Experiment on 5/1
- CM1 right knob was moved 1div (10um) backward such that the spots were better centered on the mirrors
FM1 (A5): h=-0.2mm -> 0.4mm made the spot much darker but still it has a few scattering spots.
FM2 (A14): h=-0.8mm -> 0.2mm reduced the number of spots from 2 to 1. And it is darker. The remaining spot at the center.
CM1 (C11): h=-1.3mm -> +1.0mm made the spot much darker.
CM2 (C12): h=-0.7mm -> +0.2mm remains dark.
Note: CM1 h=1mm and CM2 h~0mm are good locations. h+ is the good direction to move. Avoid h-.
FM1 and FM2 has the scat spots at the center. Want to go h+ more.
Uniformly go h+ is the good move. => This can be done by rotate CM1 positive => CM1 right knob CCW.
Improvement of the transmission from 93.9%->95.3%
- Further moved CM1 right knob 0.5div (0.5um) backward such that the spots were moved to h+ directions.
FM1 (A5): h=0.4mm -> 1.1mm (there is only one spot rather than multiple spots)
FM2 (A14): h=0.2mm -> 1.1mm (darker but multiple spots)
CM1 (C11): h=1.0mm -> 1.8mm (brighter but single spot)
CM2 (C12): h=0.2mm -> 1.5mm (dark multiple spots)
Not much improvement of the transmission but kept 95% level.
- Replaced FM1 (A5) with A1 mirror (No photo)
Good news: This did not change the cavity alignment at all.
- Tweaked the CM1 angle
=> A1 mirror does not improve the transmission much.
Next Plan: Use A5 (or something else) as FM2 and see if A14 caused the dominant loss.