PeterK and RickS
- FSS AOM replaced. Heat sink, aluminum baseplate, kapton insulators, nylon screws added. (see photo below)
- Measured RF power at input to AOM: 22.5 Vp-p -> 7.96 Vrms -> 1.27 W. About right.
- Aligned AOM. Power just upstream of AOM: 68 mW; Power just downstream: 58 mW. 85% efficiency. Very good.
- Second pass, measured just upstream of EOM: 47 mW; 81% efficiency. Good. Double-pass efficiency 69%. Good.
- Power downstream of EOM, downstream of RC modematching lens L12: 47 mW. Good.
- M27, first turning mirror downstream of EOM was not locked, now is.
- Aligned into reference cavity using two periscope mirrors. Max Tx PD DC out: 2.37 V. Locked both periscope mirror mounts. TxPD DCout after locking mounts: 2.35 V.
- Centered beam on RFPD. Locked all three actuators on first steering mirror upstream of RFPD.
- FSS RFPD unlocked: 360 mW; locked: 37 mV -> 90% visibility. Not too bad.
- TTFSS gains (FAST/Common): 15/30 dB; measured UGF 340 kHz; phase margin > 50 deg. Notch at 770 kHz. Peaks at 1.77, 1.93, and 2.48 MHz up to within 2-3 dB of unity gain (see photo below). Probably should be addressed by rolling the loop off more aggressively above 1 MHz, or so.
- Frontend watchdog disabled at start of work, enabled at close of work.
Overall, loop seems to be functioning well.