Violet laser diode pumped dye laser

[kc2...@aol.com]

I'm going to try to pump a dye laser with a 150mw violet diode laser.
I was wondering since I have no experience with TTL modulation is the
rise time time and pulse lenth sufficient to lase before triplet
production quenches lasing in the dye? Second step may be to go with
just beam chopping. I was hoping to avoid the use of expensive EO
modulators and such.

Thanx, Keith

[STEVE ROBERTS]

You may get a IR dye to threshold at 150 mW, but visible ?????

Try for 7 to 10 nanoseconds

Steve

[kc2...@aol.com]

>
> You may get a IR dye to threshold at 150 mW, but visible ?????
>
> Try for 7 to 10 nanoseconds
>
> Steve

Why not. The average power of a nitrogen 337nm laser is 30-60mw and
that can pump blue dye. Ive seen argon at 415nm at less than 500mw
pump green and yellow dye. I know it can work, its the pulse method of
TTL for the diode I was wondering about. Thanx for the advice.

Keith

[James Sweet]

Is it the average power that matters though? I was under the impression
that peak power of a nitrogen laser is very high, not saying this can't
be done, just a consideration. By all means give it a go and report back
with the results.

[Lostgallifreyan]

James Sweet <james...@trashmail.net> wrote in
news:ge8kp8$g4h$2...@news.albasani.net:

I also read that N2 lasers had very short pulses, so high peaks. I don't know
how fast the rise time is for a violet diode but I think that like other
diodes it might be very fast. I think the diode might not be the limiting
thing but the drive, as keith suggests, but does it have to be TTL? That's
just a signalling method anyway. But soem variants are designed for extremely
high speed, so why not just parallel some logic gates from fast HCT types or
whatever does better these days. You'll need to limit capacitance on the
output by careful PCB layout. Simple resistance for current limit. As the
output gates do the real driving, the control logic can be low current so it
should be possible to devise a simple monostable and drive it at whatever
speed you like. If Phil Hobbs is around, he's maybe the best person to ask
for advice for specifics for this, as far as I know.

*cue Hobbs-shaped rabbit out of hat*

Re the diode itself, I've seen that a violet diode is far more forgiving of
excesses, so you might get by with some serious overdrive, given the
shortness of the pulse. Cheap enough to try anyway.

[Phil Hobbs]

I'm nowhere near good looking enough to be a Gallifreyan sidekick. Also the
wrong gender. ;)

N2 lasers produce ~10 ns pulses regardless of how you pump them, due to a
bottleneck in the rate equations for that system. You can't make a CW N2
laser. Driving short pulses into low impedances is a bit of a job. One good
method is to charge up a piece of coax and dump it into the diode with a
giant MOSFET. You have to really goose the FET to get it to switch fast
enough, but when you do, you get a nice flat-topped current waveform with a
clean turn-off. Inductance is the killer there--you don't use pigtails on
the coax, for a start.

For higher duty cycles, I like to put an RF transistor in parallel with the
diode, drive them with DC, and do shunt switching. A choke in series with
the DC current drive ensures that the transistor and LD current waveforms are
the same. You have to watch out for oscillations with that trick--it's
easily possible to get gigahertz ringing on the edges.

> Re the diode itself, I've seen that a violet diode is far more forgiving of
> excesses, so you might get by with some serious overdrive, given the
> shortness of the pulse. Cheap enough to try anyway.

Whether it's peak or average power that matters depends on the lifetime of
the upper state you're pumping. For instance, you can get high peak power
out of a Nd:YAG pumped with a 100-microsecond flash lamp, because the upper
state of Nd^(+3) is about 250 microseconds iirc. Dyes have much much shorter
upper state lifetime, about 5 ns for Rhodamine 6G in ethanol, so you're
integrating the input pulse over a much shorter time. You have to pump it to
threshold in a few nanoseconds.

There used to be a fair number of CW dye lasers around, but you have to pump
a small volume extremely hard to do it.

I've never used a violet diode, so I can't comment on their overdrive resistance.

Cheers,

Phil Hobbs

[Lostgallifreyan]

Phil Hobbs <pcdhSpamM...@electrooptical.com> wrote in
news:JKSdnScAta3aLpXU...@supernews.com:

> I'm nowhere near good looking enough to be a Gallifreyan sidekick. Also
> the wrong gender. ;)
>

Never mind sidekick, if you can post like that you can drive.

