Attached a transfer function from yesterday and today along with the pump laser output.
Basically when we had >840mW, something was noisy and EOM couldn't handle it.
Now that we're down to 770-780mW the loop behaves okay again.
This is the laser output and green production out of the SHG (1day)
SHG scan looked fine. There was no obvious multimode or misalignment yesterday.
We had >840mW yesterday with less green production out of the SHG compared to today. Funny.
The transmission of green from the coupler to SQZT6 also has dropped to 20%. I was able to recover some yesterday with the two pick-off mirrors before the coupler but once the power started to fluctuate it's difficult to do any optimization. I'm still hopeful that this is an alignment drift issue. Would be nice to install additional picomotors there.
Note that the current temperature readout off the controller box is 29.71 C, current is 2.116A. This number has drifted since Haocun and Sheila adjusted the knob last week (alog45604, the 25 was probably 29 but I believe the decimal point to be accurate).
Turned out the pump laser monitor PD sees the back reflected beam from SHG. So the plot above makes sense. When amount of green power and red trans goes up, back reflected red goes down. I found that the faraday holes were never opened to let rejected light out. I also installed extra beam dump to dump the beam that shoots upward. Both beam (see attachments) shows in the photos belong to back reflection. Opening the holes seems to help with the back reflected problem that leaks into the monitor PD (though it doesn't solve the problem, hopefully it makes diagnosing issue less confusing).
I installed another Thorlabs PD to look at the Mephisto (pump) reflected beam off the first QW. This is as close to the Mephisto as I could get before it hits the faraday. The output is plugged into the extra AI channel 3 on the SQZ rack. This is just in case the monitor PD is still contaminated with the SHG back reflection (I think it still is). And might help with the diagnostic if faraday is the problem. Hopefully not...
