Pulse laser preliminary recognition
David
I would like to ask if there is a way to recognize your laser has
output pulse? I mean, how to distinguish with your eyes or low cost
equipment that your laser emit pulse, not CW? Because I heard that the
laser meter has two kind: power meter and energy meter. We must know
exactly the output regime to use the correct meter, right? If using
the wrong meter, it maybe damaged and huge money will be lost.
And if the laser is pulse, can we estimate it Joule and pulse width,
repetition rate to safely choose the detector head?
So anyone can give a hint?
Lostgallifreyan
edcab1...@12g2000pri.googlegroups.com:
Sweep the output across a wall, look for a dotted line. If you see one, try
using a moving mirror to get regular and repeatable sweeps. That way you have
what amounts to a crude oscilloscope and can make better judgements.
For power, on the cheap, a thermoelectric cooler painted black will output
volts to a millivolt meter. Make sure the TEC is mounted on a big thick
heatsink, and shrouded against ambient heat hitting the black painted side.
You'll need to calibrate with a known continuous-wave output laser of at
least 100 mW to get any accuracy worth having, but this will get you within
around 5% if your reference laser is accurately known. You could pay a lot of
money (several hundered bucks at least) to get better than 5% accuracy. A
black painted TEC is good enough for twenty watts or more if the coating and
heatsinking are good, and unless the laser pulse is very short and very hard,
even a DIY paint job will last long enough to give you useful data.
Lostgallifreyan
news:Xns9CAC2CA4C1F...@216.196.109.145:
> David <choose...@gmail.com> wrote in news:7b69c810-1786-4c5f-8f62-
> edcab1...@12g2000pri.googlegroups.com:
>
>> Hi everyone,
>> I would like to ask if there is a way to recognize your laser has
>> output pulse? I mean, how to distinguish with your eyes or low cost
>> equipment that your laser emit pulse, not CW? Because I heard that the
>> laser meter has two kind: power meter and energy meter. We must know
>> exactly the output regime to use the correct meter, right? If using
>> the wrong meter, it maybe damaged and huge money will be lost.
>> And if the laser is pulse, can we estimate it Joule and pulse width,
>> repetition rate to safely choose the detector head?
>> So anyone can give a hint?
>>
>
> Sweep the output across a wall, look for a dotted line. If you see one,
> try using a moving mirror to get regular and repeatable sweeps. That way
> you have what amounts to a crude oscilloscope and can make better
> judgements.
>
Also, if you have an infrared laser (for example, a green DPSS that hasn't
got proper filtering on it, or one designed to emit IR..) this trick still
works. Just observe the drawn line through a digital camera viewfinder. In
the case of the faulty DPSS you'll need to try filtering the visible light
out to be sure that what you see is IR because if the colour saturates to
white you'll likely not tell the difference in the image.
David
> Lostgallifreyan <no-...@nowhere.net> wrote innews:Xns9CAC2CA4C1F...@216.196.109.145:
>
>
>
> > David <choosersl...@gmail.com> wrote in news:7b69c810-1786-4c5f-8f62-
> > edcab16f6...@12g2000pri.googlegroups.com:
>
> >> Hi everyone,
> >> I would like to ask if there is a way to recognize your laser has
> >> output pulse? I mean, how to distinguish with your eyes or low cost
> >> equipment that your laser emit pulse, not CW? Because I heard that the
> >> laser meter has two kind: power meter and energy meter. We must know
> >> exactly the output regime to use the correct meter, right? If using
> >> the wrong meter, it maybe damaged and huge money will be lost.
> >> And if the laser is pulse, can we estimate it Joule and pulse width,
> >> repetition rate to safely choose the detector head?
> >> So anyone can give a hint?
>
> > Sweep the output across a wall, look for a dotted line. If you see one,
> > try using a moving mirror to get regular and repeatable sweeps. That way
> > you have what amounts to a crude oscilloscope and can make better
> > judgements.
>
> Also, if you have an infrared laser (for example, a green DPSS that hasn't
> got proper filtering on it, or one designed to emit IR..) this trick still
> works. Just observe the drawn line through a digital camera viewfinder. In
> the case of the faulty DPSS you'll need to try filtering the visible light
> out to be sure that what you see is IR because if the colour saturates to
> white you'll likely not tell the difference in the image.
Thanks for your hints.
I thought that you were saying about pulse lamp-pump laser, right?
Such laser has repetition rate at 2Hz and of course sweeping it
against a wall can see the dotted line.
Here I would like to say about Q-switch laser with repetition rate
about kHz or more, and narrow pulse width, like the laser Q-switch
with Cr:YAG or GaAs..
Your way of using a TEC has a large time constant due to the heat
transfer between the black paint layer and the TEC, right? If we plug
it into a digital multimeter, can it measure high repetition
frequency? Or we have to use a osilloscope?
Lostgallifreyan
98f2f3...@a37g2000prf.googlegroups.com:
> On Oct 22, 10:28�am, Lostgallifreyan <no-...@nowhere.net> wrote:
>> Lostgallifreyan <no-...@nowhere.net> wrote innews:Xns9CAC2CA4C1F6Dzoodlew
> ur...@216.196.109.145:
I was thinking of those DPSS lasers that claim CW while actually using pulses
at a repeat rate fast enough to look like CW till you try to scan it..
The TEC itself will have a large time constant, larger than the black paint
itself, but if what you're after is the average power of a source that might
be pulsed, the method is ok.
