Jennie, Jenne, Elenna, Vicky, Erik

As referred to in this entry we took a suite of measurements on the 3rd May to determine what changing the SRCL offset, DARM offset and turning off the whitening on DCPD would have on the sensitivity.

Measurement Order: from 05/03/2023

• Elenna measures contrast defect.
• Measure SCRL1 offset and optimise, see this entry.
• Vicky optimised squeezing.
• Elenna took BB PCAL > DARM measurement.
• Change DARM offset to 40 mA.
• SRCL1 offset measured and optimised.
• Elenna took BB PCAL > DARM measurement.
• DCPD whitening off.
• Elenna took BB PCAL > DARM measurement.
• Change DARM offset back to 20 mA

At low frequencies DARM looks better with 20mA offset, but we must remember that many things at low frequency are optimised for this DARM offset. See first plot for 20mA/40mA comparison.

The whitening ON/OFF (see second plot attached) does not look to have made a large difference to the sensitivity from these plots.

There is no coherence in the PCAL > DARM BB measurements we took at high frequency so to give us a good idea of the difference between 20mA and 40 mA DARM offset we will scale the DARM spectra using the one of the high frequency calibration lines.

Unfortunately, we did not spend any time in NLN with 40mA (just NLN CAL MEAS) so we will need to measure another DARM spectra in that state today.

The code I used to correct the DARM spectra with the PCAL to DARM measurements is in /ligo/home/jennifer.wright/git/DARM_offset

• Run_DARM_calib_20230503.ipynb runs the analysis.
• reference_times/reference_times_pre_O4.yml contains the measurement dictionary.
• Measurement data locations are listed in the table above.
• I used PCal_bb_inj_quick_cal.py by Craig to process the measurements but I had to alter it to use a DTT xml file reader that Erik wrote (reftf.py), as some of the TF measurements referenced in the .xml file were missing their B channels. Note: only an issue if you try to read directly from xml, I could still export the measurements as text files.