richard.savage@LIGO.ORG - posted 11:53, Tuesday 07 October 2014 - last comment - 08:42, Wednesday 08 October 2014(14338)
H1 PSL FSS path maintenance work
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.
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Isomet AOM 1205C-843 S/N 120684, purchased under P/O S127984. Replaces the AOM purchased during the Initial LIGO era.
Plot of the reference cavity transmission and pre-modecleaner output after the work on the AOM. There are two discontinuities in the reference cavity transmission. The first probably coincides with the FSS oscillations noted by Kiwamu earlier today. The second change might be due to the common gain being reduced to 18.8 from 30.0.
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