets the limits to
which the beam can focus (although the gross focusing can largely be
done with smaller, internal mirrors). Half a meter to one meter beam
pointers will probably be typical for "artillery" type applications,
capable of striking many kilometers away. Presumably this mirror
would be made of something fairly tough (at least on the outside) and
have various safeguards to keep it clean (I can see it being kept
shuttered when not in use, and using a low positive pressure when in
use to make sure dust does not get into the mirror assembly). Still,
it would undoubtedly be more fragile than the steel barrels of
artillery pieces. On the other hand, a one meter mirror (maybe one
and a half meters wide with all the assemblies and fixtures included)
would not present more of a target than the usual frontal area of a
modern artillery piece or battle tank.
For laser smallarms, a 10 cm mirror would provide a range of several
hundred meters for typical values of wavelength and pulse energy that
I have calculated. This would be suitable for applications which are
met by rifles today (again, rifle would be a misnomer for lasers). Of
course, in this case it is the arms and hands of the infantryman doing
the steering of the final mirror - by moving the entire gun-shaped
laser assembly! Fine beam steering (for automatic beam stabilization,
for example) could still be done by internal optics and electronics,
giving the effect of the image stabilization routines used for today's
camcorders to correct for jitter. This, and the ability of a laser
beam to ignore gravity and wind conditions, would likely make laser
smallarms super-accurate compared to modern rifles. Again, the area
of a 10 cm mirror would not make the laser any more vulnerable than
most modern firearms, but the mirror itself would probably be more
fragile than a steel barrel, and could have problems if it got dirty.
> > Continuous lasers might work better against people if employed as long
> > range flame throwers - give third degree burns to exposed skin, second
> > degree burns under light clothing, and ignite cloth for only about a
> > megajoule per square meter. Burns over your target's front torso,
> > arms, and face, plus burning hair and clothing, will likely be
> > immediately incapacitating (especially since he is now blind) and
> > ultimately lethal.
>
> Ouch. These would have a very bad reputation among human rights
> activists, I'm sure. They'd probably be banned by many societies
> too.
I wouldn't be suprized, although the effects are not any worse than
modern flamethrowers, other than their longer range. In terms of
energy usage, however, this is the least efficient way of killing
people with a laser. If available, pulsed laser weapons will likely
be prefered.
> > A single nanosecond pulse will cause a surface explosion. Pack on the
> > order of 10 to 100 kilojoules into the pulse for a blast big enough to
> > cause lethal internal trauma, disable limbs, and the like.
>
> About the yield of a hand grenade... that would certainly work
> well even through armor, right?
A 100 kilojoule pulse incident on a human torso would have about the
same effect as duct taping 20 grams of TNT to your target's chest and
then detonating it. This would undoubtedly crush much of the chest
and send rib fragments flying through lungs, heart, blood vessels, and
airways. Incident on rigid armor, the shattered peices of the armor
now become fast moving projectiles to perforate your target. If the
armor is thick enough to resist shattering, the shock wave can still
spall a layer off the back of the armor to act as fragments. The
shock wave itself might well be enough to cause ruptured bowels and
hemorrhaged lungs.
There are ways to make armor that resist this kind of damage, however.
Multiple layers of different density will cause multiple reflections
of the shock wave, weakening it as it passes each boundary. A layer
of kevlar under the rigid armor could stop spalled fragments.
10 kilojoule pulses would be about like the detonation of 2 grams of
TNT. Not having performed experiments of detonating various amounts
of high explosives against large mammals, I am not quite sure how
lethal this would be although it would certainly cause nasty injuries.
Hence this is about the lower range of my estimate for the minimum
energy for a single pulse that would reliably dispatch a human target.
> How would you guesstimate the maximum power density in the
> resonator, ie would a 100 kJ pulse be feasible in short enough a
> time with a pistol- or maybe rocket launcher-sized weapon?
With modern technology and forseable advances, no. We have lasers
that produce 100 kilojoule, nanosecond pulses, but they take up the
major part of a large building and take hours to cool down between
shots. This is why I lean towards lasers that produce a train of
thousands of pulses of about 1 Joule each, delivered in a millisecond
timescale. This might be feasable in the future in a laser that could
be conveniently carried, although today's lasers are not up to the
task. Still, unforseen advances could make 100 kilojoule pulse lasers
in a portable package possible.
> > I can't think of any way to keep a plasma at significantly greater
> > than atmospheric pressure from exploding as soon as it is no longer
> > confined by your weapon, nor have I been able to come across any
> > literature describing way of doing so.
>
> Well, the GURPS armory seems to suggest making a low-density
> tunnel through the atmosphere with a laser... don't know how
> realistic that is.
Well, you probably could do this, bit it wouldn't get you anywhere.
If the plasma is at greater than atmospheric pressure, it will still
expand against the sides of the evacuated tunnel - remember, the
"walls" of the tunnel are pushing in with the pressure of the
atmosphere, the plasma is pushing out with however much pressure it
has. If the plasma has greater pressure, it will explode the tunnel.
There are ways to magnetically confine plasmas, but these rely on
electrical currents that run axially or circumferentially to the
plasma stream. I cannot think of any way to get even transient
currents through the atmosphere at long distances to confine the
plasma.
> > Incidently, a hit anywhere on the body by a particle beam potent
> > enough to cause physical damage will pretty much ensure you've just
> > taken a lethal dose of radiation. You might survive the immediate
> > injury from hole it puts through you, so you'll have time to write
> > your will and say goodbye to your loved ones. That is, unless you
> > take enough radiation that your brain cells start dying, in which case
> > you've got a few minutes of consciousness left.
>
> Ouch... I guess that sort of weapon would only be sensible for
> unmanned remote-controlled or autonomous weapon systems.
Yes, or armored fighting vehicles with heavy frontal armor - the armor
protects the crew when the beam is on. Incidently, this is the beam
weapon that seems like it would have the most attempts to outlaw it.
> Another question: Laser-ionized paths to transmit an electric
> current seems to work for taser-sized jolt. Could such a
> technology also be applied to much more dangerous amperages?
> Or would those only cause surface effects?
They could indeed handle much more dangerous amperages. Modern
research into the atmospheric propagation of laser pulses about 100
femptoseconds long show that if concentrated to a sharp focus, they
form narrow self-focusing beams that ionize the air they pass through
and that propagate for hundreds of meters. These beams have been used
to guide intense electrical discharges with voltages just below that
necessary to cause atmospheric breakdown around the electrodes. They
are promising candidates for guiding lightning strokes away from
sensative equipment. A parallel pair of these laser ionized channels
could form a waveguide down which high voltage AC current could be
passed. This could be used to electrocute human targets, or just
shock them into immobility. Higher frequency currents could burn out
electrical circuits of the target, similar to an EMP.
> Either way, one
> would probably be better off using the lasers themselves as
> weapons.
If you want to blast or kill armored targets, yes. The ability of
guided electric currents to incapacitate while not causing permanent
injury, or to disable electronics while not damaging structures of
living organisms could be quite useful for law enforcement.
Luke
Warren Okuma
"Erik Max Francis" <m...@alcyone.com> wrote in message
news:3F5F85B1...@alcyone.com...
> MikeyD wrote:
>
> > Well, nice, but I still don't see how they phased the plasma. It
> > strikes me
> > as a meaningless concept.
>
> It's technobabble, why would you expect it to have meaning?
>
picked it up and thought it might either confuse the humans, annoy the
scientifically savvy, and/or intimidate others. I don't think that the
Terminators care.
Christian Thalmann
> Going
> from memory, military experimental deuterium fluoride laser (named
> MIRACL) put out a classified amount of power described in the
> "Megawatt range" through a window about 10 cm by 30 cm. This means
> that the optics could handle a time averaged power of 3 kilowatts to
> 30 kilowatts per square centimeter.
If the resonator of a laser can withstand that, wouldn't an
enemy's armor do the same? Especially if we're talking a rifle-
sized pulse-train laser... or would the laser be focused down
into significantly higher power density at the target? If the
material can handle Megawatts, wouldn't that be the ballpark of
your Kilojoule-in-a-millisecond pulse trains?
> Presumably this mirror
> would be made of something fairly tough (at least on the outside) and
> have various safeguards to keep it clean (I can see it being kept
> shuttered when not in use, and using a low positive pressure when in
> use to make sure dust does not get into the mirror assembly).
Could high-frequency vibration of the emitter mirror keep it
clean? Maybe the shutter would be closed by default, opening
only at the pressure point of the trigger...
> For laser smallarms, a 10 cm mirror would provide a range of several
> hundred meters for typical values of wavelength and pulse energy that
> I have calculated. This would be suitable for applications which are
> met by rifles today (again, rifle would be a misnomer for lasers). Of
> course, in this case it is the arms and hands of the infantryman doing
> the steering of the final mirror - by moving the entire gun-shaped
> laser assembly!
That's assuming a gun-shaped laser... but a combat laser might
as well have its resonator vertically across the back of the
soldier, with a rotating emitter mirror above his shoulder, which
he could aim with his eye-tracking goggles. =P
> I wouldn't be suprized, although the effects are not any worse than
> modern flamethrowers, other than their longer range. In terms of
> energy usage, however, this is the least efficient way of killing
> people with a laser. If available, pulsed laser weapons will likely
> be prefered.
So aren't flamethrowers stigmatized in any way?
> 10 kilojoule pulses would be about like the detonation of 2 grams of
> TNT. Not having performed experiments of detonating various amounts
> of high explosives against large mammals, I am not quite sure how
> lethal this would be although it would certainly cause nasty injuries.
> Hence this is about the lower range of my estimate for the minimum
> energy for a single pulse that would reliably dispatch a human target.
I guess unless you want to spend your whole magazine for a handful
of 100 kJ grenade shots, it would be better to invest 10 kJ into
a pulse train on steroids... that's assuming the pulse-train idea
is scalable in energy. That oughta have significantly more impact
that a rifle bullet.
> There are ways to magnetically confine plasmas, but these rely on
> electrical currents that run axially or circumferentially to the
> plasma stream. I cannot think of any way to get even transient
> currents through the atmosphere at long distances to confine the
> plasma.
Couldn't currents in the plasma create a magnetic bottle for
itself?
Ball lightning appears to exist, so there does seem to be a method
for keeping plasma together. Though I don't know about the
pressure, it might well be around 1 bar for ball lightning, which
would make it too weak for weaponry.
