Naoki, Camilla, Vicky

For O4, we have swapped the CLF path's M5 mirror optic back its original 5:95 beam-splitter. This is the design (D1201210), and how it will be for O4. CLF ISS settings have been accordingly to our recent CLF ISS OLG measurements, with AOM RF @ 25.7dBm, and so ISS gain at 23dB (May 2023, LHO:69268). CLF_LAUNCH PD beam-splitter ratio has been updated and SDF'd according to our table measurements with the Thorlabs power meter (screenshot).

Some history of swapping the CLF BS/mirror:
-- July 2022. When we had the broken CLF fiber on HAM7 in Summer 2022, we replaced the CLF BS 5:95 to a mirror to get enough CLF power to lock, LHO:63893, ~July 2022.
-- Dec 2022. After fixing the fiber feedthrough, we swapped it back to the 5:95, LHO:66260.
-- Late-Jan 2023. LHO:67038, we swapped the CLF path back to a mirror to investigate how high-CLF levels can inject technical noise and limit squeezing.
-- Late-April 2023 68991+ 69084, Nutsinee and Daniel made interesting measurements of CLF intensity noise in DARM, related to RF AM at the CLF frequency, which is projected something like a factor of 8 below DARM. They installed an RF intensity noise monitor, LHO:69013, that'll live on SQZT0, so we can continue to monitor RF AM -- note: this intensity noise monitor is currently demodulated using the homodyne demod board e.g. SQZ-HD_DIFF_RF3_DEMOD_RFMON, so we will not be able to use the homodyne for now.
    -- Some summary alogs looking at CLF noise due to seeding or AOM RF drive power: LHO:67038, 67068, 67210. It seemed to us then that, driving the AOM at high RF powers was better.
    -- LHO:67219 Feb 2023, our most recent NLG sweeps on the homodyne measured up to 5.5 dB SQZ on HD, and suggested there was some technical noise about 10dB below shot noise, alongside ~25% loss and ~15 mrad phase noise.