I want to measure the thermal lensing I'm introducing on a Nd:YVO4 crystal. I setup the following optical layout:

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This way the HeNe beam passes through the crystal and reflects onto a panel. I expected increased divergence with the pump on but I'm getting some really fantastic refraction I am hoping someone can explain.

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This is with the pump off. The two horizontal spots are due to the back reflection of the angled mirror. The duplicated vertical spots I think are reflections caused by the crystal not being perfectly aligned with the cavity.

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This is with the pump running in a power range where the cavity remains stable.The pattern is different -- there are more spots. But the divergence is about the same.

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But when I turn up the power past where lasing stops I get a ton of diffraction.

Is this expected? This crystal does have a fracture in it. I was hoping I could still use it to measure the lensing I'm getting.

Thanks for any ideas.