>>Ouch... I guess that sort of weapon would only be sensible for
>>unmanned remote-controlled or autonomous weapon systems.
>
>
> Yes, or armored fighting vehicles with heavy frontal armor - the armor
> protects the crew when the beam is on. Incidently, this is the beam
> weapon that seems like it would have the most attempts to outlaw it.
Yeah. Reminds me of the Cold Light in the Mark Brandis books I
read when I was really young. =P
> A parallel pair of these laser ionized channels
> could form a waveguide down which high voltage AC current could be
> passed. This could be used to electrocute human targets, or just
> shock them into immobility. Higher frequency currents could burn out
> electrical circuits of the target, similar to an EMP.
But such effects would be relatively easy to block with conductive
armor, right? Or would the high amperage fuse the conductive
layer? Would a high-temperature superconductor work?
Luke
> Luke wrote:
> > Christian Thalmann <cingaDo...@gmx.net> wrote in message news:<3F5F2BD6...@gmx.net>...
>
> > Going
> > from memory, military experimental deuterium fluoride laser (named
> > MIRACL) put out a classified amount of power described in the
> > "Megawatt range" through a window about 10 cm by 30 cm. This means
> > that the optics could handle a time averaged power of 3 kilowatts to
> > 30 kilowatts per square centimeter.
>
> If the resonator of a laser can withstand that, wouldn't an
> enemy's armor do the same? Especially if we're talking a rifle-
> sized pulse-train laser... or would the laser be focused down
> into significantly higher power density at the target? If the
> material can handle Megawatts, wouldn't that be the ballpark of
> your Kilojoule-in-a-millisecond pulse trains?
The laser would be focused down to a tiny spot size at the target. A
laser emitting a 1 micron near IR beam with a 10 cm aperture could
focus its beam down to a 1 mm spot at 100 meters. That would make it
10,000 times more intense. For ultrashort pulses (as demonstrated
with millijoule energies on the order of 100 femptoseconds) the
non-linear self focusing can take over at tight focus and squeeze the
beem down even narrower. (The self focusing regime is lossy, however,
so you would probably want to focus to a self focusing beam right in
front of your target.)
> > Presumably this mirror
> > would be made of something fairly tough (at least on the outside) and
> > have various safeguards to keep it clean (I can see it being kept
> > shuttered when not in use, and using a low positive pressure when in
> > use to make sure dust does not get into the mirror assembly).
>
> Could high-frequency vibration of the emitter mirror keep it
> clean?
I don't know. I've never heard of anything like this working before,
but maybe it is for lack of trying.
> Maybe the shutter would be closed by default, opening
> only at the pressure point of the trigger...
Yeah, like a camera.
> > For laser smallarms, a 10 cm mirror would provide a range of several
> > hundred meters for typical values of wavelength and pulse energy that
> > I have calculated. This would be suitable for applications which are
> > met by rifles today (again, rifle would be a misnomer for lasers). Of
> > course, in this case it is the arms and hands of the infantryman doing
> > the steering of the final mirror - by moving the entire gun-shaped
> > laser assembly!
>
> That's assuming a gun-shaped laser... but a combat laser might
> as well have its resonator vertically across the back of the
> soldier, with a rotating emitter mirror above his shoulder, which
> he could aim with his eye-tracking goggles. =P
Might work, but you'd have to be careful he doesn't shoot his own neck
off when he is looking at something over the other shoulder. Maybe a
pair of mirrors, one over each shoulder, might work better. Perhaps
if the laser was on the lower back or thigh, with the beam pointer at
the hips, it would restrict mobility less. Maybe the best solution is
to carry the laser, but still have the beam be aimed by a rotating
beam pointer that tracks the eyes. Who knows?
> > I wouldn't be suprized, although the effects are not any worse than
> > modern flamethrowers, other than their longer range. In terms of
> > energy usage, however, this is the least efficient way of killing
> > people with a laser. If available, pulsed laser weapons will likely
> > be prefered.
>
> So aren't flamethrowers stigmatized in any way?
Only by their ineffectiveness. They are short ranged, have virtually
no penetration, and limited ammunition.
> > There are ways to magnetically confine plasmas, but these rely on
> > electrical currents that run axially or circumferentially to the
> > plasma stream. I cannot think of any way to get even transient
> > currents through the atmosphere at long distances to confine the
> > plasma.
>
> Couldn't currents in the plasma create a magnetic bottle for
> itself?
If you have circumferential currents, the plasma will squirt out the
ends. You can't have axial currents, because there needs to be a
return path. A more complicated arrangement might work, but ...
> Ball lightning appears to exist, so there does seem to be a method
> for keeping plasma together. Though I don't know about the
> pressure, it might well be around 1 bar for ball lightning, which
> would make it too weak for weaponry.
There are general theorems relating the pressure in a plasma
containing currents and magnetic fields to the extreior pressure when
the plasma is in a stable configuration. Basically, ball lightning,
if it is a plasma, would need to be at around atmospheric pressure.
> >>Ouch... I guess that sort of weapon would only be sensible for
> >>unmanned remote-controlled or autonomous weapon systems.
> >
> >
> > Yes, or armored fighting vehicles with heavy frontal armor - the armor
> > protects the crew when the beam is on. Incidently, this is the beam
> > weapon that seems like it would have the most attempts to outlaw it.
>
> Yeah. Reminds me of the Cold Light in the Mark Brandis books I
> read when I was really young. =P
I have not read these, I'm afraid. What was cold light?
> > A parallel pair of these laser ionized channels
> > could form a waveguide down which high voltage AC current could be
> > passed. This could be used to electrocute human targets, or just
> > shock them into immobility. Higher frequency currents could burn out
> > electrical circuits of the target, similar to an EMP.
>
> But such effects would be relatively easy to block with conductive
> armor, right? Or would the high amperage fuse the conductive
> layer? Would a high-temperature superconductor work?
A sheet of aluminum foil would probably be all that is necessary to
block electrocution effects, although capacitative coupling might
still affect you if the conductive layer is close to your skin if you
are not fully surrounded by it. The EMP effects are supposed to be
able to get through "cracks" in the conductive shell of automobiles,
but this might just be hype from the company that has the patent on
this method. Enough current would melt or vaporize a conductive
layer, of course, causing third degree burns when it arced through to
the skin. A room temperaure superconductor would be as good as a
conductor, assuming the current did not exceed the critical current of
the superconductor and assuming the frequency of the current is not
too high.
Luke
Christian Thalmann
> The laser would be focused down to a tiny spot size at the target. A
> laser emitting a 1 micron near IR beam with a 10 cm aperture could
> focus its beam down to a 1 mm spot at 100 meters. That would make it
> 10,000 times more intense. For ultrashort pulses (as demonstrated
> with millijoule energies on the order of 100 femptoseconds) the
> non-linear self focusing can take over at tight focus and squeeze the
> beem down even narrower. (The self focusing regime is lossy, however,
> so you would probably want to focus to a self focusing beam right in
> front of your target.)
Pretty cool. Though I wonder if the pulse-train method would
still work, since it would have to be able to hit the same spot
over and over again during a millisecond. That would require a
very steady hand (or some very steady adaptive optics) to attain
over 100 meters.
How does the spot size scale up when I increase distance for a
constant aperture?
>>Maybe the shutter would be closed by default, opening
>>only at the pressure point of the trigger...
>
>
> Yeah, like a camera.
Add 10 cm or so of hollow tube in front of the emitter and
maybe a fan to create an air flow away from the emitter. That
oughta keep it from the worst dirt.
I wonder how safe it would be in rain, though, or in splashy
sea conditions. Would the refractions from water droplets be
dangerous? Or would the laser just vaporize its way through?
>>That's assuming a gun-shaped laser... but a combat laser might
>>as well have its resonator vertically across the back of the
>>soldier, with a rotating emitter mirror above his shoulder, which
>>he could aim with his eye-tracking goggles. =P
>
>
> Might work, but you'd have to be careful he doesn't shoot his own neck
> off when he is looking at something over the other shoulder. Maybe a
> pair of mirrors, one over each shoulder, might work better. Perhaps
> if the laser was on the lower back or thigh, with the beam pointer at
> the hips, it would restrict mobility less. Maybe the best solution is
> to carry the laser, but still have the beam be aimed by a rotating
> beam pointer that tracks the eyes. Who knows?
The adaptive-optics emitter would most likely be a mirror rather
than a lens, right? In that case, the design would call for a
resonator perpendicular to the beam direction, with the emitter
mirror tilted 45°... or then two such mirrors that fold the beam
back into an axis parallel to the resonator.
What about diffraction grids? Could they be used as sturdy
adaptive optics? Would that allow the beam to pass straight on
through the grid and out? Then the classical rifle design would
work well.
>>Couldn't currents in the plasma create a magnetic bottle for
>>itself?
>
>
> If you have circumferential currents, the plasma will squirt out the
> ends. You can't have axial currents, because there needs to be a
> return path. A more complicated arrangement might work, but ...
You can have axial currents in a smoke ring... would that help?
In fact, you *need* axial currents on the surface for a smoke
ring to propagate through a medium. Superimpose circumferential
currents on that, and you have yourself a flying stellarator.
=) (Admittedly, I don't know what stellarator fields are
supposed to look like...)
>>Yeah. Reminds me of the Cold Light in the Mark Brandis books I
>>read when I was really young. =P
>
>
> I have not read these, I'm afraid. What was cold light?
You haven't missed much... cold light was a banned radiation
weapon that caused a radioactive mess wherever it hit. It
sounds pretty much like what you said about electron beams.
BTW, your data would fit perfectly into that sci-fi science FAQ
I've seen on this list a few days ago... countless interested
sci-fi writers and/or fans probably ask themselves about the
physics of energy weapons all the time...
-- Christian Thalmann
JWMeritt
>I'm sure I read that a nuclear ICBM is much cheaper per-kill than, say, a
>rifle.
I hope that you don't think the reason for an ICBM is to kill a person.
I personally find it interesting that a rifle is one of the very few products
that, when used as directed, is INTENDED to kill people. On the other hand, if
you use an ICBM you have already lost. As Whopper said - "An interesting game.
The only way to win is not to play."
..........................................................................
