Nd YAG laser 1064nm spot question

Hello all. Im new to this forum so im not sure this is the correct place to ask this but here goes. I purchased a laser welder for a project. Im currently performance testing it and have hit a roadblock. The beam size for this laser is 6mm in diameter. The laser is rated for 0 to 3000W up to 20ms pulse time. The problem im having is the spot shape goes out of round after a few minutes of welding. Ive monitored the temp of the cooling water and the cavity and am well below the upper operating limit of 35°C at 24°C max. When the beam gets deformed it forms a circle but the top and bottom appear cut off. The shots are taken after the OC lense and before the beam expander lense at 1500W 5ms. If i dont adjust anything and let it sit overnight the unit works fine again the next day for about the same amount of time/work then i lose power again and when i check the beam cross section its deformed again. Ive done a number of different tests to try to eliminate possible culprits. The only thing left that makes sense is that somehow the Nd YAG crystal is warping due to lensing effect or the flash pump needs to be changed or the cavity is warping. The cavity is a ceramic cavity inside a plastic (teflon?) block. Any help or suggestions are appreciated.

I've never worked with Nd YAG but once and a while on my old co2 5kw, a mirror or lens would get contaminant on it and as the laser was used, thermal stresses would warp the beam shape. After cool down, would work fine but heat again would cause issues. Took a while sometimes to track down exactly what component was the cause.
You may want to ask over on laser pointer forums. Those guys have tons of troubleshooting exp.

FRITZHID said:

I've never worked with Nd YAG but once and a while on my old co2 5kw, a mirror or lens would get contaminant on it and as the laser was used, thermal stresses would warp the beam shape. After cool down, would work fine but heat again would cause issues. Took a while sometimes to track down exactly what component was the cause.
You may want to ask over on laser pointer forums. Those guys have tons of troubleshooting exp.

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Hello Fritzhid. Thanks for the response. Thermal distortion due to contaminated lenses was one of the first things i had thought of too. So all the lenses throughout the machine have been cleaned with a lense cleaning solution or acetone using the dropper on lense cleaning tissue method where you wet a tissue with acetone and drag the tissue across the lense. But i am leaning in this direction in wondering about the Nd YAG crystal itself heating up and distorting.

That is a distinct possibility! Any thermal variation in the crystal would cause distortion, especially if the partial mirror is misaligned from the beam path.
A defect (any numerous causes) in the crystal would cause this.
Beam alignment is critical in these laser processors. Many newer co2 machines employ an active beam adjustment mirror to compensate for this but Idk about pulsed laser systems.