One way to check for fast pulses with an expendable cheap part is a PIN
photodiode, those will catch very short pulses and be cheap enough that
blowing a few up will be painless. :)
If you have a repeat rate in KHz (I always capitalise that K, as it's a
multiple, not a fraction, it seems to fit convention better that way..) and a
short Q-switched pulse, then just drawing the beam across a safely placed bit
of wall should show it. It would look like a series of very sharply defined
dots. At which point a PIN photodiode might be the next easiest and cheapest
way to assess the pulse energy before risking expensive equipment.
You'll likely get better answers than mine if you hang around a while..
DougD
Well, in the case of say a q-switched YAG, you can pretty much
audibly hear that you're running in pulse mode! I had a need to
calibrate the rep rates on a YAG marker, and needed a way to
know the rep rate without having to tap into the electronics to
look at the q-switch drive signals. So, I just took a cheap
microphone and hooked it to the inputs on my analog scope
and then let the mic pick up the sound of the beam as it was
scanned over say sheet metal under the marking head. It
was very easy, and obvious to tell from the waveforms on
the scope the frequency of the q-switch, as well as getting
some idea of pulse duration, and even first pulse suppression,
etc. It's not the most scientific method to do these measurements,
but on the other hand it is inexpensive, un-obtrusive to the laser,
and accurate as long as you stay within the freq. response of
the microphone.
d.
David
Thanks Lostgallifreyan
Assume that the laser head illuminates a mirror rotating with speed
180 degree/0.1sec, and the mirror is 2 m far away from the wall of a
circle house, then according to you, we will see, in 0.1 sec, about
10.000 light spot from a 100kHz pulse laser ( i saw kilogram was
abbreviated kg, not Kg, so I'm familiar with this notation). By that
time your image of beam from the mirror travels 3.14/2x2m=3.14m, then
each spot light will be 3.14m/10.000= 314 um away from each other.
I mean if using your way, we will see a series of light dots which are
31.4micromet from each other. If our output beam diameter is about
2mm, then I doubt we can see a series of light dots, but a light line.
However, for a pulse laser at 100Hz, then the spacing between light
dots will be 31.4mm, quite large. Damn my high repetition rate laser.
To Doug: your way seems very interesting, but I didnot totally get it.
You mean that illuminating a pulse laser at a metal sheet will make
sound? I heard that Nd:YAG has lower repetition rate, about kHz, and
if there is sound from the metal sheet then the sound will be in the
range between 20Hz and 20 kHz, human hearing threshold. And then you
hook your microphone to the PC and open a program of recording sound
having spectrum analyzer, right?
Because I'm working with intracavity green laser, I though simply that
with the same pump power, then the green beam will be stronger for
pulse laser, right? Becasue conversion efficiency increase with
intensity, and Q-switch laser must have intensity of 1064 m laser much
stronger than cw regime?
Lostgallifreyan
e3243e...@12g2000pri.googlegroups.com:
> Assume that the laser head illuminates a mirror rotating with speed
> 180 degree/0.1sec, and the mirror is 2 m far away from the wall of a
> circle house, then according to you, we will see, in 0.1 sec, about
> 10.000 light spot from a 100kHz pulse laser ( i saw kilogram was
> abbreviated kg, not Kg, so I'm familiar with this notation). By that
> time your image of beam from the mirror travels 3.14/2x2m=3.14m, then
> each spot light will be 3.14m/10.000= 314 um away from each other.
> I mean if using your way, we will see a series of light dots which are
> 31.4micromet from each other. If our output beam diameter is about
> 2mm, then I doubt we can see a series of light dots, but a light line.
> However, for a pulse laser at 100Hz, then the spacing between light
> dots will be 31.4mm, quite large. Damn my high repetition rate laser.
>
I hadn't calculated it that accurately. :) I was working ona memory of an
LED drive actually, I had a 3.5 KHz drive and a duty cycle of between 100:1
and 10:1 off:on timing. I wanted to detect the pulsed light when I turned my
head or moved the source swiftly, but for it to look continous when
stationary. By that reckoning, I assumed a moving mirror could be easily set
up to emulate this for Khz rates.
WHat you can try is the really cheap scanner method of gluing a small plane
mirror roughly perpedicular on the end of a small motor spindle, so an
incident beam draws a circle of fixed radius at a fixed distance. It's very
easy, cheap, can be set to any speed within a wide range, and safely limits
the circle to a size small enough to find safe ways to aim a beam on a
modest-sized target for viewing. You'll likely find a combination of speed
and distance that will give you a clean projection revealing the pulse
quality to some extent.
> To Doug: your way seems very interesting, but I didnot totally get it.
> You mean that illuminating a pulse laser at a metal sheet will make
> sound? I heard that Nd:YAG has lower repetition rate, about kHz, and
> if there is sound from the metal sheet then the sound will be in the
> range between 20Hz and 20 kHz, human hearing threshold. And then you
> hook your microphone to the PC and open a program of recording sound
> having spectrum analyzer, right?
>
That's how I interpreted it. It's a nice idea. I don't work with lasers
strong enough to try this, but I do have one thing (small YAG) which will let
me try it, if I ever get round to building a PSU and trigger for it...
> Because I'm working with intracavity green laser, I though simply that
> with the same pump power, then the green beam will be stronger for
> pulse laser, right? Becasue conversion efficiency increase with
> intensity, and Q-switch laser must have intensity of 1064 m laser much
> stronger than cw regime?
