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Pinky's Brain

Sun Dec 05 2010, 09:33PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Daedronus wrote ...

The water has another important role, besides cooling, it filters most of the UV from the flash lamp.

AFAICS pure water will let pretty much all UV down to 250 nm through ... is it supposed to get saturated with ozone so it filters the UV?

Daedronus

Mon Dec 06 2010, 07:09AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

Pinky's Brain wrote ...

Daedronus wrote ...

The water has another important role, besides cooling, it filters most of the UV from the flash lamp.

AFAICS pure water will let pretty much all UV down to 250 nm through ... is it supposed to get saturated with ozone so it filters the UV?

I'm not 100% sure, I remember reading about this in the Solid State Laser Engineering book.
There was a comparison between a system using a flow tube filter (for UV and 1064nm, since 1064nm from the flash lamp will rob pump power) and one using just water, and it concluded it wasn't much of a difference in output power.

Dr. Shark

Tue Dec 07 2010, 04:46AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Marko,
I forgot 90% of what I knew about lasers, but maybe I can still help you get started. I build a YAG laser about 10 years ago and it was a huge pain in the ass. I got it lasing but had to dismantle it shortly after. Maybe I can hook you up with some parts, but it's a bit difficult since all my laser stuff is in Germany and I live in the US now.

Getting the cavity aligned is the hardest part, especially if you are cheap and making your own mirror holders. Essentially you have 4 degrees of freedom that need to be tweaked perfectly. The usual procedure is to use a HeNe laser that is bounced off of two adjustable first surface mirrors which you shine through your laser rod. You tweak the two mirrors until the multiple reflections through the rod all end up at the same spot. Then you add the first cavity mirror and repeat, but this time you do not touch the mirrors that steer the HeNe beam but just tweak the cavity mirror. Repeat with the second cavity mirror. I think Sam's laser FAQ explains this much better. In any case you will need a fairly sturdy base to bolt down all the parts + the HeNe, I used a 1cm aluminum plate to build a makeshift optical table. You can build your own mirror holders if you have access to a rudimentary machine shop, but you have to be meticulous to avoid hysteresis and slop in your adjustment or everything will go to hell if you bump the table.

Forget about the mechanical q-switch. Seriously. It's just going to make the whole adjustment procedure 100x more painful. The nicest way to q-swich would be to use a Chromium:YAG saturable absorber, but they are exceedingly difficult to find. The next best thing is to use a Pockels cell, which is a project in itself since IIRC it needs a ~20kV supply switched with a risetime in the single digit nanoseconds. Pretty much the only way to do this is with a Krytron, which are hard to get since they contain radioactive Cobalt and have export restrictions since they are used for detonators in nuclear weapons.

In a pinch, you can q-switch a laser by inserting a piece of thin carbon paper in the cavity. Amplified spontaneous emission in going to burn a hole into the paper, at which point the cavity starts resonating and you get your pulse. One of my professors told me he did this, I have never tried it and could not find literature on it.

Nd:YAG rods, cavities and flash lamps are usually easy to get on eBay, although not necessarily on a SSY-1 budget. I would not worry too much about doping concentrations and Xenon vs. Krypton. Avoid the huge glass rods, the are designed to be amplifiers and not resonators and have gain over a wide wavelength range. You can make a reflector from a polished coke can if you can't find one. Make sure the rod has AR coating in perfect condition on both ends, if not it will be completely useless. Good optics are a lot harder to find, and if you are planning to q-switch you might want to get a separate OC with a lot more transmission (say ~10% as opposed to 1%). You also may want one of those nifty IR fluorescent cards to be able to see your laser beam before it gets strong enough to burn stuff, but again they are hard to find.

I'll probably remember a lot more if you go ahead and ask detailed questions.

Zero

Sun Jan 09 2011, 07:52PM

Registered Member #3588 Joined: Sat Jan 08 2011, 11:19AM
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Posts: 36

Making such a laser yourself is very hard. The cavity is very very very hard to make...

If you wanna play with it...no serious stuff...buy a complete head.

Daedronus

Mon Jan 10 2011, 10:05PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

The alignment is hard but not that hard, if you have true gimbal mounts (they are rather cheap, about 65 + ship for 2).

Good optics are also cheap, from the Chinese sellers.
I would recommend a HR mirror that has a 2-3meters curvature. The alignment will be much easier.

The OC mirror should be around 60%(reflect) for a flash lamp laser.

Personally I don't like the ssy1, it's too small for my taste.

For me the hardest part is making the pump chamber reflector, but with access to a CNC you can probably cut the 2 sides elipsoids, out of copper, polish them, they gold coat.

A very cheap reflector that does work is the aluminum foil, I did test it, and it works, but it wasn't too good for me.

And last, why would a nd:glass rod be bad? I have a welder head that has a nd:glass rod, about 360mm length, configured as resonator.

Zero

Tue Jan 11 2011, 08:45AM

Registered Member #3588 Joined: Sat Jan 08 2011, 11:19AM
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Meant the chamber itself. Alignment is a pain as well though.
But I agree....the SSY is small. A signel-action 3J pulse-laser head would rock. Advantage: You dont have to align mirrors of the SSY ^^

Dr. ISOTOP

Wed Jan 12 2011, 04:29AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Lamp-pumped IR lasers are so much easier to make than diode-pumped greenies. Only two mirrors, no thermal issues, no messy doubler alignment.
Daedronus, where are these 2 for $65 gimbal mounts you speak of? I need some for my project.
Nd:Glass has poor thermal properties.

Daedronus

Wed Jan 12 2011, 08:22AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

Mounts:

The thermal properties of nd:glass should be the only downsize.
On a low repetition system where the temperature is not a problem, nd:glass should be better...in theory.

Zero

Thu Jan 13 2011, 08:43AM

Registered Member #3588 Joined: Sat Jan 08 2011, 11:19AM
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Posts: 36

I have CHT YAG...most efficient YAGs...I believe.
Would rock to make a mighty single pulse laser-head with one of those.
Some of them are with water-cooled cavity...20hz rep. Should be able to give some Watts.

Daedronus

Wed Feb 09 2011, 12:04AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

Speaking of CHT:YAG

I wander if this would work as a optical coupler for a CHT:YAG resonator:

,!i8E%29sJqKiN-BMkMGkUIPQ~~_12.JPG

I have no less then 3 CHT:YAG heads......that I got in order to get the nd:yag head

I think they are less efficient then nd:yag, but the output wavelength, 2100nm has some interesting aspects, because it's absorbed by water.

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