Anyone know anything about frequency doubling lasers

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Anyone know anything about frequency doubling lasers

Postby Jerry » Wed Sep 21, 2011 6:22 pm

I have a few laser diodes, 32 watt and 40 watt 808nm Coherent FAP (Fiber Coupled) laser diode modules. The IR wavelength is pretty useless in itself due to its shorter wavelength. But perfect for pumping solid state lasers.

Over on electronic goldmine's site they have some YAG rods and KDP crystals for very good prices:

http://www.goldmine-elec-products.com/p ... ber=G18404
http://www.goldmine-elec-products.com/p ... ber=G18405

The rod appears to be pretty pale which suggests it was made for CW operation. I am thinking 808nm to the rod to pump it, 1064nm comes out and into the KDP where it is doubled to 532. The KDP is where things get a little into the unknown for me. I know KDP is also use for Q-Switching, so is there different crystal structure between a KDP for SHG and Q-Switching?
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Re: Anyone know anything about frequency doubling lasers

Postby Joe Jarski » Wed Sep 21, 2011 7:39 pm

This is how things work based on my knowledge...

The YAG rods aren't mirrored on the ends like some others are, so the mirrors are a separate external item. They're aren't always flat either - some are convex. The Q-switch, if you're using it, sits between the YAG rod and the fully reflective mirror. The KDP crystal is external to the LASER cavity, so it sits out front of the partially reflective mirror. The Q-switch on my 110W YAG looks to be a galvo setup to interrupt the beam in the cavity between the rod and the fully reflective mirror. I haven't heard about using a KDP crystal for Q-switching, so I'm not to sure about how that would work.

YAG rods tend to look different in photos as compared to seeing them in person. It depends on the lighting also, but I wouldn't put too much stock in what you see in the picture to identify whether it's CW or pulsed.
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Re: Anyone know anything about frequency doubling lasers

Postby Jerry » Wed Sep 21, 2011 9:23 pm

You mostly have it. There is a basic design here:

Image

Here is a data sheet on the KDP crystals. They can be used electrooptically as well as a SHG.

I just don't know if there is any difference.

-Jerry
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Re: Anyone know anything about frequency doubling lasers

Postby Doug Coulter » Thu Sep 22, 2011 10:16 am

I don't know much, but those prices look nice enough to take a chance on and see. I found this on wiki: http://en.wikipedia.org/wiki/Nonlinear_optics which seems to say that xtal orientation is important for frequency doubling, but also says KDP is what's used to double YAG, not KTP as shown in the laser pointer diagram (which actually makes sense). The one laser pointer I took apart does look like #2 in your diagram. Their KDP xtal looks longer than what you'd use for frequency doubling, but ???

I have a really big ND:YAG laser that's deep purple rod, though you can get a red laser pointer beam through it. Looks like mine has either no mirrors or they were external. Huge krypton flash tubes (obviously this was meant for pulses). The guy I got it from (Frank Sanns) says it will punch though quarters when pulsed -- the caps and inductor are huge (1500 joules for 60j output).
I haven't had the guts to fire it up yet, not knowing what end any beam might come out of -- Frank said it works as is, however. I'd think it wants to be Q switched to get all the output into one pulse instead of a burst of them. There's some info here: http://en.wikipedia.org/wiki/Nd:YAG_laser which interestingly says that the Nd:YVO4 might actually be a little ND laser in those laser pointers.

I know the YAG wavelength is one of the more dangerous to humans - a heck of a lot of "black" stuff is transparent to near-IR, which I've found out the hard way making reflective object detectors in that range, and it's close enough for your eye lens to image on the retina, so it's something to be really careful with at "power". If I were going to mess with it, I'd have some safety glasses (not that there's anything that will hold off watts -- but better than nothing) and some real good purpose-designed beam stops before I got in the room with that.

I once worked with a 10w green laser, argon, CW. That thing was a beast, a lot of fun (since I didn't own it and someone else fixed and fed it). Easy to make holes in things with.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Anyone know anything about frequency doubling lasers

Postby Jerry » Thu Sep 22, 2011 5:18 pm

Vandanate crystals (Nd:YVO4) are usually used with DPSS lasers since they absorb the 808nm better than the generic ND:YAG. KTP is also used for 1064 freq doublers. Probably more common now than KDP.

One interesting about YAG crystals vs ruby is they dont selfabsorb their emitting wavelength. WIth a ruby laser you have to make sure you excite the whole rod or it will absorb a lot of the beam energy.