>
Doug's idea might work for that, though I suspect you'll need to use black
paper to get the best chance of a good noise. :) I think you're right about
the efficiency improving, to the point where it might be audible in its
effect on thin black paper (ink ablation) but calculating output will be a
royal pain, and might best be measured by averaging from the integrating
response on a thermopile meter, then do a scan to see what kind of duty cycle
you're getting, and back-calculate from those observations rather than try to
predict it from any reading of input pump power.
DougD
>To Doug: your way seems very interesting, but I didnot totally get it.
>You mean that illuminating a pulse laser at a metal sheet will make
>sound? I heard that Nd:YAG has lower repetition rate, about kHz, and
>if there is sound from the metal sheet then the sound will be in the
>range between 20Hz and 20 kHz, human hearing threshold. And then you
>hook your microphone to the PC and open a program of recording sound
>having spectrum analyzer, right?
Yes, that's about how it works. Of course, you have to have enough power
to interact with the sheet metal, etc. However even a YAG marker, etc.
at low power will still make some acoustic noise on paper, just at very
low levels, probably lower than the background noise level of the
equipment. I typically use a 50 or 75 watt YAG marker, and anywhere
from 20% to full power, the beam will make a significant amount of
acoustic interaction with a metal substrate. And yes, the q-switch in
most markers run from the 20-20Khz range. You can use a mic and
sampling software in a computer, I just used a plain old analog
oscilliscope to display the mic output. I have a newer smart scope
that will display freq. and time measurements on it's own, so that's
why I chose that method. I do have to use cursor measuring though
as the acoustic pulse has more of a square or sawtooth shape,
where the auto measurement is only really accurate on sine waves.
It has been useful though for debugging some problems that were
driving me crazy that I could not figure out by visual means. I could
see extra pulses that the software were supposed to suppress that
were not coming from the controlling computer, but because of a
flaw in the q-switch driver. If I were to have tried to diagnose the
RF output by use of a dummy load and scope, I would not have
seen the problem, it was coming from some ringing in the AO
device/connector/cable path, but I could "see it" acoustically..
d.
Lostgallifreyan
news:wdWdnZfOHN9EFnzX...@supernews.com:
> the beam will make a significant amount of
> acoustic interaction with a metal substrate
LOL, I like that. Reminds me of how a cricket ball can be bowled with results
that get called 'chin music'. If the commentators got wind of "a significant
amount of acoustic interaction" with the batsman, we'd never hear the end of
it. :)
andythemechanic
Nd:Yag, passively Q-switched, ~10kHz rep rate, 100mW average power. When
I aligned it with iris diaphragms I always heard the laser "singing"
when I closed the iris too much. :-)
DougD schrieb:
George Herold
Hi David, I'd just use a small area photodiode, and (maybe) 50 ohm
resistor across it. Look at the voltage signal on an oscilloscope.
(As Lostgallif... suggested.)
Choose the resistor as a balance between signal and speed... larger
R’s will give more signal (up to a point) but slower response time.
You can calculate the response time of the circuit if you know the
capacitance of the photodiode (PD) (tau = RC) (listed on the PD spec
sheet.) If this is still not fast enough you can reverse bias the
diode with a 9V battery and reduce the photodiode C by maybe a factor
of 4 or 5.
George H.
DougD
>The TEC itself will have a large time constant, larger than the black paint
>itself, but if what you're after is the average power of a source that might
>be pulsed, the method is ok.
>
>One way to check for fast pulses with an expendable cheap part is a PIN
>photodiode, those will catch very short pulses and be cheap enough that
>blowing a few up will be painless. :)
>
>If you have a repeat rate in KHz (I always capitalise that K, as it's a
>multiple, not a fraction, it seems to fit convention better that way..) and a
>short Q-switched pulse, then just drawing the beam across a safely placed bit
>of wall should show it. It would look like a series of very sharply defined
>dots. At which point a PIN photodiode might be the next easiest and cheapest
>way to assess the pulse energy before risking expensive equipment.
>
>You'll likely get better answers than mine if you hang around a while..
>
Actually, what would probably make a fairly good sensor for higher powers,
and also high freq. components would be a very thin stack of Terfanol(tm).
This stuff is just amazing, I used it as part of the talking straw thing as a
form of beam modulator, and the guys that make this material up for
commercial end use have made stacks up to 100khz. It's a doped iron
magnetoconstricive material that is(was?) owned by the US Navy as
they developed it for hull mounted phased array sonar stacks to replace
the old piezo materials. It was still classified up until the 80s, then
commercialized by a company in Iowa who I made a point of becoming
"best friends" with at one point. Haven't dealt with them now for about 10
years, but I bet a .5 inch diameter by maybe 1/16 thick bit could be had
dirt cheap, and that stuck inside a simple coil would make a nice sensor
that could stand high powers, yet produce high freqency signal response
on pulsed beams.. Now if I could only get my own stack back from a
certain person in the film biz that I "borrowed" it to, I could test this
out... You hear me Jeff?!!!
Oh, and that stuff was highly export controlled, could still be the case for
non-finished raw materials of any sig. amount. I do know where it can
be purchased as a finished product though and then a sensor could be
reverse engineered out of it... Also, you can make pretty damn good
scanners out of the stuff..
d.
STEVE ROBERTS
WTF are you smoking. You have NO idea about how to test a high powered
laser.
OPTICAL SAFETY IS PARAMONT>
You DO NOT spray light around the room from QSWITCHED OR PICO or
FEMTO ANYTHING.
To the OP, what is the make and model of your laser? We can tell you
much from that.