[Samuel M. Goldwasser]

Lostgallifreyan <no-...@nowhere.net> writes:

Even a simple home-built N2 laser will have ns risetimes and kWs to 100s of
kW or more peak power. It's the latter that may end up being the issue.

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[Samuel M. Goldwasser]

Phil Hobbs <pcdhSpamM...@electrooptical.com> writes:

Not much. :)

[STEVE ROBERTS]

I own dye lasers, yes, I've seen 500 mW threshold a flowing jet from a
lexel 88 no less, But your not going to get that kind of pulsed peak
power from the violet diode.
Even if you can find a way of pulsing it, your going to run the risks
of blowing the diode faces from the high intracavity power density,
good luck, but until a 1-2 watt cw violet comes up, I doubt it. Or
just modify a cr series dye for 3 or 4 pumps from cw violet diodes. I
dont know if you can get the spots colinear in the dye jet.
You might combine two of them with polarization. But there is a
difference between threshold and useful power.

you need a avalanche transistor switch. I have posted links to those
before. I just wonder if you can get them down to 20-30V and a short
enough pulse to do it. Got a really fast o'scope before you try this?
Steve

[Alexey Galakhov]

On Thursday, October 30, 2008 1:02:29 AM UTC+5, Phil Hobbs wrote:

> There used to be a fair number of CW dye lasers around, but you have to pump
> a small volume extremely hard to do it.

How about pumping a CW laser with a bunch of 445nm laser diodes? They are about 1W each. Considering just one 1W diode, how small should the volume be to achieve the threshold?

[Phil Hobbs]

You have to hit the pump bands of the dye, and the dye has to be flowing
in a very stable stream. The dye stream itself is part of the laser
resonator, of course, and forms a nasty toric lens--short focal length,
nearly but not quite cylindrical--so the cavity design is an
entertaining optical problem.

Dye is quite unstable as well--you only get about 10**6 fluorescent
photons from a molecule before it dies from some low-probability
electron transfer reaction. Thus you have to keep it moving, and change
it often. Rhodamine dyes are fairly poisonous, and are often mixed with
dimethyl sulfoxide (DMSO). DMSO is a skin transfer agent--it causes
whatever else is on your skin to pass through, which obviously makes the
dye much more dangerous. (If you have DMSO on your hands and pick up a
banana peel, you'll taste bananas, or so I'm told.)

I've never built a dye laser, but you could look in the late great Tony
Siegman's lasers book.

BTW Tony used to be a regular poster on sci.optics (as AES) until he
died in late 2011. I took his lasers class about 25 years ago, and he
narrowly escaped being on my dissertation committee (I was defending in
the summer, and he wanted to spend the summer doing research and not
reading people's theses. I was disappointed but not upset, because he
really was one of the white hats.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[Alexey Galakhov]

> You have to hit the pump bands of the dye, and the dye has to be flowing
> in a very stable stream. The dye stream itself is part of the laser
> resonator, of course, and forms a nasty toric lens--short focal length,
> nearly but not quite cylindrical--so the cavity design is an
> entertaining optical problem.

Yes. There is a Russian CW dye laser "Ametist" that has 4W Ar pump and is capable of producing 100mw tunable output. I guess one can borrow the design more or less. It is mostly published.

> Rhodamine dyes are fairly poisonous, and are often mixed with
> dimethyl sulfoxide (DMSO). DMSO is a skin transfer agent--it causes
> whatever else is on your skin to pass through, which obviously makes the
> dye much more dangerous. (If you have DMSO on your hands and pick up a
> banana peel, you'll taste bananas, or so I'm told.)

Oh thanks, I know the properties of DMSO (and I don't like them). AFAIK Rhodamine 6G may be used in alcohol solutions too. It's MSDS says that it is 2-1-0 and LD50 400mg/kg (rats) so it is safe enough to work with with usual precautions. Not a potassium cyanide :) I worked with a laser-pumped R6G laser before.

> I've never built a dye laser, but you could look in the late great Tony
> Siegman's lasers book.

Good point. I actually wanted to buy this book some time ago. I used to read "Principles of lasers" by Oratio Svelto for the theory but I don't quite understand the CW dye physics from that description.

Regards,
--
Alex