Naoki, Eric

Based on the FIS measurements in 77023, we thought that it was worth taking a look at the FDS for H1:LSC-SRCL_OFFSET1 = -275.  Unfortunately, we are unable to see any improvement in DARM relative to our nominal SRCL detuning.  We tried two SQZ angles chosen to optimize for mid-band and high freq squeezing respectively.  We did not have time to try tweaking the FC detuning, but we don't think it makes sense for this to be a FC detuning issue alone.  We were concerned that we might be fooling ourselves since the ifo had come unlocked early in the afternoon, so we checked the FIS trace again and it looked identical to earlier in the day.

We have reverted back to H1:LSC-SRCL_OFFSET1 = -175 for the observing period.

We have realized that our approach of optimizing the FIS spectrum for high frequency squeezing and looking for flatness was error prone.  We erroniously assumed that a reduction in low frequency RPN was desireable because it resulted in a flatter spectrum in the mid band and chose H1:LSC-SRCL_OFFSET1 = -275 accordingly.  In fact, we were adding an undesireable frequency dependent rotation with an unoptimal SRCL detuning which was rotating our injected squeezing away from driving RPN at low frequencies.    In the future, we will optimizing FIS for mid-band squeezing and attempt to tune the SRCL offset to flatten out the spectra at high and low frequencies (ie, eliminate any v-shape in the mid-band optimized FIS spetra).

New Datasets (all for H1:LSC-SRCL_OFFSET1 = -275) :

• 22:06:00-22:10:00 UTC - FDS spectra with SQZang = 195 (optimized for mid-band using SCAN_SQZANG script).
• 22:17:00-22:20:00 UTC - FIS spectra with SQZang = 207.  This looks the same as earlier in the day despite a lockloss in between (we were thermalized for ~2 hrs when taking this trace).
• 22:40:00-22:43:50 UTC - FDS spectra with SQZang = 207 (optimized for high freq squeezing by eye).