The key words here are pickoff sampler and high speed photodiode with
a oscilloscope.
In rare cases at far IR a small piezo will do just fine.
Steve
Lostgallifreyan
e60b82...@g23g2000vbr.googlegroups.com:
From David's first post:
>> >> I would like to ask if there is a way to recognize your laser has
>> >> output pulse? I mean, how to distinguish with your eyes or low cost
>> >> equipment that your laser emit pulse, not CW?
From one of mine, where I accounted for one of my answers:
"I was thinking of those DPSS lasers that claim CW while actually using
pulses at a repeat rate fast enough to look like CW till you try to scan
it.."
Steve, if you read the points I quote above you'll see why I said what I did.
David seemed to be asking about a laser whose output was meant to be viewed
and that he had seen it, i.e. a show laser, or DPSS pointer, or other modest
source that was ambiguous, meant to be CW but possibly not. At the time I
posted my response he had not mentioned Q-switching or any high power system,
and with such systems the question of CW or pulse is rarely ambiguous.
If you want to get smart you need to BE there. I did what I could because no-
one else was there to answer at the time. I also made it clear that better
answers were likely, eventually. If you have them, just get on with it.
STEVE ROBERTS
> If you want to get smart you need to BE there. I did what I could because no-
> one else was there to answer at the time. I also made it clear that better
> answers were likely, eventually. If you have them, just get on with it.
Lovely little logical fallacy. You advise a beginner to do something
inherently unsafe.
Yet it is OK for you to do so :
1. Because no other person with experience is there at the moment.
2. Its ambiguous , therefore he is safe.
Wrong of you to do. We are our brother's keeper. You cannot post such
advice without mentioning the safety protocols.
Once upon a time I ran a test. I posted a Standard Laser Warning
sign for a 60 watt average power, Qswitched 7 nS Class IV laser on a
lab door and installed the rotating warning light. The sign was very
clear and huge. It clearly had a sign below saying laser installed,
in operation when light is on, ring phone before entering. 2 full
professors and 20 some graduate students came barging in the door or
used a master key to open the door, disrespecting the warning. All of
them found themselves getting a refresher course in reading signs.
You cannot assume the person on the other end always knows what they
are doing, they came to you for advice and you offered it, they assume
you know what you are doing.
Clearly you need to rethink your attitude to radiation safety.
Steve
David
Hi Steve
Currently I have not made or acquired any pulse laser, but is trying
to make one. I'm trying to make a green DPSS Q-switch laser: Nd:YVO4,
Cr:YAG To=85% and OC mirror (HR1064 HT532).
At first I will try using a 1W laser 808nm to make it lase. I think it
can lase with threshold below 1W, because the initial transmission of
Cr:YAG is rather high. I read a paper that an intracavity plano-
concave resonator like that will have threshold at 240mW. At 600mW
pumping, the output is: average power 56mW, pulse with 28.4ns,
repetition rate 118.2kHz, peak power 16.7W.
I have a thick cloth surrounding our laser area, and the laser area is
so small that it can only accommodate two people. And I wear safety
goggles for 1064, 808 and 532nm.
Thus I think the method Lostgallifreyan told is not safe, but with low
output like that is there a problem?
What I would like you guy to help me is not to measure exactly and
quantitatively the parameter of such laser, but to recognize whether
the laser is in pulse mode and estimate roughly the energy, pulse
repetition rate... to choose a suitable detector (or ND filter) so
that the detector will not be damaged.
Lostgallifreyan
>> If you want to get smart you need to BE there. I did what I could
>> because no- one else was there to answer at the time. I also made it
>> clear that better answers were likely, eventually. If you have them,
>> just get on with it.
>
> Lovely little logical fallacy. You advise a beginner to do something
> inherently unsafe.
>
> Yet it is OK for you to do so :
>
> 1. Because no other person with experience is there at the moment.
> 2. Its ambiguous , therefore he is safe.
>
> Wrong of you to do. We are our brother's keeper. You cannot post such
> advice without mentioning the safety protocols.
>
If you were here more often to take care of your brother laserists you might
know I'm usually a lot more careful than I was here in what I said, but I
take your point, it was ambiguous, and too full of assumptions, even though
they ARE actually good ones, foolish novices don't tend to barge in here, do
they? They go to the Laser Pointer Forums. Even if they do show, they stick
out like a sore thumb. And at this point they are looking at a computer
monitor, not at a laser, and I explicitly said wait for better advice, too..
I seem to recall several people posting recently who were actually new to
lasers, having found 40W CW YAG modules on eBay. Apart from advice to wear
goggles and point the thing at a brick and not get too close to the spot, I
didn't see a lot of advice on safety. So perhaps you ought to stick around if
you're that much more concerned with it that you need to sound off suggesting
another person knows nothing when they make one less-than-rigorous suggestion
that you take objection to.
STEVE ROBERTS
oscilloscope?
1064 nm is on the ragged edge of a silicon detector. However some mid
Ir detectors have gotten very cheap lately.
Second of all, not much if any doubling will occur unless the CR:Yag
is Qswitching.
How big is your pump diode? This will give me some clues about what
level to suggest for safety setups that allow you to view the green.
May I also assume that you will try IR first before inserting the
doubler crystal?
Some cheaper grades of short persistance zinc sulphide phosphor
extinguish when pumped by deep blue leds or uv light and hit by IR,
I've had good luck with that from Post Apple Scientific. The united
nuclear green phosphor on ebay does NOT quench.
