greenie weirdness

daguin said:

Sometimes defects in the crystal or lens will cause this.

Peace,
dave

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I missed the part about this problem being intermittent. Ignore my comment. With a crystal defect, the artifact would be constant and consistent.

Peace,
dave

huh i had no idea it could be problematic at cool temps. ill have to try that out. if i could i would have had liquid nitrogen drippin on it i guess ill put a switch on the fan so if it does get to warm ill bring it back down to temp. right now i have it where my cooling fans for the various parts of my circuit cut on when i turn on the initial power.

If it were a plain LD like a red or bluray this is something that can be done.

But, when its a DPSS laser, there are a few things to consider. Cooling can lower the wavelength of the pump diode as heating can raise it.

You want as close to 808nm going into the crystals, not 807nm not 809nm. Changing the temp from the ideal which should be around 20-22C, will begin to lower your output of green as you saw when the module got warm. The wavelength of the LD begins to rise, and the efficiency of the crystals drop resulting in lower mW of 532.

Now when you cool the entire body, the crystal set also drops its temp, this is where the mode switching becomes a problem, when its too cold.

There are heaters in more elaborate systems for this reason..

Try for a decent room temperature, and you should have things back to normal. I keep my large heatsinked greenie portables in a nice warm cozy pocket in the winter months for this very reason.

DPSS has several temperature problems. Obviously there is the pump diode that you want to keep tuned for optimum absorption by the solid state laser - this is the main problem of losses in dpss systems.

But even if you sort that out (using TEC, heaters etc) there are still optima to deal wth in both the solid state laser and the doubling process. Ideally, you would need to control the temperature of 3 different parts for best results, but doing so is rarely feasible.

If the beam divergence is going up to 45 degree. i think it's the lens problem. some of my laser, they don't assemble lens very well. sometimes they will drop out from the host. Like Benm said the mode hopping can't cause the 45 degree beam divergence.

its not a total beam divergence its like what wannaburn was showing us in his video im having some computer issues but ill get my vids up i happened to catch it when it was happening.

sounds like something is loose in there and is refracting/reflecting part of the beam.

Thanks for that vid, wannaburn. Nice to have a visualization of what mode hopping looks like.