..........................................
http://profiles.yahoo.com/jwmeritt and http://hometown.aol.com/jwmeritt/
James W. Meritt, CISSP, CISA
Luke
> Luke wrote:
>
> > The laser would be focused down to a tiny spot size at the target. A
> > laser emitting a 1 micron near IR beam with a 10 cm aperture could
> > focus its beam down to a 1 mm spot at 100 meters. That would make it
> > 10,000 times more intense. For ultrashort pulses (as demonstrated
> > with millijoule energies on the order of 100 femptoseconds) the
> > non-linear self focusing can take over at tight focus and squeeze the
> > beem down even narrower. (The self focusing regime is lossy, however,
> > so you would probably want to focus to a self focusing beam right in
> > front of your target.)
>
> Pretty cool. Though I wonder if the pulse-train method would
> still work, since it would have to be able to hit the same spot
> over and over again during a millisecond. That would require a
> very steady hand (or some very steady adaptive optics) to attain
> over 100 meters.
I was thinking you would use electronically guided optics for active
tracking of the target over that millisecond. To first order, you
only need to track the instantaneous angular velocity of the target's
image as estimated from (for example) the previous 1/10 of a second.
Consider if you are swinging your laser at 1 radian per second. This
corresponds to an angular spread in the pulse train of 1 milliradian
in the one millisecond it takes to emit. At 100 meters, this
corresponds to a total spread of 10 cm. The temporary cavities
caused by the passage of a high velocity rifle bullet are about this
large, so it may be that no active tracking during the emission of the
pulse train is needed for many cases. However, with optical beam
stabilization already in place, you have pretty much all the
components needed to guess the target's angular velocity and
compensate by slewing the adaptive optics mirrors at the same angular
velocity to compensate.
Interestingly, this reliance on active optics to aim, focus, and track
with the beam might mean that reflective armor will be useful after
all. A highly reflective surface offers no protection against a high
intensity short pulsed beam - the leading edge of the beam flashes a
thin layer of the surface to plasma, and this plasma absorbs the rest
of the beam so the optical properties of the surface do not matter.
However, if the surface is highly reflective, the electronics that
estimate the target's distance and angular velocity could be fooled by
the reflections, resulting in a beam with little penetration.
> How does the spot size scale up when I increase distance for a
> constant aperture?
The spot radius scales linearly with distance (see my first post in
this thread). This means the intensity falls off as one over the
square of the distance.
> >>Maybe the shutter would be closed by default, opening
> >>only at the pressure point of the trigger...
> >
> >
> > Yeah, like a camera.
>
> Add 10 cm or so of hollow tube in front of the emitter and
> maybe a fan to create an air flow away from the emitter. That
> oughta keep it from the worst dirt.
Yup. That's the positive pressure idea I was talking about earlier.
Another idea is to use a plasma window. These were developed for
particle beams. While the beam is in the accelerator, you want to
keep it in a high vacuum. But sometimes you want to do experiments
where the beam exits the apparatus and goes into the atmosphere.
Modern particle beams tend to have the thermal properties of a
blowtorch (if not even more intense), so most material windows would
not last long (and this is not even mentioning the radiation damage).
One idea was to create a low density helium plasma and shoot it across
the window opening at high velocities. Collect the helium on the
other side. This turns out to provide a window that can withstand an
atmosphere of pressure on one side and vacuum on the other with very
little leakage. For a laser, where you do not need vacuum for beam
propagation, such a plasma window might be adequate to keep out dust,
mist, rain, twigs, gnats, and the occasional curious hamster when the
shutter is open.
> I wonder how safe it would be in rain, though, or in splashy
> sea conditions. Would the refractions from water droplets be
> dangerous? Or would the laser just vaporize its way through?
With light that has a wavelength from a little longer than 1 micron to
about 0.3 or 0.2 microns (and this spans the entire visible range),
there is a very real danger of beam blindness from multiple
reflections of the beam. Even a tiny fraction of the original beam
intensity, if reflected into the eye, will be focused onto the retina
with sufficient intensity to cause burning and scarring. This will
permanently damage your eyesight, although it may not be obvious
(people do not notice small regions missing from their field of vision
since the brain "fills in" with information from surrounding areas, as
is evident from the blind spot on all of our retinas where the optic
nerve attaches). More intense reflections can cause burning over a
wider area, and even complete loss of eyesight in the affected eye.
One solution would be to use light of significantly longer wavelength
than about 1 micron, since the materials of the eye are opaque to
these wavelengths. I believe, for example, that 1.5 micron light is
eye safe. Unfortunately, the longer the wavelength, the less tightly
you can focus your laser at any given distance. Using light with a
wavelength shorter than that which is passed by the eye probably will
not work, since this will be absorbed by the atmosphere as well. If
you do use light that can damage eyesight, wear protective goggles
when using your laser.
Rain and mist, of course, as well as smoke, fog, smog, and other
suspended particles in the atmosphere will serve to scatter light from
the beam, attenuating it with distance so that it will cause less
damage at long ranges. For visible light lasers, one rule is that if
you can see it, your beam will reach it. If you can see it clearly,
your beam will reach it with nearly full intensity. Longer
wavelengths tend to get through aerosols with a small particle size
better than shorter wavelengths, so using eye-safe 1.5 micron IR or
longer wavelengths might be an advantage in bad seeing conditions.
This is not true, however, when the particle size gets to be about the
same size or larger than the wavelength of the light you are using.
In addition, when laser beams enter the self focusing regime, I recall
hearing that they are able to get through clouds much better than
non-self focusing beams. In conditions of poor seeing, it might be
best to focus your beam to a self focusing beam before you start to
get significant attenuation. The self focusing beam looses energy
continuously due to the formation of plasma as it propagates, but it
can propagate for hundreds of meters. When the plasma losses are
smaller than the losses due to beam scattering, this may end up being
the preferred route.
> The adaptive-optics emitter would most likely be a mirror rather
> than a lens, right? In that case, the design would call for a
> resonator perpendicular to the beam direction, with the emitter
> mirror tilted 45°... or then two such mirrors that fold the beam
> back into an axis parallel to the resonator.
I expect you would use many mirrors in the optical path. This way,
rather than making large deformations or movements of one mirror, you
could accomplish the active beam aiming, stabilization and focusing by
making small deformations on many mirrors. These small deformations
could be made by an array of piezoelectric motors mounted just behind
the surface of a flexible mirror. The mirrors themselves would
probably not be silvered or aluminized glass but rather a thin sheet
of ultra-high reflectivity optical bandgap materials on a flexible
backing.
> >>Couldn't currents in the plasma create a magnetic bottle for
> >>itself?
> >
> >
> > If you have circumferential currents, the plasma will squirt out the
> > ends. You can't have axial currents, because there needs to be a
> > return path. A more complicated arrangement might work, but ...
>
> You can have axial currents in a smoke ring... would that help?
> In fact, you *need* axial currents on the surface for a smoke
> ring to propagate through a medium. Superimpose circumferential
> currents on that, and you have yourself a flying stellarator.
> =) (Admittedly, I don't know what stellarator fields are
> supposed to look like...)
It sounds good, except that the mutual repulsion of the currents will
make the smoke ring tend to explode. Now you need the sum of the
thermal pressure plus the pressure from the interior currents to be
less than the atmospheric pressure.
> >>Yeah. Reminds me of the Cold Light in the Mark Brandis books I
> >>read when I was really young. =P
> >
> >
> > I have not read these, I'm afraid. What was cold light?
>
> You haven't missed much... cold light was a banned radiation
> weapon that caused a radioactive mess wherever it hit. It
> sounds pretty much like what you said about electron beams.
Ah. Got it. It is slightly better in this case, though, as electron,
x-ray, or gamma ray beams do not leave lingering radioactivity, just a
pulse of ionizing radiation scattered from the beam itself or from
excited core electron states in the atoms of the atmosphere or target
giving off x-rays as they decay (well, with high enough energy
electrons or gamma rays, the beam could excite higher nuclear energy
states, which would then result in gamma decay that could be long
lived). A neutron beam, on the other hand, would turn whatever it hit
radioactive through neutron capture.
> BTW, your data would fit perfectly into that sci-fi science FAQ
> I've seen on this list a few days ago... countless interested
> sci-fi writers and/or fans probably ask themselves about the
> physics of energy weapons all the time...
I'm not really sure what it takes to modify the FAQ for this list,
though. I've occasionally thought about writing up my thoughts on
beam weapons, because I seem to answer the same questions a lot.
However, often intelligent questions or comments in the resulting
discussions prompt me to think more about the subject, and so I learn
something, too.
Luke
John Park
>[...]
> with the beam might mean that reflective armor will be useful after
> all. A highly reflective surface offers no protection against a high
> intensity short pulsed beam - the leading edge of the beam flashes a
> thin layer of the surface to plasma, and this plasma absorbs the rest
> of the beam so the optical properties of the surface do not matter.
> rather than making large deformations or movements of one mirror, you
> could accomplish the active beam aiming, stabilization and focusing by
> making small deformations on many mirrors. These small deformations
> could be made by an array of piezoelectric motors mounted just behind
> the surface of a flexible mirror. The mirrors themselves would
> probably not be silvered or aluminized glass but rather a thin sheet
> of ultra-high reflectivity optical bandgap materials on a flexible
> backing.
>
--John Park
Christian Thalmann
>>The mirrors themselves would
>>probably not be silvered or aluminized glass but rather a thin sheet
>>of ultra-high reflectivity optical bandgap materials on a flexible
>>backing.
>>
>
> If this works for the laser optics, why wouldn't it work for armour?
Luke answered that a few posts ago. The laser intensity at the
target is several orders of magnitude greater than in the
resonator, because it's focused down to about a hundredth of the
radius of the resonator.
John Schilling
>Luke wrote:
>> Christian Thalmann <cingaDo...@gmx.net> wrote in message news:<3F5F2BD6...@gmx.net>...
> > Going
>> from memory, military experimental deuterium fluoride laser (named
>> MIRACL) put out a classified amount of power described in the
>> "Megawatt range" through a window about 10 cm by 30 cm. This means
>> that the optics could handle a time averaged power of 3 kilowatts to
>> 30 kilowatts per square centimeter.
>If the resonator of a laser can withstand that, wouldn't an
>enemy's armor do the same? Especially if we're talking a rifle-
>sized pulse-train laser... or would the laser be focused down
>into significantly higher power density at the target? If the
>material can handle Megawatts, wouldn't that be the ballpark of
>your Kilojoule-in-a-millisecond pulse trains?
A suit of armor with the thickness and composition of rifle-barrel
steel would be proof against ordinary rifle bullets; that doesn't
make the rifle a useless weapon. Same principle here.