So you aim your beam (expanded with a lens) at a phosphor screen and
you see a dark spot if the laser is working. This lets you work while
wearing goggles.
A few of the ebay Chinese Sr:YAG blue phosphors quench as well.
This would allow you to make something you can see while wearing yag
laser goggles. A black and white ccd camera (15$, Supercircuits.com)
will easily see the 808 pump, but most will not see small amounts of
1064.
IR viewing cards that work by upconversion are out there as well, this
place is expensive, you can find them cheaper with some work,
http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=296&pn=VRC2
Steve
David
I have two IR viewing card, one very sensitive but can not stand high
power, and one not very sensitive, but I think it can stand high
power. So viewing 1064 is not a problem.
I don't have oscilloscope. And I'm not familiar with using such to get
signal from Si photodiode. Can you tell me how to use an oscilloscope
and a photodiode to measure the pulse? Or can you suggest me webpage
mentioned about that?
As I said, I has one 1W laser 808nm. I will get a more powerful laser,
but I thoght 1W is enough for some basic pulse laser, right?
STEVE ROBERTS
place the photodiode into the beam, wire a 50 to 470 ohm resistor
across the photodiode to act as a load, connect the scope's probe
across the photodiode/load resistor combination. Keep all connections
as short as possible. The resistor has to be chosen for the light
level. It will respond to the 808 for sure, but it will show a
envelope response for the 1064 nm pulses , if there. If your pulses
were at a audio rate, the PD output could be ac coupled into a audio
amplifier or if a bit higher in frequency, a AM radio and you could
"hear" clicks and tones harmonicly related to the pulses. But that is
a really iffy way of doing it, the scope method is the method of
choice.
Odds of your generating enough power to "melt" a viewing card are low
to zero without focusing the beam at your pump power.
Is this a hobby project or a lab project? Next question is where are
you at, I know quite a network of EO technicians and Engineers and
hobbyists, many of whom can help you.
This will see one micron quite well and is very fast.
Try to find a copy of Phil Hobbs book. Phil hangs out at
sci.electronics.design, once you have the book.
http://www.electrooptical.net/
Building Electro-Optical Systems:,
Making It All Work, Second Edition
Steve
STEVE ROBERTS
photodiode or even a solar cell for the 808. Do you have safety
goggles?
A small CCD camera will see the 808 reflecting inside the laser
The pc302sx will work for you, it outputs NTSC, you will need a
monitor, a old tv with a video input, or a frame grabber for your
computer to use it.
Steve
George Herold
>
> Try to find a copy of Phil Hobbs book. Phil hangs out at
> sci.electronics.design, once you have the book.
>
> http://www.electrooptical.net/
>
> Building Electro-Optical Systems:,
> Making It All Work, Second Edition
>
>
> - Show quoted text -
All excellent, One thought I had was that since the pulses from the
photodiode are no more than 0.5 V or so in size, it's safe to couple
them into the audio input of a computer. There are lots of programs
out there that can turn the audio card into a cheap oscilloscope. As
long as the rep rate is below 40kHz??? Actually I don't know how fast
the audio cards are, certainly at least 20kHz.
George H.
Lostgallifreyan
286753...@i4g2000prm.googlegroups.com:
> There are lots of programs
> out there that can turn the audio card into a cheap oscilloscope. As
> long as the rep rate is below 40kHz??? Actually I don't know how fast
> the audio cards are, certainly at least 20kHz.
>
GoldWave is available as shareware so you can view a waveform in that. Unlike
Sound Forge (v4.5 anyway..) it allows zoom beyond the one pixel per sample
view. Also, there might be cheap USB inputs for sample rates up to 192 KHz to
be found on eBay. Audiophile ADC boxes.. Some might not easily allow
bypassing input capacitors so you could have a DC offset in the signal but
for short pulses it probably won't matter if the caps are still in place.
DougD
Years ago I needed to monitor the light output of a Lexel as well as monitor
the temp. of the etalon in it. I bought one of those cheap National a/d boxes
that ran on a serial port at that time (I'm guessing that it's all USB now),
and it worked great!! The bandwith was very high for a serial port, and
they had all sorts of app's for logging, etc. You could run it as a digital
strip chart recorder, set alarm points, trigger logging on setpoints, and
do basic scope functions. At the time I bought mine, Radio Shack in the
US was selling them as a catalog only purchase, I got mine direct from
National. Oh, forgot to mention that it came with it's own thermistor!
I think it had two analog in's and at least two digital in's, and I think some
dig out's.. All for under $120, maybe even lower.. Of course, that was
a few years ago...
Here's the webpage for the DAQ gizmo that I've got:
http://www.ni.com/dataacquisition/
d.
Lostgallifreyan
news:nOWdnQ0o64uOjHDX...@supernews.com:
> Years ago I needed to monitor the light output of a Lexel as well as
> monitor the temp. of the etalon in it. I bought one of those cheap
> National a/d boxes that ran on a serial port at that time (I'm guessing
> that it's all USB now), and it worked great!! The bandwith was very high
> for a serial port, and they had all sorts of app's for logging, etc. You
> could run it as a digital strip chart recorder, set alarm points,
> trigger logging on setpoints, and do basic scope functions.
That IS very impressive for serial.. If you mean serial as in RS232 at some
unusual fast rate, can you tell me more? I think of RS-232 in serial hardware
form as one of those things for which every obituary over the past decades
was premature, as will be those over the next decades too, so anything really
cool done with it interests me.
