Interesting findings

I spent a little bit of time messing with this:

  1. I reworked my Matlab code to handle both X and Y dimensions of the beam so it now works with astigmatism.
  2. I tweaked the cavity design. Instead of aiming for a cavity that is stable with no lensing, this cavity is not stable until it reaches 1m of thermal lensing. This is way before threshold, so it really doesn't impact operation, but it allows the cavity beam parameters to remain more "sane" as lensing increases.

When I first built this cavity it didn't work terribly well: it would get to a couple of watts but would start to fade off like the other designs. While adjusting the pump overlap I realized that at low lensing levels there is really an enormous waist in the cavity mode; much larger than my pump mode (this waist constricts with lensing and by the time there is appreciable lensing the cavity mode waist is smaller than the pump waist). I turned up the pump power and re-aligned the pump mode to the cavity mode and...ok, this worked pretty well. I didn't drive the cavity harder than 35 amps (I've had the misfortune of blowing these second hand FAPs and that usually takes out the fiber too, so I'm a bit wary of pushing them).

Pretty graph:

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It is still mode hopping at higher powers and the dotted line shows that the laser is unable to maintain the peak power as the pump power increases. I need to figure that out -- I did notice that at about 35 amps it mode hops to a much higher mode. That may be killing it. I bought an adjustable iris I'm going to try to use as a spacial filter in the resonator, but I'm waiting on a precision x-y positioner that's back ordered.

But I am beyond excited that my Matlab code is finally matching what I measure. At least for the peak powers.