The laser resonator has the edge over the armor for several reasons,
the most obvious being simple mass - the laser designer knows exactly
what parts of his system will get the full intensity of the beam, and
not only face those surfaces with his best mirrors but back them with
his beefiest heat sinks and active cooling systems. The armor designer
has to spread his defenses over the entire surface of the target.
On top of that, the laser mirrors are mostly internal components, and
so can be kept much cleaner than the target's mirror-armored surface.
They also don't face the design conflicts of the target surface, which
must not only be armored against lasers but against bullets, hailstones
and clumsy bumps and scratches by the user, and must be camoflaged in
the visible, IR, and microwave ranges of the spectrum.
And, yes, in most scenarios the laser will be focused to a spot smaller
than its own resonator mirrors.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *
Anton Sherwood
> I personally find it interesting that a rifle is one of the very few
Not true: guns are used far more often to influence someone's behavior
than to kill him. Perhaps you meant `when activated'.
--
Anton Sherwood, http://www.ogre.nu/
Christian Thalmann
> Consider if you are swinging your laser at 1 radian per second. This
> corresponds to an angular spread in the pulse train of 1 milliradian
> in the one millisecond it takes to emit. At 100 meters, this
> corresponds to a total spread of 10 cm.
Well, 1 radian per second is pretty freaking huge. At that range,
it would mean for the target to go at 100 m/s -- about twice as
fast as your average freeway speeding ticket earner. So for any
slower target, just keeping the laser stable is going to keep it
within a cm for any non-vehicular enemy. Against a vehicle,
you'd probably use the 100 kJ grenade-shots anyway.
> However, if the surface is highly reflective, the electronics that
> estimate the target's distance and angular velocity could be fooled by
> the reflections, resulting in a beam with little penetration.
A neat effect, except that you'll also gleam in the sun like a
christmas tree.
>>How does the spot size scale up when I increase distance for a
>>constant aperture?
>
>
> The spot radius scales linearly with distance (see my first post in
> this thread). This means the intensity falls off as one over the
> square of the distance.
It also scales linearly with the aperture radius, I guess? Then
you'd quickly get into very bulky lasers if you want to expand
the reach. But on a planetary surface, your horizon isn't going
to be too many kilometers away anyway. For anti-aircraft lasers,
two-meter tubes might be feasible.
> Another idea is to use a plasma window.
That sounds very cool... and very opaque. And somewhat
turbulent...
> For a laser, where you do not need vacuum for beam
> propagation, such a plasma window might be adequate to keep out dust,
> mist, rain, twigs, gnats, and the occasional curious hamster when the
> shutter is open.
A twig has such a small cross-section that it would have to push
against the plasma very, very lightly to be comparable to a 1 bar
atmosphere. =P
> One solution would be to use light of significantly longer wavelength
> than about 1 micron, since the materials of the eye are opaque to
> these wavelengths. I believe, for example, that 1.5 micron light is
> eye safe. Unfortunately, the longer the wavelength, the less tightly
> you can focus your laser at any given distance. Using light with a
> wavelength shorter than that which is passed by the eye probably will
> not work, since this will be absorbed by the atmosphere as well.
Well, some UV is absorbed by ozone, but we don't have much of that
down here, right? And some UV frequencies ionize oxygen, as shown
by the laser-taser concept. Furthermore, the UV frequency used
for the laser-taser is eye-friendly. How bad would the
attenuation be for non-ionising UV frequencies?
> Longer
> wavelengths tend to get through aerosols with a small particle size
> better than shorter wavelengths, so using eye-safe 1.5 micron IR or
> longer wavelengths might be an advantage in bad seeing conditions.
> This is not true, however, when the particle size gets to be about the
> same size or larger than the wavelength of the light you are using.
For rain drops, longer wavelengths would again be better, since
they'd be diffracted less strongly. Then again, a rain drop is
pretty strongly curved, so it would diffract most of the incident
light anyway.
> In addition, when laser beams enter the self focusing regime, I recall
> hearing that they are able to get through clouds much better than
> non-self focusing beams. In conditions of poor seeing, it might be
> best to focus your beam to a self focusing beam before you start to
> get significant attenuation. The self focusing beam looses energy
> continuously due to the formation of plasma as it propagates, but it
> can propagate for hundreds of meters. When the plasma losses are
> smaller than the losses due to beam scattering, this may end up being
> the preferred route.
Plasma? You mean it would glow and go "tyoo!" just like in the
movies? (=D
This self-focusing sounds pretty awesome. Got any website for
dummies about it? Any idea how bad the losses are?
> I expect you would use many mirrors in the optical path.
Wouldn't that make the whole thing very bulky? A 10 cm caliber
rifle would be somewhat awkward if it had a 5 m resonator folded
into it. =P
>>>I have not read these, I'm afraid. What was cold light?
>>
>>You haven't missed much... cold light was a banned radiation
>>weapon that caused a radioactive mess wherever it hit. It
>>sounds pretty much like what you said about electron beams.
>
>
> Ah. Got it. It is slightly better in this case, though, as electron,
> x-ray, or gamma ray beams do not leave lingering radioactivity,
I don't know whether it left lingering radioactivity, but it was
very hard to shield against, and unless you got a really heavy
dose, you'd die relatively slowly but unstoppably. That's why
it was banned as inhumane.
I seem to remember a scene where they transplanted a survivor's
brain into a brain-dead patient's body to get a few answers
about the attackers from him before he died. =P
> I'm not really sure what it takes to modify the FAQ for this list,
> though. I've occasionally thought about writing up my thoughts on
> beam weapons, because I seem to answer the same questions a lot.
> However, often intelligent questions or comments in the resulting
> discussions prompt me to think more about the subject, and so I learn
> something, too.
You can always update your FAQ entry when you learn something
new. ;-)
pervect
"Erik Max Francis" <m...@alcyone.com> wrote in message
news:3F5E93CA...@alcyone.com...
> Ray Drouillard wrote:
>
> > It's the old particle/wave duality. In recent experiments, scientists
> > have gotten atoms to interfere with each other like light waves.
>
> That only makes sense at very low temperature. If you're talking about
> plasma that's coming out of a weapon, it's hardly likely to be amenable
> to Bose-Einstein condensation.
>
> It's simply technobabble, so trying to extract meaning from it is a
> waste of time.
While I agree with your main point, IIRC one of the interesting things about
the molecular beam interference experiments was that the beams were NOT in
the ground state, so they did not even vaguely resemble a BEC. The quantum
numbers were in the thousands as I recall (vaguely). Interference still
happened even with the high quantum numbers, though.
pervect
"John Park" <af...@FreeNet.Carleton.CA> wrote in message
news:bjtas0$9qc$1...@freenet9.carleton.ca...
> If this works for the laser optics, why wouldn't it work for armour?
IIRC high reflective dielectric mirrors work only at one frequency. If your
opponent uses a mixture of different frequency lasers, your armor will work
only a small percentage of the time. The layer on top will be crucial - if
its the wrong frequency, it absorbs the energy, and the local explosion from
the energy will tend to damage the mirrors below it.
Ray Drouillard
"Anton Sherwood" <ne...@ogre.nu> wrote in message
news:vm4fede...@corp.supernews.com...
> JWMeritt wrote:
> > I personally find it interesting that a rifle is one of the very
few
> > products that, when used as directed, is INTENDED to kill people.
...
>
> Not true: guns are used far more often to influence someone's behavior
> than to kill him. Perhaps you meant `when activated'.
It all depends on where they are being used.
In the hot spots of the world, guns often used to kill, but are just as
often used to influence behavior.
In most other places, guns are used mainly to influence behavior.
In America, guns are used for recreation (target shooting), hunting, and
influencing behavior. Actually killing someone seems to come a distant
fourth.
Ray Drouillard
Luke
> Luke wrote:
>
> > Consider if you are swinging your laser at 1 radian per second. This
> > corresponds to an angular spread in the pulse train of 1 milliradian
> > in the one millisecond it takes to emit. At 100 meters, this
> > corresponds to a total spread of 10 cm.
>
> Well, 1 radian per second is pretty freaking huge. At that range,
> it would mean for the target to go at 100 m/s -- about twice as
> fast as your average freeway speeding ticket earner.
I was thinking more about if you were swinging your hand held laser to
engage a target with a "snap shot".
> > However, if the surface is highly reflective, the electronics that
> > estimate the target's distance and angular velocity could be fooled by
> > the reflections, resulting in a beam with little penetration.
>
> A neat effect, except that you'll also gleam in the sun like a
> christmas tree.
True, and show up like a beacon on radar.
> >>How does the spot size scale up when I increase distance for a
> >>constant aperture?
> >
> > The spot radius scales linearly with distance (see my first post in
> > this thread). This means the intensity falls off as one over the
> > square of the distance.
>
> It also scales linearly with the aperture radius, I guess? Then
> you'd quickly get into very bulky lasers if you want to expand
> the reach. But on a planetary surface, your horizon isn't going
> to be too many kilometers away anyway. For anti-aircraft lasers,
> two-meter tubes might be feasible.
Well, the spot size goes as 1/(aperture radius). So yeah, to strike
at targets several kilometers away you'd need an aperture about a
meter wide. Note also that the more energy per pulse you deliver, the
wider your spot can be and still give you explosive effects when the
beam is incident. Also, the more energy per pulse, the wider your
spot can be in order to focus down to the self focusing regime. So,
while a 1 joule pulse laser might be able to strike at several
kilometers with a 1 meter mirror, if you bump the energy per pulse up
to 100 joules, you can strike at targets 10 times farther away
(sqrt(100)=10). Spacecraft may want 3 to 10 meter mirrors for missile
defense or orbital engagements, but for most planetary forces a meter
wide aperture and hundreds of Joules per pulse ought to work at any
reasonable range.
> > Another idea is to use a plasma window.
>
> That sounds very cool... and very opaque. And somewhat
> turbulent...
Opaqueness really depends on the density of the plasma. A low density
plasma will be transparent to visible and near IR radiation. I think
the helium plasma was fairly low density in this application.
Obviously, you would want to get laminar flow in your plasma and the
surrounding gas.
> > For a laser, where you do not need vacuum for beam
> > propagation, such a plasma window might be adequate to keep out dust,
> > mist, rain, twigs, gnats, and the occasional curious hamster when the
> > shutter is open.