Btw, for logging stuff, Sparkfun Electronics now do a 'Logomatic v2'. Not
good for audio rates, well not beyond logging at a KHz or so anyway at best,
but it is a very amazing tool that I think anyone logging anything needs to
check oput.
Lostgallifreyan
firmware), serial isn't that fast, max is 115200 baud, though the logger
hardware and code do allow for nonstandard baud settings, so maybe faster
too.
DougD
>m...@here.com (DougD) wrote in
>news:nOWdnQ0o64uOjHDX...@supernews.com:
>
>> Years ago I needed to monitor the light output of a Lexel as well as
>> monitor the temp. of the etalon in it. I bought one of those cheap
>> National a/d boxes that ran on a serial port at that time (I'm guessing
>> that it's all USB now), and it worked great!! The bandwith was very high
>> for a serial port, and they had all sorts of app's for logging, etc. You
>> could run it as a digital strip chart recorder, set alarm points,
>> trigger logging on setpoints, and do basic scope functions.
>
>That IS very impressive for serial.. If you mean serial as in RS232 at some
>unusual fast rate, can you tell me more? I think of RS-232 in serial hardware
>form as one of those things for which every obituary over the past decades
>was premature, as will be those over the next decades too, so anything really
>cool done with it interests me.
>
Well, can't say that it was blinding fast, but for the type of logging that
I was trying to do, it was plenty fast. I was basically watching for mode hops
in a twin tube lexel that I was doing holography with. Even with the temp.
controlled etalon, and all sorts of environmental precautions (enclosed air
table, stable temp and humidity), it would hop every 5 minutes or so, and
would wreck any hologram made, so I set up the serial logger to give me
a display on a laptop that watched the light control sensor, as well as the
thermistor that I had tacked onto the etalon heater. Then I could tweak
the heater controls to min. the hops, as well as tell me when it was
"safe" to do an exposure. It was accurate enough that I could set limits
that could spot when it was moving towards the next hop, and eventually
I put that alarm loop in series with the shutter trigger so that I could load
the film, set the trigger, then walk away and the whole thing would just
wait for the laser to be stable and then trigger the shutter to open.. Did
I mention that I've been an automation junkie in a prior life?...
Oh, as for serial ports, they are typically slow, however I've known a
few guys that like programming right down to the machine code and
have forced serial bits to do things they were never intended for!
Most of the original show control hardware that runs the attractions
at Universal, Disney, etc. were triggered off of tons of serial ports
on networked control boxes made by one company out of Iowa
that made lowly PC's do things they were never intended to..
d.
Lostgallifreyan
news:ELKdnTixRIbD0nPX...@supernews.com:
> Well, can't say that it was blinding fast, but for the type of logging
> that I was trying to do, it was plenty fast. I was basically watching
> for mode hops in a twin tube lexel that I was doing holography with.
> Even with the temp. controlled etalon, and all sorts of environmental
> precautions (enclosed air table, stable temp and humidity), it would hop
> every 5 minutes or so, and would wreck any hologram made, so I set up
> the serial logger to give me a display on a laptop that watched the
> light control sensor, as well as the thermistor that I had tacked onto
> the etalon heater. Then I could tweak the heater controls to min. the
> hops, as well as tell me when it was "safe" to do an exposure. It was
> accurate enough that I could set limits that could spot when it was
> moving towards the next hop, and eventually I put that alarm loop in
> series with the shutter trigger so that I could load the film, set the
> trigger, then walk away and the whole thing would just wait for the
> laser to be stable and then trigger the shutter to open.. Did I mention
> that I've been an automation junkie in a prior life?... Oh, as for
> serial ports, they are typically slow, however I've known a few guys
> that like programming right down to the machine code and have forced
> serial bits to do things they were never intended for! Most of the
> original show control hardware that runs the attractions at Universal,
> Disney, etc. were triggered off of tons of serial ports on networked
> control boxes made by one company out of Iowa that made lowly PC's do
> things they were never intended to..
>
That's why I like them, the capacity to do things beyond original intent, it
makes them interesting, not just useful. I wish I knew C well... That SFE
Logomativ v2 board has ten ADC lines, two UARTS, and a decent MPU so the
thing can be set to 31.25 Kbaud and have two MIDO I/O channels and read
custom inputs at 12 bits, more than enough to make glitch-free MIDI controls,
and can be programmed to do event and message substitutions, delays, etc... I
mean, several hundreds of pounds worth of gear effectively emulated by
something that was never made with anything remotely close to that as design
or intent. Considering that each of those 10 ADC lines is on an 'IO' pin that
can just as easily be an output, I imagine a competent lasec scanner
controller even smaller than Pangolin's FB3 might be built from a Logomatic
board, by anyone who knows C, they barely need to know any electronics.
Going wildly off-topic perhaps, but given what that board might be put to it
doesn't have to be.
David
> m...@here.com (DougD) wrote innews:ELKdnTixRIbD0nPX...@supernews.com:
To Steve
I checked the PIN diode you mentioned, it has rise/fall time =4000
picosecond, is that the reason making it capable to measure laser
pulse?
And the area of it is rather small, 300um in diameter, which mean
there's no way to collect all laser beam to it, right? I think it is
used only to get part of the laser beam and then show the pulse width
and repetition frequency on oscilloscope, it give no information about
pulse energy.
Anyway, thank you for your hint. But why the setup so simple: just
connect the photodiode with a resistor and plug to a oscilloscope?
Sound very easy.
