YVO4 Crystal 5x2.9x9.6mm Yttrium Vanadate

Laser Project said:

I can sure tell when the crystal is getting too hot, if I over drive it... The efficiency drops, I can get 550 mw out of it at 3.7 amps of current to the IR diode, push that up to 5 amps and the output drops to 400mw and lower. If I had a TEC controling the crystal temperature, I could probably get 800mw out of this thing.

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Yes--perfect alignment, fine tuning and stablization of temp is an art that requires hands on knowledge and experience over time. It has been found that thermally induced phase mismatches reduce the conversion efficiency, but can be partially compensated with intentional mismatches introduced by means of a small rotation of the crystal away form the nominal phase matching direction.

Be careful you dont ruin the KTP--can easliy happen. With the correct crystals and a perfectly on target frequency 808nm pump you should have no trouble getting 1W to 1.5 W of 532nm

In very high output powers, the KTP crystal becomes susceptible to actual optical damage. Thus, high-power DPSSLs generally have a larger beam diameter, as the 1064 nm laser is expanded before it reaches the KTP crystal, reducing the irradiance from the infrared light. In order to maintain a lower beam diameter, a crystal with a higher damage threshold, such as LBO, is used instead.

Whatever you do be ultra careful of safety especialy of your eyes, is needless to say but can't be said enough.

when the KTP is burned, does it normally quit working or have reduced output? So far, I haven't harmed it that I know of. If the output dims, I back off on the voltage to reduce the drive current.

Laser Project said:

when the KTP is burned, does it normally quit working or have reduced output? So far, I haven't harmed it that I know of. If the output dims, I back off on the voltage to reduce the drive current.

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Sounds like it is OK--you can physically inspect for optical damage--flux-grown KTP crystals suffer from blackening and efficiency breakdown ("grey-track") when used during second harmonic generation process of 1064nm at high average power levels to create 532. Second harmonic generation is and interesting thing used in many ways.
Second harmonic generation is a nonlinear optical process, in which photons with the same frequency interacting with a nonlinear material are effectively "combined" to generate new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons.

Grey-track gives rise to harmonic power instability (for many intra cavity doubling cw laser), efficiency drop and crystal blackening (for high power-high repetition rate laser) and sometimes the process is accompanied by beam distortion (when the beam is strongly focused within the crystal).

Keep in mind that both 808nm and 1064nm invisible and do not trigger the defensive "blink-reflex" reaction in the eye and can therefore be a special hazard to the human eyes----low cost pointers don't usually have IR filters and llaser safety eyewear intended for argon or other green lasers may filter out the green component (giving a false sense of safety), but transmit the infrared.

Great help in understanding this technology, thank you. I am using a FAC 4 watt 808nm C-Mount diode in this laser which was supposed to put out a square 8 X 8 deg. raw beam but I think I was sold the 8 x 30 degree FAC'd diode instead because the output is a thin line of green. I peaked the output of the crystal by rotating the diode and at peak power, instead of a dot, I have this rectangle. I tried to get TEM00 but when I get a spot which looks like that, the power output is much lower. Any suggestions? Maybe I can't get TEM00 with this particular diode, I don't know. If this means much in regard to knowing if the diode is multimode or not, it was specified for 200 um.

Rotating the laser diode for max output and with the beam expander on it, the optics makes the rectangle appear to be a dot on the wall, but when I go outside and use the laser at night, I can see the beam is still the same. The divergence isn't bad with the 8X expander I have on it now, but when I rotate the laser in the night sky, I can see the beam is thin on one side, and several times wider on the other with a ratio which corresponds to the 8*30 degree raw output, but only in ratio because the beam doesn't spread from divergence (that I can see). I didn't notice this until tonight.

IR does concern me, worries me, so I'm being careful about that.

Laser Project said:

Great help in understanding this technology, thank you. I am using a FAC 4 watt 808nm C-Mount diode in this laser which was supposed to put out a square 8 X 8 deg. raw beam but I think I was sold the 8 x 30 degree FAC'd diode instead because the output is a thin line of green. I peaked the output of the crystal by rotating the diode and at peak power, instead of a dot, I have this rectangle. I tried to get TEM00 but when I get a spot which looks like that, the power output is much lower. Any suggestions? Maybe I can't get TEM00 with this particular diode, I don't know. If this means much in regard to knowing if the diode is multimode or not, it was specified for 200 um.

IR does concern me, worries me, so I'm being careful about that.

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Would guess you are overdriving the crystal system designed for a 250mw laser quite a bit with a 4W 808 nm pump.

The 200um would mean 200um X 1um emitting area. FAC collimation lens effect comes in3 options---Square Beam End/Strip Beam End/Line Beam End.

The two main causes of mode-hopping are temperature and unstable power sources. To make sure that the dominant mode is TEM00, or the clean beam the internal parts of the laser need to be precisely aligned and properly temperature regulated.
TEM00 is the weakest powered mode there is. Generally speaking, the more separate blobs of light there is in your beam, the more of the laser cavity your laser is making use of, which generally means increased power output.

Glad you are being careful about the IR---is a dangeruous 4W relatively high output laser if eyes are not protected.

I'm afraid to even look at the dull red spot from a IR diode against something, fearing the reflection, even if a matte surface. OK, that explains the power increase, thank you again. I am so happy someone who knows this stuff will answer my questions.

Laser Project said:

I'm afraid to even look at the dull red spot from a IR diode against something, fearing the reflection, even if a matte surface. OK, that explains the power increase, thank you again. I am so happy someone who knows this stuff will answer my questions.

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Maybe this site would be of interest to you. A lot of practical DPSSL 532nm information

Sam's Laser FAQ - Home-Built Diode Pumped Solid State (DPSS) Laser

Thank you, I've read some of Sam's stuff, but didn't know he had a section devoted to DPSS. I've been reading it, saved it to a Word doc for further reading.

great info in this thread here Encap, I tried to rep you yet it says I already have, I dont recall where! Thanks + Thanks to LaserFAQ also.