>
> A twig has such a small cross-section that it would have to push
> against the plasma very, very lightly to be comparable to a 1 bar
> atmosphere. =P
True. What I am wondering is what the thermal effects on the gnats,
twigs, and hamsters would be. Of course, you probably really do not
want soot getting on your mirror.
> > One solution would be to use light of significantly longer wavelength
> > than about 1 micron, since the materials of the eye are opaque to
> > these wavelengths. I believe, for example, that 1.5 micron light is
> > eye safe. Unfortunately, the longer the wavelength, the less tightly
> > you can focus your laser at any given distance. Using light with a
> > wavelength shorter than that which is passed by the eye probably will
> > not work, since this will be absorbed by the atmosphere as well.
>
> Well, some UV is absorbed by ozone, but we don't have much of that
> down here, right? And some UV frequencies ionize oxygen, as shown
> by the laser-taser concept. Furthermore, the UV frequency used
> for the laser-taser is eye-friendly. How bad would the
> attenuation be for non-ionising UV frequencies?
In a perfectly clear atmosphere, a photon of 0.4 micron violet light
will travel 25 kilometers on average before scattering. The rate of
scattering goes up as the fourth power of the frequency (or
conversely, as the inverse of the fourth power of the wavelength), so
a photon of 0.3 micron UV would be scattered from the beam on average
in 8 km, and a 0.2 micron UV photon would be scattered from the beam
on average every 1.5 km. The performance gets worse if there is haze
or other aerosols. Much below 0.2 microns, you get severe single
photon ionization.
The ionized oxygen and nitrogen used in the laser taser come from
multi-photon ionization, a process which is non-linear in the beam
intensity and generally requires a failry intense beam. For a low
intensity beam, those frequencies will not ionize the air
significantly. At a certain point, however, each UV photon will pack
enough energy to knock an electron from the molecular orbitals in
atmospheric gases - at that point the distance the beam will travel is
measured in meters or centimeters and UV becomes essentially useless
as a weapon in the atmosphere.
> > Longer
> > wavelengths tend to get through aerosols with a small particle size
> > better than shorter wavelengths, so using eye-safe 1.5 micron IR or
> > longer wavelengths might be an advantage in bad seeing conditions.
> > This is not true, however, when the particle size gets to be about the
> > same size or larger than the wavelength of the light you are using.
>
> For rain drops, longer wavelengths would again be better, since
> they'd be diffracted less strongly. Then again, a rain drop is
> pretty strongly curved, so it would diffract most of the incident
> light anyway.
Long wavelengths will _diffract_ more from raindrops, but will
_refract_ less. (With all the usual caveats about being somewhat near
an absorption line, which also does funny things to the index of
refraction).
> > In addition, when laser beams enter the self focusing regime, I recall
> > hearing that they are able to get through clouds much better than
> > non-self focusing beams. In conditions of poor seeing, it might be
> > best to focus your beam to a self focusing beam before you start to
> > get significant attenuation. The self focusing beam looses energy
> > continuously due to the formation of plasma as it propagates, but it
> > can propagate for hundreds of meters. When the plasma losses are
> > smaller than the losses due to beam scattering, this may end up being
> > the preferred route.
>
> Plasma? You mean it would glow and go "tyoo!" just like in the
> movies? (=D
That would be cute. It would certainly glow. Oddly enough, more of
the "glow" is scattered backwards towards the laser of forward toward
the target than to the sides. This might help the gunner train his
beam on a target (assuming a high pulse repetition rate) while making
it difficult for observers to tell where the beam is coming from -
unless you happen to be the target, of course.
> This self-focusing sounds pretty awesome. Got any website for
> dummies about it? Any idea how bad the losses are?
The losses can be estimated from claims that a single self focusing
"fillament" of light will propagate for several hundred meters.
Assume that it propagates for 200 meters. Then after 100 meters, it
will have lost roughly half of its energy. Fillaments do wierd
things, though, in that if they have too much energy, they split into
several parallel fillaments, and if they get too weak, they coalesce
into fewer, more energyetic fillaments. This would tend to give more
of an exponential decay with a characteristic falloff distance on the
order of a hundred meters or so.
I got lost of hits when I googled on light fillament ultrashort. Most
of these looked fairly technical, but you could poke around and see if
there was anything written for a popular audience.
> > I expect you would use many mirrors in the optical path.
>
> Wouldn't that make the whole thing very bulky? A 10 cm caliber
> rifle would be somewhat awkward if it had a 5 m resonator folded
> into it. =P
The resonator would probably only be a few tens of centimeters.
Assuming good material science, you might get away with the aperture
of the _resonator_ being only a couple centimeters across. Make the
adaptive optics a couple of centimeters across as well, and have the
laser propagate through a zig-zag path with a relatively short "zig"
and "zag" path length so that the beam does not diverge much over this
total path length. The last few mirrors will be wider to handle the
diverging beam before it is passed to the final beam pointer mirror.
I expect you could probably get away with only one pass of the beam
parallel to the resonator that goes the full resonator length - the
rest would be handled in a relatively short section involving multiple
mirrors, or by the zig zagging beam going back "above" the resonator
(assuming the resonator was parallel to the ground" just once while
bouncing off many mirrors in this path. Perhaps some ASCII art would
help:
|\|\|\|\|\|\\|\------------------
'-(-----------)
The parentheses are the resonator mirrors. All other mirrors were
omitted for clairity - just assume that wherever the beam changes
direction there is an appropriate mirror. The dashes, backslashes,
and other approximately line-like marks show the beam path. The beam
exits in the upper right, and is shown propagating some distance into
the atmosphere. Needless to say, with this many reflections, you can
get the beam going pretty much any direction you want it to by the
time it emerges.
Luke
Joseph Hertzlinger
<mferg...@cox.net> wrote:
> Christian Thalmann wrote:
>> Indeed. I meant coherent as in phase-locked, not condensed.
>> Atom-lasers. Bose-Einstein beams.
>
> Um, you were thinking of "atom lasers" as weapons?
>
> Alistair Reynolds' _Revelation Space_ mentions "boser"
> weapons that sound like that; I s'pose if it meant "boson
> amplification by stimulated emission of radiation" it should
> be "baser" but that sounds weird.
I have been wondering about the possibility of alpha-ray lasers.
Lasers can operate because photons are bosons and are susceptible to
Bose--Einstein condensation in which macroscopic quantities of bosons
are in the same quantum state. Alpha rays are also bosons. If
alpha-ray lasers are possible, then we could make all the nuclei in a
milligram of uranium discharge simultaneously in the same direction.
That would make a powerful particle-beam weapon. Larger amounts could
be used as a high-ISP rocket.
Getting the details right may be tricky...
Erik Max Francis
> I have been wondering about the possibility of alpha-ray lasers.
> Lasers can operate because photons are bosons and are susceptible to
> Bose--Einstein condensation in which macroscopic quantities of bosons
> are in the same quantum state. Alpha rays are also bosons. If
> alpha-ray lasers are possible, then we could make all the nuclei in a
> milligram of uranium discharge simultaneously in the same direction.
And then their net charge would cause them to repel each other in very
short order. Even neutral particle beams will spread due to thermal
effects.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Miles and miles and miles.
\__/ Alan Shepard (on the Moon)
Christian Thalmann
> Joseph Hertzlinger wrote:
>
>
>>I have been wondering about the possibility of alpha-ray lasers.
>>Lasers can operate because photons are bosons and are susceptible to
>>Bose--Einstein condensation in which macroscopic quantities of bosons
>>are in the same quantum state. Alpha rays are also bosons. If
>>alpha-ray lasers are possible, then we could make all the nuclei in a
>>milligram of uranium discharge simultaneously in the same direction.
>
>
> And then their net charge would cause them to repel each other in very
> short order. Even neutral particle beams will spread due to thermal
> effects.
Not to mention that the range of an alpha particle in air is
a few centimeters.
Mark Fergerson
> Joseph Hertzlinger wrote:
>
>
>>I have been wondering about the possibility of alpha-ray lasers.
>>Lasers can operate because photons are bosons and are susceptible to
>>Bose--Einstein condensation in which macroscopic quantities of bosons
>>are in the same quantum state. Alpha rays are also bosons. If
>>alpha-ray lasers are possible, then we could make all the nuclei in a
>>milligram of uranium discharge simultaneously in the same direction.
Neutral Helium would be better, methinks.
> And then their net charge would cause them to repel each other in very
> short order. Even neutral particle beams will spread due to thermal
> effects.
Hum. If the beam is truly coherent in the BEC sense, I
don't see why there'd be any inherent thermal effects.
OTOH I assumed you meant "thermal effects" to mean
transverse velocity components of the composite particles;
if you meant due to interaction with air or whatever, never
mind. Keeping the beam (pulse?) cold enough to _be_ a BEC
while getting it out of the weapon will be a challenge;
Reynolds handwaves a "laser confinement beam" for his bosers.
OTGH, exactly how fast could a coherent matter beam be
made to travel, muzzle-velocity-wise?
Mark L. Fergerson
Erik Max Francis
> Hum. If the beam is truly coherent in the BEC sense, I
> don't see why there'd be any inherent thermal effects.
>
> OTOH I assumed you meant "thermal effects" to mean
> transverse velocity components of the composite particles;
> if you meant due to interaction with air or whatever, never
> mind. Keeping the beam (pulse?) cold enough to _be_ a BEC
> while getting it out of the weapon will be a challenge;
> Reynolds handwaves a "laser confinement beam" for his bosers.
The problem here is that lasers, Bose-Einstein condensates, and
coherence are being banded about in ways that are not entirely
consistent. Normal photon lasers are coherent, but that doesn't mean
that they don't experience beam spread. (In fact, coherent just means
the photons are all in sync, it has little to do with collimation.)
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Youth is a period of missed opportunities.
\__/ Cyril Connolly
Stephan Aspridis
>
> Plasma? You mean it would glow and go "tyoo!" just like in the
> movies? (=D
>
If you want an energy weapon with these effects, you might want to take
a look at Gauss-Weapons. I recently saw an interesting demonstration in
TV. Apparently, NASA uses a railgun (which is _several_ meters long,
mind you) to accelerate 5mm aluminium pellets to about 10km/s. Needless
to say, at these speeds the pellets burn up from atmospheric friction,
but the white hot molten "bullet" leaves a neat glow. They use this
assembly to simulate asteroid impacts on a very small scale (with nasty
effects, as at these speeds, even a small pellet has the energy of a
large bore rifle - and would leave a rather nasty wound, as hypersonic
projectiles in general leave wounds that resemble the "shotgun at
point-blank" type).
regards,
Stephan
Mark Fergerson
> Mark Fergerson wrote:
>
>
>> Hum. If the beam is truly coherent in the BEC sense, I
>>don't see why there'd be any inherent thermal effects.
