I looked again at DARM at 60W vs. 75W, comparing sqz and no-sqz for both. Each DTT trace uses 8 seconds, 50% overlap, 100 averages.

Lighter colors. 60W times used from 68251, w/15dB generated sqz.

• cyan,  FDS    @ 60W -  1364158671
• yellow, No SQZ @ 60W -  1364159804

Darker colors. 76W times from 6/4, ~3 hours into lock (semi-thermalized, past fast initial thermalization).

• red,    FDS    @ 76W  - 6/4 18:25 UTC
• purple, No SQZ @ 76W  - 6/4 19:00 UTC

See the summary page with this time window-- comparing red vs. black in this screenshot, I don't see obvious + excess noise with the squeezer on below 50Hz, when we are past fast initial thermalization.

Re: "fast initial SQZ thermalization" -- For reference, see the V-shape in blue that DARM takes with the fast 0.5-1 hour SQZ thermalization from a cold IFO (even unlocked for just 1-2 hours). Notably, in the first 0.5-1 hour, esp if the IFO was cold, the fast-thermalizing-SQZ (blue) exceeds the no-sqz noise (red) both below 50 Hz, and above 1kHz. I think this is related to the rapidly thermalizing SRCL detuning, which rotates squeezing across the band for the first 0.5-1 hour. To fix this SRCL detuning problem for sqz misrotation, I think we'd need to thermalize the SRCL offset; it wouldn't be sufficient to thermalize the sqz angle. If we have to pick an angle, we should pick the sqz angle that optimizes the bucket noise ~100 Hz; this is the most stationary as SRCL thermalizes. I think for calibration, Jeff sees this too as wildness in the rapidly thermalizing sensing function at the start of locks. This effect seems more prominent from an cold IFO, as it seems more muted of a V-shape when IFO relocks quickly (not much down/cold time).

Note the excess noise 20-50 Hz in the 60W vs. 75W configuration. Brina is now looking into understanding the calibration status and LSC coherences for these sqz and no-sqz times.