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Q-Switching via Saturable Absorber
I am trying to experiment with converting a Nd:YVO4 laser from CW to Q-switched. This is a laser I built on an optical breadboard. I'm currently running CW with about 1 watt of power emitted from an 80% reflective OC. I have Cr:YAG crystals with initial transparency of .2, .5 and .8 to experiment with.
I have inserted the Cr:YAG crystal between the HR and the Nd:YVO4 crystal. There is an additional fold mirror in between that is HR 1064 HT 808 and is used to pump the crystal via a fiber pumped diode array.
I've not gotten the laser to work with any of the crystals inserted. I have two issues I don't have a good feel for:
- I assume the Cr:YAG crystal has to be perfectly aligned. The crystal is ~ 3mm thick and anything less than perfect is going to skew the beam a little bit due to refraction. But the Nd:YVO4 crystal always refracts my alignment laser a little so for aligning in CW mode I always have to walk the end mirror a bit to get it working. I have tried that with the absorber crystal but no luck. Am I thinking about this right?
- I don't know how much, if any, additional pumping I'm going to need to get this lasing. It will definitely be a little higher because when bleached the absorber still has some loss. But I'm pumping well past threshold. I assume here that getting the crystal to bleach requires surpassing the absorber's saturation intensity?
Thanks for any ideas.
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