>>
>> OTOH I assumed you meant "thermal effects" to mean
>>transverse velocity components of the composite particles;
>>if you meant due to interaction with air or whatever, never
>>mind. Keeping the beam (pulse?) cold enough to _be_ a BEC
>>while getting it out of the weapon will be a challenge;
>>Reynolds handwaves a "laser confinement beam" for his bosers.
>
>
> The problem here is that lasers, Bose-Einstein condensates, and
> coherence are being banded about in ways that are not entirely
> consistent. Normal photon lasers are coherent, but that doesn't mean
> that they don't experience beam spread. (In fact, coherent just means
> the photons are all in sync, it has little to do with collimation.)
I agree completely. However the process that causes beam
spread in lasers doesn't seem to me to be applicable to a
hypothetical boser using massive bosons. The latter _will_
suffer from it if transverse velocity isn't zero for all
particles which ISTM it will be in a "properly prepared" BEC.
Can we get all our hands waving in synch here? ;>)
Mark L. Fergerson
Andrew Plotkin
>
> Can we get all our hands waving in synch here? ;>)
The Bozo-Usenet Condensate -- a group of newsgroup posters in perfect
synchronization -- has long been theorized to be possible, but all
attempts to create such a state have failed miserably...
--Z
"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
*
* Make your vote count. Get your vote counted.
MikeyD
> projectiles in general leave wounds that resemble the "shotgun at
> point-blank" type).
You mean shredding a large region of tissue? Or just in terms of the amount
of damage. I'd imagine (not being a biologist) that a small, fast pellet
would simply leave a hole the size of the pellet, along with some
shock/compression damage (bruising, maybe burst blood vessels) to the
surrounding tissue.
Karl M Syring
The damage is done by the fragmentation of the bullet, not by
the mythical "shockwaves", see
http://home.snafu.de/l.moeller/military_bullet_wound_patterns.html
Karl M. Syring
Luke
> If you want an energy weapon with these effects, you might want to take
> a look at Gauss-Weapons. I recently saw an interesting demonstration in
> TV. Apparently, NASA uses a railgun (which is _several_ meters long,
> mind you) to accelerate 5mm aluminium pellets to about 10km/s. Needless
> to say, at these speeds the pellets burn up from atmospheric friction,
> but the white hot molten "bullet" leaves a neat glow.
Well, technically it is compressional shock heating, and the glow is
plasma from the shock heated air and the surface of the projectile,
but anyway ...
> They use this
> assembly to simulate asteroid impacts on a very small scale (with nasty
> effects, as at these speeds, even a small pellet has the energy of a
> large bore rifle - and would leave a rather nasty wound, as hypersonic
> projectiles in general leave wounds that resemble the "shotgun at
> point-blank" type).
Interestingly, at these velocities the projectile has enough kinetic
energy to completely vaporize itself upon impact, plus a considerable
amount of the target. The net resut is that you get a flash of plasma
from the collision, which expands violently creating a shockwave -
similar to the explosive effects of pulsed lasers discussed elsewhere
in this thread. Unlike the laser pulses, however, the vaporized
material has momentum in the direction the projectile was moving, and
the superheated gases and, later, recondensed bits of the projectile
and target can still punch through the target by the simple method of
this jet pushing the material of the target aside, similar in some
ways to a thumbtack being driven into drywall. Unlike a thumbtack,
the jet tends to disperse fairly rapidly. The faster the projectile
moves, the greater the ratio of the energy to the momentum, the
quicker the jet disperses, and thus the more the blast from the impact
comes to dominate over the penetrating jet of material. In the limit
of super-high velocities, the effect of the impact of the projectile
will be essentially indistinguishable from the effect of a laser pulse
of the same energy incident upon the target.
One problem is that when I tried to estimate the range of a projectile
moving fast enough to glow through atmospheric shock heating, the
results were rather dismal at earth's atmospheric density for
projectiles packing about a rifle bullet's worth of kinetic energy. I
seem to recall the range was in the high tens of meters at around 5 to
6 km/s. This would be suitable for sidearms, but not for the
applications met by today's rifles.
Luke
John Schilling
>Christian Thalmann wrote:
Are you sure? NASA has never been one of the big players in railgun
research. And while they do have a couple of gadgets that launch small
projectiles at ~10 km/s, the ones I know of are light gas guns, not
railguns.
Stephan Aspridis
>
> Are you sure? NASA has never been one of the big players in railgun
> research. And while they do have a couple of gadgets that launch small
> projectiles at ~10 km/s, the ones I know of are light gas guns, not
> railguns.
>
Now that you mention it...
Sure I am not. I _am_ sure that the device was a couple of meters long,
that the pellets were made of aluminium and around 5mm diameter and that
about 10km/s was the muzzle velocity. It is quite possible that this was
essentially a large air-gun, but frankly, it's been quite a while and it
doesn't matter much for the effects.
regards,
Stephan
Stephan Aspridis
> The damage is done by the fragmentation of the bullet, not by
> the mythical "shockwaves", see
> http://home.snafu.de/l.moeller/military_bullet_wound_patterns.html
>
Not at these velocities. I checked the article and it's about supersonic
bullets like the 5.56mm and the 7.62mm. At velocities of several km/s
other rules apply which mainly can be summarized with "impact crater and
an energy to momentum ratio sufficient to vaporize the projectile
involved (unless made of tungsten or the like)"
regards,
Stephan
Luke
One issue is that bullets from modern rifles are subsonic in tissue
(they are certinaly supersonic in air, however). These hypervelocity
pellets would be supersonic in tissue. Thus, while modern rifle
bullets will not cause a shock wave in tissue (a compression wave and
expanding cavity, certainly, but not a true shock) the pellet would.
It is not clear that this would necessarily lead to increased tissue
destruction, however. Shockwaves from explosions are known to lead to
pulmonary hemmorhaging and ruptured bowels, a shock from a hypersonic
pellet might do the same. The extreme stretching of the tissue in the
vicinity of the projectile's passage could also lead to increased
tearing. On the other hand, shockwaves lose energy to heating as they
propagate - this could lead to less energy being put into mechanical
disruption than with a bullet. Energetically, mechanical disruption
is two to three orders of magnitude more efficient at damaging tissue
than heating, so the development of a shock might well be
counterproductive.
Luke
Karl M Syring
Yeah, but you must make a cut of somewhere, I would think, it
is 2 km/s, which seems to be the upper limit for conventional
chemical guns.
Karl M. Syring
Mark Fergerson
> Mark Fergerson wrote:
>
>
>> Hum. If the beam is truly coherent in the BEC sense, I
>>don't see why there'd be any inherent thermal effects.
>>
>> OTOH I assumed you meant "thermal effects" to mean
>>transverse velocity components of the composite particles;
>>if you meant due to interaction with air or whatever, never
>>mind. Keeping the beam (pulse?) cold enough to _be_ a BEC
>>while getting it out of the weapon will be a challenge;
>>Reynolds handwaves a "laser confinement beam" for his bosers.
>
>
> The problem here is that lasers, Bose-Einstein condensates, and
> coherence are being banded about in ways that are not entirely
> consistent. Normal photon lasers are coherent, but that doesn't mean
> that they don't experience beam spread. (In fact, coherent just means
> the photons are all in sync, it has little to do with collimation.)
BTW, boser weapons look slightly less improbable- I just
found:
http://www.ifi.unicamp.br/goq/news.html
(look for "A CONTINUOUS ATOM LASER BEAM" about 4/5 of the
way down) about continuous atom-laser beams focusable to a 1
nm radius. Also mention of the free beam having a spread of
"a tenth of a degree, comparable to a laser pointer".
So, a little scaling-up, something like Hershcovitch's
snazzy new "plasma window" for ordinary particle accelerators:
http://www.bnl.gov/bnlweb/pubaf/pr/2001/bnlpr121101b.htm
(commercial version, yet!)
to extract the beam, and Presto!, the boser is born!
Mark L. Fergerson
Luke
1.5 km/s is about the speed of sound in tissue. This varies according
to different tissue types, of course, but 1.5 km/s is typical except
for bone (which is about 4 km/s).
At 2 km/s nearly anything will be badly fragmented (tungsten
anti-armor projectiles possibly excepted), but vaporization does not
set in until you get to about 4 km/s.
I don't think there really is any sharp cutoff, more of a gradation
from puncture wound to tissue badly shredded by multiple fragments to
explosive effects.
Luke
Erik Max Francis
> BTW, boser weapons look slightly less improbable- I just
> found:
>
> http://www.ifi.unicamp.br/goq/news.html
>
> (look for "A CONTINUOUS ATOM LASER BEAM" about 4/5 of the
> way down) about continuous atom-laser beams focusable to a 1
> nm radius. Also mention of the free beam having a spread of
> "a tenth of a degree, comparable to a laser pointer".
There's nothing in physics that prevents you from building neutral
particle beams. However, that doesn't mean that they don't suffer from
beam spread just like normal lasers.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Possibilities travel / Endless through infinity
\__/ Chante Moore
Mark Fergerson
> Mark Fergerson wrote:
>
>
>> BTW, boser weapons look slightly less improbable- I just
>>found:
>>
>>http://www.ifi.unicamp.br/goq/news.html
>>
>> (look for "A CONTINUOUS ATOM LASER BEAM" about 4/5 of the
>>way down) about continuous atom-laser beams focusable to a 1
>>nm radius. Also mention of the free beam having a spread of
>>"a tenth of a degree, comparable to a laser pointer".
>
>
> There's nothing in physics that prevents you from building neutral
> particle beams. However, that doesn't mean that they don't suffer from
> beam spread just like normal lasers.
Fine, we agree. What I can't figure out how to figure out
is a comparison of beam spreading between "conventional"
(incoherent) and coherent neutral particle beams, especially
after it leaves the hardware (for now I'm happy to ignore
handwaved "containment laser beam" complications).
Any ideas?
Mark L. Fergerson
pervect
"Mark Fergerson" <mferg...@cox.net> wrote in message
news:3F6896CE...@cox.net...
> Fine, we agree. What I can't figure out how to figure out
> is a comparison of beam spreading between "conventional"
> (incoherent) and coherent neutral particle beams, especially
> after it leaves the hardware (for now I'm happy to ignore
> handwaved "containment laser beam" complications).
