Frankenstien 300mW DPSS Video

[300EVIL]

Hey Guys,
This is my 300mW DPSS laser I assembled from parts. It's a small 2X2X4mm hybrid KTP/YVO4 pumped by a 2W diode through a grin lens. It seems to put out quite a bit of power for a while but it fluctuates like hell! Here, check out the video. http://www.youtube.com/watch?v=LPJvtCY4CEQ
As you can see the driver stays steady but the power output just jumps around like crazy. I've had it hit as high as 380mW and as low as 200mW all while the diode is getting a steady diet of just under 2.8A. My guess is that temperature fluctuations in the crystal is what's causing these big jumps. With the lights turned off, you can actually see the output get instantly dim for a few seconds then instantly bright again. It also spikes bright/dim sometimes but never goes above the set current on the driver. If anyone could shed some light on how I should go about fixing this problem, that would be greatly appreciated.
Thanks!
Adam

[dave]

I dont suppose that brass barrel is one of these?

http://cgi.ebay.com.au/LASER-ND-YVO4...QQcmdZViewItem


To increase the stability, you will need to keep the 808 diode and crystals at a constant temp via a tec..

Is that 300mw including IR?

[dave]

Just did a bit of snooping, and i see you have bought one off this guy.

That started its life as one of these:

http://cgi.ebay.com.au/ws/eBayISAPI....3557&rd=1&rd=1


These don't have any IR filtering in them so the 300mw is proibably an exagerated measurment. If your driving them harder with a new diode, i question how long the crystals will last.

[300EVIL]

Hi Dave,
Yes that's the one. I thought I saw an IR filter under the collimating optic but it now appears it's just the AR coating on the crystal. I put an IR filter from a laser pointer in front of the beam this morning. Now I'm looking at 270-160mW,, Not literally! You get the point.... So yeah, not exactly 300mW but close. According to the guys auction I should be able to drive the laser at the full 2W of pump energy. The diode is just running at operating current which is 2.8A. Do you think 2W is too much for that size crystal? He's saying you can throw up to 5W at it, that I find hard to believe.

[eyceage]

I've seen quite a few auctions from "aerodynamics2006", and while his stuff is a bit better nowadays I would not trust anything he says.

In one case he was buying $25 wedge prisims and selling them as Vanadate/KTP combos for a few hundred bucks.

I also saw him win a nice omnichrome for around $750, then list it a couple of days later for around $1500.



TEC with feedback sounds like what you need to stabilize your laser. At least you can get some green out of it!

[mixedgas]

the diode is getting a steady diet of just under 2.8A. My guess is that temperature fluctuations in the crystal is what's causing these big jumps. With the lights turned off, you can actually see the output get instantly dim for a few seconds then instantly bright again. It also spikes bright/dim sometimes but never goes above the set current on the driver. If anyone could shed some light on how I should go about fixing this problem, that would be greatly appreciated.
Thanks!
Adam[/QUOTE]

one, get rid of the brass, its a lousy heat conductor , go to a aluminum tube, second you need a lot more heatsink and heatsink compound for a passively stabilized laser. Make friends with a machinist, what you need is not hard for anybody with a decent shop to make, it will take more time to make the drawings then the partz. Are you using a yag/ktp bonded crystal?

quick test, get a can of "component cooler" spray, turn the diode current down to about half and slowly cool the diode end of the laser with the spray (dont get it on bare optics/ktp) you should see it slowly get more green then peak then decline, measure the peak with a thermocouple or other very small temperature sensor, thats about where you want your tec to cool to.
I used to use this method to optimize green pointers, so I could back off the diode current.

Steve Roberts

Steve Roberts

[stanwax]

evil
how big is the hybrid xtal ie length width depth. If its only a little one as some of these pointer ones are I doubt you would have any trouble killing it with 5W of pump power. You may get away wit 2W but it depends on how well you can couple some cooling to it. The diode will need to be cooled and pref. temp stabilised at whatever temp maximises its useful output. What I mean is if its bang on 808 at room temp then you need to keep it at that temp. too much cooling and you could lower the wavelength so its not providing pump energy at a wavlength that the vandate will readily absorb = poor effeciency. The hybrid xtal is always a compromise as the vandate and ktp will optimise at different temperatures - which is hard to achieve when they are bonded together. However your problem is getting the heat out of them and maintaining some level of control to keep them at their optimum thus giving you a stable output. Just cooling the brass barrel will help but if there is not good thermal conductivity between the xtal and the brass you are still gonna fry it up. How warm does the brass bit get when you are running it? If you can feel heat then maybe there is half decent conductivity between the xtal and the brass housing - which is good.
So ideally you want heatsinking with temperature control using Tec's but just to get you going a bit some cooling would be better than none.

Rob

[eyceage]

This was the item I was referring to:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=260143732555

aerodynamics2006 was reselling them for $300 as KTP/vanadate combos, which of course, they are not.