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Little help to understand SHG

diachi

diachi

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Alaskan said:
I liked this article:

http://photos.imageevent.com/qdf_fi...vecommunications/irledandlaserproject/nlo.pdf

I'm searching for information regarding what happens if you use 810nm, or to throw a number out there, 815nm instead of 808nm, how far from 808nm can the pump be off wavelength/frequency into the vanadate and then KTP before the 532nm output either doesn't work, or begins to drop off by 10 percent? Which crystal suffers the worse conversion efficiency when off freq, the YVO4 vanadate or the KTP, or do they both have similar off-wavelength inefficiencies?

Maybe I'm looking at this wrong, for example, if you shoot 1070nm into a LBO or KTP crystal you just end up with half the wavelength out or 535nm? Are all "532nm" DPSS laser pointers really 532nm?
Click to expand...

From the Laser FAQ:

The absorption curve of Nd:YVO4 (vanadate) is quite broad compared to Nd:YAG (YAG). The following is from a graph in "Solid State Laser Engineering" by Koechner. (This actually deals with output power, not absorption, but since that is the desired effect, the numbers should be similar):
Nd:YVO4: Between 806 nm and beyond 813 nm, the output power is approximately constant. The corresponds to a temperature range of 20 °C for the pump diode. The output drops to 50 percent at about 801 nm. (The graph doesn't go higher than 813 nm.)
Nd:YAG: The peak is between 809 and 810 nm with the output power down by 40 percent at 807 and 810 nm.

For pumping with diodes, the wider wavelength range of vanadate is very significant because temperature tuning is a lot less critical and for low power DPSS lasers such as green laser pointers, thermal management isn't essential (though some variation may still be evident).
Click to expand...

I was just going to say "Vanadate has a wider absorption band than YAG" but thought some numbers would be nice, so dug that out!

Edit: Just realized you were asking about Vanadate vs KTP - the thing there is that the Vanadate will always output at 1064nm (assuming you're using optics for 1064nm) so that will not be an issue for the KTP. The issue comes from the diode's wavelength shifting and then causing the output from your Vanadate to drop due to reduced adsorption. Temperature is the biggest concern for KTP, even if the temperature is a degree or two out you can see a large drop in efficiency. You can also run into thermal lensing in your Vanadate and possibly to some extent in the KTP which causes overall efficiency issues in many designs. That can also cause a reduction in beam quality.

Yes, all of the 532nm lasers are 532nm within a very small margin.
 
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Alaskan

Alaskan

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Thank you, I've been reading a few parts of Sam's Laser FAQ and must have overlooked that, did a google search and my search terms must have been bad not to pick up on finding the FAQ... excuses, excuses.. Anyway, that mystery is solved, I've been wondering on the question for awhile but keep forgetting to ask anyone, so today I tailed the question on to this thread. I have some Vanadate, a nice piece 10mm X 10mm X 1mm someone gave me as a gift and a KTP crystal wrapped in gold leaf I bought from someone but before I start doing anything with it, needed to know how temperature affected the materials.
 
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