This looks interesting:

http://www.ebay.com/itm/ND-YAG-and-LBO- ... 1c1af46c93

Full set of crystals that will output blue. Sent a question to find out max input power.
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Re: Anyone know anything about frequency doubling lasers

Postby Doug Coulter » Fri Sep 23, 2011 8:55 am

Yes, I suppose new materials come along and work better. Seems very doubtful the word "laser" really applies to any of this re coherence. I don't see the optical resonator over the primary media for one thing. Just looks like fluorescence, not lasing, at least to my old eyes. Not that it matters for most applications. And getting to that, what did you have in mind for this, do you hae something specific, or just some fun in the lab?

I'd love to come up with something short enough wavelength to work with dichromate resist and be able to direct-plot on it (it's fairly numb stuff - takes a couple minutes of sun). That would be blue/uv I suspect to get it done in any reasonable time. Either that, or get my hands on some other resist that would work for various photo-chemical things. The big advantage of the dichromate/PVA stuff is I can make it myself - the popular (so I hear) Kodak stuff seems only available in quantities well past what are reasonable for a home shop. No way I can use a drum's worth before it degrades or gets exposed due to an accident getting some out of the drum.

Of course, any laser hot enough to be a weapon itself would be nice on my concealed-carry .38....no need to shoot if that makes 'em run ;)
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Anyone know anything about frequency doubling lasers

Postby Jerry » Fri Sep 23, 2011 9:25 pm

The final optic is a partial reflector. The set I posted is limited to 3 watts input. I dont think the laser diodes I have will even run that low. This is mostly just to have something to do with these laser modules.

This is not fluorescence, it is doubling the frequency. Look up Non Linear Optics.

The lasers in blue ray writers will get you down into the blue/purple range. And they are freeking powerful. I think some come in close to a watt.

Basically, you want to do stereolithography, there is a guy who came up with a process to do this using a digital projector as the exposing source:

http://hackaday.com/2011/04/01/3d-print ... provement/
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Re: Anyone know anything about frequency doubling lasers

Postby Doug Coulter » Sat Sep 24, 2011 3:54 pm

No, I wasn't saying the KTP was fluorescing, and I posted the nonlinear optics link myself, above. I'm saying that the Nd:YVO4 layer is fluorescing (808 in, 1064 out), not lasing -- there's no cavity mirrors shown in your figure so unless it's a super-radiant laser, it's not a laser. Doesn't matter here, as no one is caring about coherence. Wonder when blu ray players will be cheap enough to buy one to steal the laser out of...

I have a good number of uses for photolith that have nothing to do with circuit boards. How about selective etching of a picture of your bird dog on your shotgun, made to look like hand engraving? Huge market for things like that around here at "name your price" levels. Also, tiny, delicate, fusor parts. Not only that -- the dichromate/pva stuff is linear with exposure, so you can apply china paint with it, and bake it on variable thickness for art...I have an old friend who wants to do that. Might be able to handle curved substrates better with a computer XY controlled beam than with regular optics.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Anyone know anything about frequency doubling lasers

Postby Jerry » Mon Sep 26, 2011 9:51 pm

Look at the diagrams a little more closely, you will notice it says HR 1064 on one end of the nd:YVO4 crystal and again on the end of the KTP or the output mirror. HR means high reflectance and is basically a mirror to that wavelength. So the first mirror on the vandanate crystal passes 808nm and reflects 1064. The crystal is excited by the 808nm and lases with a cavity consisting of that mirror and either a coated end on the ktp or a separate mirror past the ktp. The final mirror passes only 532 and fully reflects 1064 so the emission from the vandanate crystal is continuously recirculated until it is doubled by the KTP. You can also have the SHG crystal outside the primary cavity as well.

Nd doped crystals have absorb the most at 808nm it happens that krypton puts out a nice spike about here and is why they are used to pump older yag lasers. 808nm diodes fit perfectly and are heck of a lot more efficient than a big old krypton arc lamp that runs at 200v, needs a HV kick to light it and needs to live in flowing deionized water.
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Re: Anyone know anything about frequency doubling lasers

Postby Doug Coulter » Tue Sep 27, 2011 1:46 pm

Ah, ok. Real short path through the gain medium, but obviously these things work. Your last paragraph pretty well describes the big Nd:YAG laser I've got here. Rod about a foot long, rectangular, about 3/32 by 1/2 inch, and a big photoflash tube in water (assumed krypton). It's rated at 1500 joules in for about 60 out. The cap is a knee high thing at 4kv, in series with a huge inductor (about 80 pounds of #2 wire). Someday I'll fire it up, no need for it now.
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