>
> Any ideas?
If you assume that there is no interaction between the neutral particles of
your beam, you can use the approximation Eric gave earlier to calculate the
Maxwell-boltzman velocity in the transverse direction based on the
temperature of the beam.
The temperature of actual beams will almost certainly be many times higher
than the ultimate limiting temperature of a beam in a BEC state. I would
approximate the temperature of the later very roughly by taking a single
particle of the beam, and putting it in a "box" (square well potential)
which is the size of the beam. The ground state energy of this "particle in
a box" can be found by the formulas at
http://www.wikipedia.org/wiki/Particle_in_a_box#The_Particle_in_a_1-dimensio
nal_Box
basically h^2/8m (9nx/lx)^2 + (ny/ly)^2 + (nz/lz)^2)
where for the ground state, lx=ly=1
If you like your temperature in degrees, you have to do the appropriate unit
conversion from energy units to temperature units using Boltzman's constant.
This is extremely crude just to get the right order of magnitude. A more
rigorous analysis would realize that there is no box, but would assume some
sort of beam profile which satisfies Schrodinger's equation (I think a
gaussian function would work), and would get the transverse velocity
directly from the beam "size". But I expect that the two results will agree
within an order of magnitude or so.
It's quite likely that there will be some interaction between the neutral
particles of the beam, however, due to for example Van der Waals forces.
These inter-particle forces can actually hold your particle beam together.
This can potentially be done even at high temperatures, much higher than the
temperature of a BEC. A time honored application of the use of Van der
Waals forces to hold particle beams together is, as mentioned earlier, the
bullet or arrow.
All in all, it seems much more achievable to make your particle beam cool
enough to hold together via Van der Waals forces than it does to chase the
idea of putting the particle beam in the ultimately lowest temperature state
it can have, which for beams of macroscopic size would require nanokelvin
temperatures. [I haven't worked out the approximate temperature of a 1
micron^2 aperture beam by the above "particle in a box" formula, but I would
expect it to be somewhere in the nanokelvin range].
pervect
> Now that you mention it...
>
> Sure I am not. I _am_ sure that the device was a couple of meters long,
> that the pellets were made of aluminium and around 5mm diameter and that
> about 10km/s was the muzzle velocity. It is quite possible that this was
> essentially a large air-gun, but frankly, it's been quite a while and it
> doesn't matter much for the effects.
Just a quick note. The problem with conventional guns is that you start to
hit a barrier when you get bullet speeds near the speed of sound of the
atmosphere. You just can't get the bullet to travel much faster than the
propagation speed of a shockwave in your working gas.
Replacing the air with a gas with a lighter molecular weight (hydrogen is
the best) helps get around this physical limit. Hence the "light gas gun".
It's farily conventional in that you use an explosive to compress the gas to
propel the bullet. The difference is that you use a gas other than air.
There's a lot more info on the internet if you (or anyone who isn't already
familiar with it) is interested.
Erik Max Francis
> Fine, we agree. What I can't figure out how to figure out
> is a comparison of beam spreading between "conventional"
> (incoherent) and coherent neutral particle beams, especially
> after it leaves the hardware (for now I'm happy to ignore
> handwaved "containment laser beam" complications).
My point is that you keep saying _coherent_, which has nothing to do
with _collimation_. Coherent just means that the photons (as of a laser
beam) are all in phase; I'm not even sure the term as it stands has
relevance to Bose-Einstein condensates. Furthermore, coherence has
nothing to do with collimations, since laser beams are coherent but that
does not make them more or less collimated.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Life imitates art far more than art imitates life.
\__/ Oscar Wilde
Luke
> A time honored application of the use of Van der
> Waals forces to hold particle beams together is, as mentioned earlier, the
> bullet or arrow.
I think these are bound by stronger forces, metalic chemical boding in
the case of bullets, hydrogen bonding and covalent bonding in the case
of arrows. Most materials held together primarily by Van der Waals
forces are gases at room temperature.
Luke
pervect
"Luke" <lwca...@uci.edu> wrote in message
news:e9134b72.03091...@posting.google.com...
How sure are you about that? I'm not terribly certain myself, but my
recollection was that covalent bonds held together molecules
(intramolecular), while molecules interacted (intermolecular) by Van der
Waals forces (and maybe some electric dipole interactions).
Even if you were right, and if one insisted on using Van der Waals forces
rather than other avilable forces between the particles in the beam, the
resulting temperature would still be hotter (and easier to achieve) than a
BEC if it was only in the region of the temperatures required to liquify
gasses.
IIRC the BEC's mentioned in the literature had temperatures in the tens to
hundereds of nanokelvin, the temperature of the BEC was determined by the
size of the magnetic "box" they were confined to which IIRC again was in the
micron range. (An ambitous person could work through the formulas I
mentioned to compute the ground state energy given the box size, I haven't
done that to check my memory though).
A bigger box means a lower ground state and a lower temperature required to
form a BEC.
Luke
> Coherent just means that the photons (as of a laser
> beam) are all in phase; I'm not even sure the term as it stands has
> relevance to Bose-Einstein condensates.
It does. Matter has a wavelength equal to hbar/(2 pi * momentum).
The atoms in a condensate are all in the same quantum state, so they
have the same wavelegth and are in phase with each other.
As you mention, though, they are not necessarily collumated.
Luke
Luke
> "Luke" <lwca...@uci.edu> wrote in message
> news:e9134b72.03091...@posting.google.com...
> > "pervect" <perv...@netscape.net> wrote in message
> news:<m12ab.57622$Qy4.8610@fed1read05>...
> > > A time honored application of the use of Van der
> > > Waals forces to hold particle beams together is, as mentioned earlier,
> the
> > > bullet or arrow.
> >
> > I think these are bound by stronger forces, metalic chemical boding in
> > the case of bullets, hydrogen bonding and covalent bonding in the case
> > of arrows. Most materials held together primarily by Van der Waals
> > forces are gases at room temperature.
>
> How sure are you about that? I'm not terribly certain myself, but my
> recollection was that covalent bonds held together molecules
> (intramolecular), while molecules interacted (intermolecular) by Van der
> Waals forces (and maybe some electric dipole interactions).
I know that metals are sort of one big giant molecule. The atoms all
share electrons, making each electron state sort of one big covalent
bond extending over the whole metal. Hydrogen bonds are the primary
thing holding water together (as well as ammonia and hydrogen
fluoride), and they are important for other molecules where you have
electronegative atoms bonded to hydrogen - like most biological
molecules. Also, for keratin or cellulose or the other large
biological molecules you've got making up the arrow they tend to bond
to each other and also loop around each other making a big tangled
mess that is hard to pull apart.
Hydrogen bonds are an interaction between permanent electric dipoles.
This makes them fairly strong. You can also have polarization
interactions, where a permanent dipole induces a dipole in the
surrounding medium. These are not as strong. Van der Walls
interactions are even weaker because they come from two objects
without permanent dipoles - fluctuations in their electric charge
distribution makes temporary dipoles, and the temporary dipole of one
molecule can induce a dipole in a neighboring molecule, binding the
two molecules loosely together.
> Even if you were right, and if one insisted on using Van der Waals forces
> rather than other avilable forces between the particles in the beam, the
> resulting temperature would still be hotter (and easier to achieve) than a
> BEC if it was only in the region of the temperatures required to liquify
> gasses.
True. It would also be denser than a condensate. You'd need to have
essentially liquid densities. There's nothing wrong with using a high
velocity cryogenic stream of liquid as a weapon, however. At high
enough velocity, it is bound to seriously mess up a person's innards.
Luke
Mark Fergerson
> Erik Max Francis <m...@alcyone.com> wrote in message news:<3F68EB1B...@alcyone.com>...
>
>>Coherent just means that the photons (as of a laser
>>beam) are all in phase; I'm not even sure the term as it stands has
>>relevance to Bose-Einstein condensates.
>
>
> It does. Matter has a wavelength equal to hbar/(2 pi * momentum).
> The atoms in a condensate are all in the same quantum state, so they
> have the same wavelegth and are in phase with each other.
It's a little early in the morning, but...
I mentioned transverse velocity in re: beam dispersion
because in a BEC (or atom laser beam), all the particles are
in the same state(s), hence if you want to deflect one of
them, you have to deflect _all_ of them (from the referenced
article).
> As you mention, though, they are not necessarily collumated.
Huh? How could they _not_ be in an atom laser beam?
I _said_ it was early.
Mark L. Fergerson
pervect
> True. It would also be denser than a condensate. You'd need to have
> essentially liquid densities. There's nothing wrong with using a high
> velocity cryogenic stream of liquid as a weapon, however. At high
> enough velocity, it is bound to seriously mess up a person's innards.
I was thinking more of space applications. You'd have trouble keeping the
cyrogenic liquid cyrogenic passing through an atmosphere. Not as much of a
problem as you would of keeping a BEC a BEC passing through an atmosphere,
but it'd still be impractical.
I was hoping to get away with less than liquid densities to get some
self-attraction, but if that's what you need, I guess that's what you need.
I haven't attempted to put any numbers to the idea.
pervect
> It does. Matter has a wavelength equal to hbar/(2 pi * momentum).
> The atoms in a condensate are all in the same quantum state, so they
> have the same wavelegth and are in phase with each other.
>
> As you mention, though, they are not necessarily collumated.
I just can't see any advantage to having them in the same quantum state,
except for light.
With light, IIRC you can get around the radiance theorem by having a
coherent beam. This came up in the usenet discussions of heating an object
up via sunlight hotter than the surface of the sun. You can't do it with
passive optics (mirrors) because the radiance theorem prohibits one from
focusing the spot to a small enough size. It is possible if you convert the
sunlight into a laser beam.
[Unless I misunderstood the point of the discussion, I should add, but
that's the way I recall the argument going.]
But with a matter beam, you are not going to gain the same focusing
advantages. When your particles of matter get close enough, they are still
going to interact in the normal way. A BEC has to be diffuse enough for the
matter not to interact to qualify as a BEC - otherwise it'd be a small solid
or liquid particle and not a BEC.
The wavelength of any reasonable matter particle is smalle enough that I
don't see how you could possibly gain any advantage from avoiding the
radiance theorem before you ran into the particle-particle interaction limit
(for any massive boson, anyway).
pervect
> I mentioned transverse velocity in re: beam dispersion
> because in a BEC (or atom laser beam), all the particles are
> in the same state(s), hence if you want to deflect one of
> them, you have to deflect _all_ of them (from the referenced
> article).
