Sheila, Ryan S, Camilla.
First we used the SEED beam to see if we were getting 00 flashes on the FCES IR camera (CLF is too dim). We did a mode scan with GR_SUS_LOCKED and a 'z step' as below on the VCO, as attached. We think that with the higher order modes a lot of the beam is clipping the edge of the FC2 AR coating and making the sizes of the peaks in the scan not representative of real powers.
z step H1:SQZ-FC_VCO_TUNEOFS '+0.01,1200' -s 0.5
Better Centering beam on FC1
We then, with the FC locked on green, used the template naoki.aritomi/Desktop/FC2_dither and adjusted the P2L and Y2L gains. With our inital sliders P2L was 8.0 and Y2L was 1.0 to minimize the injected peaks. We then stepped ZM3 in negative Pitch and then compensated with FC1 FC2 to get green FC power back up. These moves did increase power on SQZT7 IR PD from 0.3 to ~0.5. Ending sliders attached with P2L was 0.5 and Y2L was 1.5. So not completely centered, but close. O4 values were 0.8 and -1.6. See template here. We do not need to completely center green now as if we need to pico this will need to be redone.
SQZT8 Checks
Expect:
- Filter cavity FSR: 503.4kHz 66093
- Gouy phase between FC1 and FC2: 49.7 degrees, T1900649
- So, transverse mode spacing: 503.4kHz * (249.7pi/180)/(2*pi) = 503.4kHz * 49.7/180 = 139kHz. This is what we measured.
To get a IR mode scan where we can see the tops of the peaks, we turned down SEED to ~ 0.5mW, I changed line 789 in SQZ_OPO_LR.py to have a 1.2 fudge factor so that I could lock with a seed dither lock with these low powers.
Our starting scan shows a lot of mis-alignment plot and extra peaks where we think the misalignment mode beams were outside the FC2 AR coating so showing up as bright hourglass shapes across the camera. We then manually put the VCO on a 00 IR mode with H1:SQZ-FC_VCO_TUNEOFS and then maximized this with FC1 and FC2 sliders, we ended with much better alignment plot and importantly, when the SEED power was turned back up to 75mW, had our expected ~1.1mW on the SQZT7 IR diode. This is great news we have a IR beam with okay alignment/mode-matching in the FC that makes it back though the OPO to SQZT7!
I tried stepping ZM3 and then adjusting FC1 and FC2 to try to improve IR 00 mode, but the green power was getting lower which was causing frequent green lock losses so I stopped.
Next steps are to adjust FC green to be co-aligned with IR (plan to do next week) and then can continue to improve FC IR alignment to measure mode matching.
