This is a legacy single oscillator cell Nd:YAG laser. All electronics seem to be in quite good operational shape. All optical components present do not show any obvious damage. There is an optical schematic on the internet:
We don't have the spatial filter components only. We aligned using HeNe lasers; the HeNe goes in and out on the center axis of the YAG rod. After alignment, we can get quite robust free lasing, ~150 mJ per shot. The problems come with Q switching. The Pockels cell was aligned with the HeNe to give a cross image through crossed polarizers; the Q switch timing was initially set to what should be set to a near optimum time based on observing the flash output with a photodiode. Q switched output does take place. However, instead of an expected circular burn, the burns are narrow vertical ellipses. It is the kind of burn pattern you might perhaps expect if the YAG rod had a horizontal rotation--yet the HeNe alignment, and good free lasing, do not seem to be consistent with that.
So, what's going on? Without the spatial filter there may be less mode specificity, but I don't see how that could cause something this extreme. What (silly) things are we doing or overlooking?
New Orleans, LA USA
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