Naoki, Camilla, Sheila

Today we saw bad high frequency squeezing we recently have at the beginning of the lock as reported in alog73798. We reverted the CARM gain to nominal today, so the bad squeezing is not related to the CARM gain. We could recover high frequency squeezing by rotating the sqz angle, which means the sqz angle was not optimal at the beginning of the lock. However, the squeezing level was less than 4dB even after sqz angle optimization. We suspect that this worse squeezing level is related to ZM alignment change we recently had.

The first attached figure shows the ZM4/5/6 alignment for the past 9 days. We had 4.4dB squeezing a week ago, but ZM4/5/6 alignment changed 6 days ago during SQZ-OMC mode scan in alog73696 and we cannot recover 4.4dB squeezing after that.

We turned off SQZ ASC and walked ZM4/5/6 sliders to maximize the rms of ADF at OMC transmission with anti squeezing. The second attached figure shows that we could recover 4dB squeezing after ZM alignment change. To recover 4.4dB squeezing, we would need to revert the ZM4 alignment to the values a week ago.