I see another photodiode on eBay:http://cgi.ebay.com/API-Photodiode-
PIN-Blue-Enchaced-laser-optics-10-
pack_W0QQitemZ180419733844QQcmdZViewItemQQptZLH_DefaultDomain_0?
hash=item2a01daa954
It has response from 300nm to 1100nm. And it has a curve of
responsitivity, unit A/W. If the setup is easy, I need only to connect
this diode to a multimeter and read the current flow through it, then
we have a laser power meter?
This is our small lab project currently, and I'm reading some meter on
Newport to find some laser power emter to measure power and laser
pulse. Too many things to learn and to choose :(
DougD
>That's why I like them, the capacity to do things beyond original intent, it
>makes them interesting, not just useful. I wish I knew C well... That SFE
>Logomativ v2 board has ten ADC lines, two UARTS, and a decent MPU so the
>thing can be set to 31.25 Kbaud and have two MIDO I/O channels and read
>custom inputs at 12 bits, more than enough to make glitch-free MIDI controls,
>and can be programmed to do event and message substitutions, delays, etc... I
>mean, several hundreds of pounds worth of gear effectively emulated by
>something that was never made with anything remotely close to that as design
>or intent. Considering that each of those 10 ADC lines is on an 'IO' pin that
>can just as easily be an output, I imagine a competent lasec scanner
>controller even smaller than Pangolin's FB3 might be built from a Logomatic
>board, by anyone who knows C, they barely need to know any electronics.
>
>Going wildly off-topic perhaps, but given what that board might be put to it
>doesn't have to be.
I'm somewhat embarrassed to admit this, but the first real laser scanner
controller I built for someone else to use was made around the original
Radio Shack (Tandy) notebook, I think it was a model 200 or 400?
It had an 8255 on this odd little opening in the bottom of thing, just like
they had put it there just for me!!! That gave me 3x 8 bit ports to work
from, and I was able to work around the internal Basic it came with
enough to get fairly fast cones/boxes, etc. out to a pair of D/A's and
then some on/off laser bits, and then a few left over for a couple of
beam positioners. It was kinda an ugly front end as it was only meant
to be a basic word processor, email thing that was coveted by news
reporters when it first came out, but I was able to make up some simple
menu's and beam/pattern select out of the function keys...I think it was
either a whopping 4 or 8mhz processor!! Back then it seemed everything
had those 8255's in them, and they were well documented, supported
in Basic, and easy to wire up!
d.
(just replaced the keyboard and of course it's gota stuck spacebar...)
grr., sorry..
Lostgallifreyan
news:ZZSdndBnqqsNsHLX...@supernews.com:
Not sure why you'd be embarassed. :) I never knew enough to even think of
doing that when I first got a ZX Spectrum, which ought to be similarly
capable. But I might benefit from what amounts to very low cost per machine
to play with some of the better old tech. Someone in the UK is selling a few
Hewlett Packard 200LX portables for �100 each. Not sure how good a deal that
is but they have an Intel 186 CPU and run pretty much any DOS program that
wasn't dedicated to accessing a hard disk. Given the size, that could be a
useful tool. All kinds of general purpose stuff might be done with that.
Having used an Organiser XP for many years, and having also used a Dell X50V
PDA, I think there are good reasons to go with the old gear. But I do think
�100 is a bit steep.. An X50V can be had for �60 or so... I'd definitely pay
�50 for a 200LX though, in good shape. But I'd need the machine for its use
as a kind of toolbox, not as a collectors item. Modern PDA's are too fragile
and power-hungry.
STEVE ROBERTS
communications, more then fast enough, and the laser is bright enough
that you will not have to focus it down on the the PD, its ok to just
interecept part of the beam.
And Dd and LGF, these days serial is dead, this is USB, 169$ and
comes with very capable signal express which exports to excel, has
chart recorder and scope mode, selectable triggering, allows process
control, waveform generation etc. The USB 6009 rocks for small signal
work.
http://sine.ni.com/nips/cds/view/p/lang/en/nid/14605
While it may or may not be fast enough for the OP's problem. A
picoscope is. www.picoscope.com
So would be a low end OWON scope these days.
Steve
Lostgallifreyan
9b34e9...@d21g2000yqn.googlegroups.com:
> And Dd and LGF, these days serial is dead, this is USB, 169$ and
> comes with very capable signal express which exports to excel, has
> chart recorder and scope mode, selectable triggering, allows process
> control, waveform generation etc. The USB 6009 rocks for small signal
> work.
>
Serial is dead for speed, but it's just cool. :) The more I use it the more I
like it (and it never seems to die, which is part of the fascination). But
$169 is a good price for what you describe. For that I wouldn't spend much
time agonising over coercing a sound based system to do it, even a costly
fast one won't be as good. But still worth a look for those who want 8 or 10
cheap channels of logging or control.
DougD
>And Dd and LGF, these days serial is dead, this is USB, 169$ and
>comes with very capable signal express which exports to excel, has
>chart recorder and scope mode, selectable triggering, allows process
>control, waveform generation etc. The USB 6009 rocks for small signal
>work.
>
>http://sine.ni.com/nips/cds/view/p/lang/en/nid/14605
Very cool!
As for the serial chatter, that was in reference to my last
exposure (no pun) hands on, of a cheap but useful data
interface. I would certainly hope that no one is going out
and making a point of trying to buy a serial interface over
a USB! And there's still tons of serial ported hardware out
there in daily use. Just like ion lasers, they may not be all
that practical anymore, but we shouldn't forget how to keep
them working just because they're out of style..
d.
