Vicky, Naoki, Nutsinee, Daniel, Dhruva

With the IFO locked in nominal low noise today, we decided to check whether the filter cavity locking loops inject any length noise that turns into backscatter in DARM. In order to take this measurement, we first moved the RLF frequency to what we thought was carrier resonance in the FC. This frequency ended up being 104.66 kHz, about 2 kHz away from the frequency that we found on Friday (alog 66281). Not sure why this frequency moved so much. Before making any measurments, I used the ADF to try and align better to the IFO and we think the alignment isn't too bad right now. We have yet to optimize PSAMS.

We measured DARM with the FC locked in green near carrier. We saw some excess noise at low frequencies (could be the backscatter we were expecting to see). We iteratively tried to update our best estimate of where carrier resonance was by looking at DARM. We locked the FC in IR and saw this noise come down. At this point, it's still a bit hard to decouple what how much excess noise is coming from scatter and how much is related to squeezing rotation. This excess isn't very clearly visible when we're anti-squeezing either. This is the dtt screenshot with the aforementioned traces. Daniel also took a scatter measurement by dithering FC2 L at 40Hz while FC was locked on IR. The scatter was clearly visible in DARM, alog to follow..

Speaking of squeezing rotation, however, we think we have seen some solid evidence of frequency dependent rotation while we're injecting squeezing into the IFO!!!!! We moved the RLF up in frequency by 1 and 2 kHz to see whether we could see FDS and we did! The main issue, however, was that our non-linear gain and generated squeezing is way too low to actually see any real squeezing. But the frequency dependent rotation was super clear when we were antisqueezing, with the quantum noise dropping back to shot noise in the FC bandwidth.