Actually, the way I would put it, if you interact with a BEC strongly enough
to deflect a particle, you remove that particle from the BEC.
If you did want to keep the BEC a BEC, you'd have to interact with all of
the particles uniformly.
To put it another way, BEC's can expand. I recall some of the early
experiments. They'd create the BEC in a magnetic "box". [I'm not sure if
you can create a BEC without some sort of "box" - I suspect you can't, but I
don't have that written on an engraved tablet.] When you put the particles
in the box, and cool them so that every particle is in the ground quantum
state of the box, you have a BEC. (Assuming the particles are they right
sort so they don't interact and condense, anyway).
The experimenters released the box, and the BEC expanded. They would let it
expand for a while, then they'd take a picture of it with a flash of laser
light. Taking the picture would interact strongly enough to destroy the
BEC.
The point is that BEC's can expand and remain BEC's. So if you go to the
rest frame of your proposed BEC beam, you can also see it expand.
Back to the main point. Now, I'm not sure how detailed the pictures they
took actually were (I'd have to re-read the article). As I recall they were
looking for anisotropic expansion - the thing that makes the BEC expansion
different from thermal expansion is that the velocity profile depends on the
shape of the box it was in. If the box is not uniform in size, the BEC will
expand in different directions at different rates. This is utterly
different than how normal thermal expansion happens (the later is isotropic
regardless of the shape of the box).
You were interested in the expansion rate - when you start out in a box (I
think your BEC beam launcher will have to qualify as a box), you can compute
the velocity profile from Schrodinger's equation. The bigger the box, the
colder the BEC, and the lower the velocity profile. But this is just
another way of saying that large BEC's are colder (even tiny micron sized
ones are in the tens-hundereds of nanokelvin region, as I menitioned
earlier).
Conceptually, when you "take a picture", you find that every atom in the
ex-BEC has a definite location, and they are all different locations.
Similarly, if you took a "velocity picture", you'd find that they all had
different velocities. But until you took the picture, you could treat them
as if they were all the same. It's the usual quantum weirdenss - like
schrodinger's cat, when you open the box, you find what you'd expect, either
a live cat, or a dead one. You never find a half-alive, half-dead cat. You
can think of this as if the wavefunction collapses when you make the
measurement, though that's not the particular interpretation of quantum
mechanics that I actually subscirbe to. So until you "take a picture", you
can think of all the particles as being the same. When you interact
strongly enough to localize all the particles, you destroy the BEC-ness of
the BEC, and you see for all appearances a collection of perfectly normal
particles.
Luke
> > Erik Max Francis <m...@alcyone.com> wrote in message news:<3F68EB1B...@alcyone.com>...
> >
> >>Coherent just means that the photons (as of a laser
> >>beam) are all in phase; I'm not even sure the term as it stands has
> >>relevance to Bose-Einstein condensates.
> >
> >
> > It does. Matter has a wavelength equal to hbar/(2 pi * momentum).
> > The atoms in a condensate are all in the same quantum state, so they
> > have the same wavelegth and are in phase with each other.
>
> It's a little early in the morning, but...
>
> I mentioned transverse velocity in re: beam dispersion
> because in a BEC (or atom laser beam), all the particles are
> in the same state(s), hence if you want to deflect one of
> them, you have to deflect _all_ of them (from the referenced
> article).
`Fraid not. Scattering is probabalistic in quantum mechanics. Take
an ideal laser beam. All the photons are in the same QM wave
function. Yet, they can still scatter independantly off of
particulates, obstructions, or whatever is in th beam path.
There can be a minimum energy needed to scatter a particle in a BEC.
This is what gives superconductors their zero resistance and
superfluids their zero viscosity. In a BEC, this energy will be very
low (on the order of Boltzman's constant times the critical
temperature), so low that the kinetic energy of the particles in the
beam will be considerably higher than this at any reasonable velocity.
Hence, any interaction with, say, atmospheric gases will tend to
scatter particles out of the BEC.
> > As you mention, though, they are not necessarily collumated.
>
> Huh? How could they _not_ be in an atom laser beam?
A wave function can be expanding. Drop a rock into the water. Watch
the ripples. They expand outward. The ripples are a classical wave
function. QM wave functions are similar. The area with
non-negligible probability density can be expanding, contracting, or
more or less holding the same spread. In a freely propagating wave,
however, there are strict limits on how well the wave can converge, or
for how long it can remain more or less as spread out as it was
earlier. Afterwards, the wave must begin to expand. This is as true
of QM waves as it is of classical ones.
A BEC of atoms may all be in the same wavefunction, but if that
wavefunction is expanding, the BEC beam will not be collumated. If it
initially collumated, it will eventualy reach a point where it must
start to spread out.
Luke
Kai Henningsen
> Mark Fergerson <mferg...@cox.net> wrote in
> news:3F5B057D...@cox.net:
>
> > Christian Thalmann wrote:
> >> Stephan Aspridis wrote:
> >>
> >>> Paul Ciszek wrote:
> >>>
> >>>> As far as Coherent matter beams go, the military has had
> >>>> some success with weapons that use Fermi exclusion forces
> >>>> to accelerate a "pulse" of Quantum-entangled baryons and
> >>>> leptons.
> >
> > Wait; that describes everything from nuclear bombs to
> > black-powder cannon!
>
> I think it can be stretched to include bows and arrows also.
What do you have against throwing stones? That was a great high-tech
advantage over fists and teeth!
Kai
--
http://www.westfalen.de/private/khms/
"... by God I *KNOW* what this network is for, and you can't have it."
- Russ Allbery (r...@stanford.edu)
Earl
news:8uFwn...@khms.westfalen.de:
> nep...@wt.net (Earl) wrote on 07.09.03 in
> <Xns93EFA050...@205.230.159.13>:
>
>> Mark Fergerson <mferg...@cox.net> wrote in
>> news:3F5B057D...@cox.net:
>>
>> > Christian Thalmann wrote:
>> >> Stephan Aspridis wrote:
>> >>
>> >>> Paul Ciszek wrote:
>> >>>
>> >>>> As far as Coherent matter beams go, the military has
>> >>>> had some success with weapons that use Fermi exclusion
>> >>>> forces to accelerate a "pulse" of Quantum-entangled
>> >>>> baryons and leptons.
>> >
>> > Wait; that describes everything from nuclear bombs to
>> > black-powder cannon!
>>
>> I think it can be stretched to include bows and arrows
>> also.
>
> What do you have against throwing stones? That was a great
> high-tech advantage over fists and teeth!
>
> Kai
Stones would not qualify unless you are including sling
throwers.
The requirement was for a weapon that accelerates a pulse.
A stone would not qualify unless you include the human as the
"weapon" or use a sling. The stone is only the "pulse", not the
weapon.
Lucius Chiaraviglio
> Luke wrote:
>> I can't think of any way to keep a plasma at significantly greater than
>> atmospheric pressure from exploding as soon as it is no longer confined
>> by your weapon, nor have I been able to come across any literature
>> describing way of doing so.
>
> You can find literature explaining why it's not possible. Key phrase:
> 'virial theorem'.
Not sure if this could work, but how about this: instead of keeping
all of the energy as pressure, keep most of it stored in an electric
current and magnetic field internal to the plasma bolt. If I understand
correctly, the electric current and its magnetic field can be configured
to constrict the plasma bolt in 2 axes and expand it in the axis parallel
to its direction of motion (can't get rid of expansive force in at least
one axis). Due to induction, the current will persist for some time (just
how long would be a limit on range). Then you hit the plasma bolt from
behind throughout its flight with a laser beam at a frequency that is very
strongly absorbed by the particular plasma you are using (but not by air,
because absorption of the acceleration laser by air will limit your
range); the absorbed energy ablates some ions off the back of the plasma
bolt and produces acceleration that opposes the part of the magnetic force
trying to expand the plasma bolt longitudinally (how long you can do this
before you ablate the entire plasma bolt is another limit on range). You
could even fine-tune the aim of the laser to produce slightly off-axis
ablation to steer the plasma bolt if something was trying to dodge it.
Damage to the target comes from a combination of sudden quenching of the
internal electric current and magnetic field, the kinetic energy of the
plasma bolt, the heat and pressure stored in the plasma, and the
absorption of energy from the acceleration laser on the tail end of
explosion of the plasma bolt. Range is limited by whichever is worst of
the 3 range-limiting effects described above.
--
Lucius Chiaraviglio
Approximate E-mail address: luci...@chapter.net
To get the exact address: ^^^ ^replace this with 'r'
|||
replace this with single digit meaning the same thing
(Spambots of Doom, take that!).
Lucius Chiaraviglio
> Christian Thalmann <cingaDo...@gmx.net> wrote in message
> news:<3F604056...@gmx.net>...
>> Luke wrote:
>> > There are ways to magnetically confine plasmas, but these rely on
>> > electrical currents that run axially or circumferentially to the
>> > plasma stream. I cannot think of any way to get even transient
>> > currents through the atmosphere at long distances to confine the
>> > plasma.
>>
>> Couldn't currents in the plasma create a magnetic bottle for itself?
>
> If you have circumferential currents, the plasma will squirt out the ends.
> You can't have axial currents, because there needs to be a return path.
> A more complicated arrangement might work, but ...
How about either ground return (for a weapon on a fixed installation) or
twin plasma conduits (for a vehicle-mounted weapon -- one has current
coming and one has current going)? Of course, electrostatic attraction
and magnetic repulsion might not cancel, and might leave a varying
residual force between the plasma conduits or the plasma conduit and
ground, which would play havoc with any attempt to aim the weapon over
substantial distances -- this might only be suitable for a short range
weapon with substantial diffused damage, looking a good bit like a
Protoss Archon in action in Starcraft. :-)
Lucius Chiaraviglio
> A suit of armor with the thickness and composition of rifle-barrel steel
> would be proof against ordinary rifle bullets; that doesn't make the rifle
> a useless weapon. Same principle here.
Sure about that? The rifle barrel doesn't have to take the impact of a
bullet hitting it at right angles, but rather the force needed to contain
the rapidly expanding (subsonic) gas used to propel the bullet. If a
bullet from another rifle of the same type hit at right angles, it might
be bad. (So would jamming the bullet in the barrel right before firing
the charge.)