Francisco, Matthew, Sheila

Summary: We compared DARM noise before and after the vent. We see excess quantum noise above 800 Hz.

We wanted to quickly evaluate the squeezer after the vent. For this, we compared the DARM noise before and after the vent, with and without squeezing. Matt provided me the gps times at which our range was good with/without squeezing, before and after the vent, for four timeseries.

In the attached figure (sqz_compare_output), we plotted the ASD of GDS-CALIB_STRAIN_CLEAN (STRAIN_CLEAN helps on having a calibrated, reduced noise channel) for each timeseries, and the quadratic difference sqrt( post^2 - pre^2 ) for SQZ and no SQZ.

The ASDs with SQZ (red and purple traces) confirm a source of excess noise after the vent. The difference between the two ASDs (dashed brown and green traces) reveals an excess quantum noise above 800Hz. Jitter in the 200-400 Hz range make it hard to asses if the excess noise is quantum. We plan on taking 30 minutes of data next week to see if the pumps are affecting the jitter, i.e. making it worse and visible on the 200-400 Hz.

The plot was acquired with gwpy. The script to acquire and plot the data is found at /ligo/home/francisco.llamas/COMMISSIONING/scripts/sqz_compare.py