Lostgallifreyan
dn...@supernews.com:
> I would certainly hope that no one is going out
> and making a point of trying to buy a serial interface over
> a USB!
What if is literally a serial interface over USB? :) Just playing devil's
advocate here, but it does bear thinking of, because the serial port profile
is one of the better established USB methods, certainly for Bluetooth
devices. Baud rates can go way high, and it's a very easy method to write
interfacing for. So we can have the best of both, the USB speed, and the
serial protocol. (Using xon/xoff flow control, ideally to save headaches).
This is just a thoughtful wander though, there are likely better ways to
exploit the USB buss especially if the hardware was intended do do so, or the
user knows how to code for it, but serial over USB might be a reliable
fallback plan, and it should be widely compatible so useful when making
things useful in ways not originally planned, which can be crucial for low-
cost lab work.
DougD
I wish I had a clever thought here, but like the weather outside, my brain
is in a fog today and taking the afternoon off...
d.
Lostgallifreyan
news:eMSdnYKHxcOACG3X...@supernews.com:
> I wish I had a clever thought here, but like the weather outside, my brain
> is in a fog today and taking the afternoon off...
>
Mine does that. Took me three days to locate a very small coding problem that
on hindsight is clearly related to stuff I read in two different places, and
now I can't remember where I read it so it might take me another three to fix
it...
Jürgen Appel
> Anyway, thank you for your hint. But why the setup so simple: just
> connect the photodiode with a resistor and plug to a oscilloscope?
Almost. For a decent speed I would use this circuit:
.-------.
The resistor deter- | |
mines the bandwidth | |
of the circuit, since | V <-
it forms a low pass |+ -
with the diode's --- |
capacitance. Smaller - o-----o
resistor=faster, | .-.
but your signal am- | |R|
plitude goes down | | | Measure here
proportionally. | '-'
| |
'-------o-----o
|
created by AACircuit v1.28.6 ===
GND
The battery voltage does not matter much, higher is better, since a higher
voltage decreases your diode's capacitance, but a too high voltage blows the
diode. A 9V block battery should be safe with almost all diodes I know, but
better check your data sheet (max. reverse voltage). Higher voltages also
give higher dark currents, but that should not matter since you are going to
shine bright light onto it anyway.
> It has response from 300nm to 1100nm. And it has a curve of
> responsitivity, unit A/W. If the setup is easy, I need only to connect
> this diode to a multimeter and read the current flow through it, then
> we have a laser power meter?
In principle, yes.
You have to make sure you don't saturate the diode, so you probably need a
set of attenuators (but you can calibrate them yourself, once you have your
setup going, so cheap ones will do). Up to 1 mW of power such a PIN diode
certainly should behave nicely linear if you don't focus the light too much.
Since your laser is pulsed, it might be worth noting that the speed of the
photo diode might be significantly slower than specified at wavelength
regions where the quantum efficiency is low (in your diode >950 nm).
Cheers,
Jürgen
Jürgen Appel
David wrote:
> Anyway, thank you for your hint. But why the setup so simple: just
> connect the photodiode with a resistor and plug to a oscilloscope?
Almost. For a decent speed I would use this circuit:
.-------.
The resistor deter- | |
mines the bandwidth | |
of the circuit, since | - <-
it forms a low pass |+ ^
with the diode's --- |
capacitance. Smaller - o-----o
resistor=faster, | .-.
but your signal am- | |R|
plitude goes down | | | Measure here
proportionally. | '-'
| |
'-------o-----o
|
created by AACircuit v1.28.6 ===
GND
The battery voltage does not matter much, higher is better, since a higher
voltage decreases your diode's capacitance, but a too high voltage blows the
diode. A 9V block battery should be safe with almost all diodes I know, but
better check your data sheet (max. reverse voltage). Higher voltages also
give higher dark currents, but that should not matter since you are going to
shine bright light onto it anyway.
> It has response from 300nm to 1100nm. And it has a curve of
> responsitivity, unit A/W. If the setup is easy, I need only to connect
> this diode to a multimeter and read the current flow through it, then
> we have a laser power meter?
In principle, yes.
David
Hi,
Could you send me the drawing again? Your circuit diagram is not
displayed correctly in this uneset group. Thanks
Lostgallifreyan
502b94...@u16g2000pru.googlegroups.com:
>> � � � � � � � � � � � .-------.
>> The resistor deter- � | � � � |
>> mines the bandwidth � | � � � |
>> of the circuit, since | � � � - <-
>> it forms a low pass � |+ � � �^
>> with the diode's � � --- � � �|
>> capacitance. Smaller �- � � � o-----o
>> resistor=faster, � � �| � � �.-.
>> but your signal �am- �| � � �|R|
>> plitude goes down � � | � � �| | � Measure here
>> proportionally. � � � | � � �'-'
>> � � � � � � � � � � � | � � � |
>> � � � � � � � � � � � '-------o-----o
>> � � � � � � � � � � � � � � � |
>> created by AACircuit v1.28.6 ==
>> � � � � � � � � � � � � � � �GND
>
> Hi,
> Could you send me the drawing again? Your circuit diagram is not
> displayed correctly in this uneset group. Thanks
>
>
It is, if you use a fixed width font.
George Herold
>
> - Show quoted text -
Choose "couriers" as the font and everything will work.
George h.
David
Thank you, i changed to Courier and the image is in order. Such a
simple circuit, I remember seeing it somewhere before, like in SAM
page.