camilla.compton@LIGO.ORG - posted 10:45, Thursday 18 September 2025 - last comment - 15:13, Thursday 18 September 2025(87002)
DARM Offset Step Ran
Elenna, Camilla
We ran auto_darm_offset_step.py after activating labutils following Jennie's 86623 instructions at ~17:30UTC to 17:45UTC. We left the POP beam divertor open and did not turn off the OMC ASC. We were in No SQZ at the time.
Comments related to this report
camilla.compton@LIGO.ORG - 11:36, Thursday 18 September 2025 (87003)
I processed both measurements. With OMC ASC ON, the fit gives a contrast defect of 0.77-0.86 mW. However with OMC ASC OFF, the fit gives a contrast defect of 1.23-1.28 mW. I am confused, because the motivation for running with the OMC ASC off was "the OMC ASC goes bad when we changed the DARM offset and this makes the measurement worse".
I tried to look back at previous contrast defect measurements. Jennie measured the contrast defect in June while adjusting CO2 annular power 85434. Her measurements report values ranging between 1 and 1.1 mW for different CO2Y powers. Not sure if those are directly comparable, given her changes of the CO2s. I also believe she has been running these measurements with the ASC off.
I measured the contrast defect with the OMC ASC ON in 80804 (circa October 2024) to be 0.742 mW.
Just comparing the ASC ON measurement from the October measurement, the contrast defect has possibly gotten worse. Comparing the measurement at the 255 Hz line, the contrast has increased by 16% (0.862/0.742). Comparing the data measured at 410 Hz, the contrast defect is the same (0.771/0.771).
Repeated at 18:20 to 18:35UTC with the OMC ASC off.
I processed both measurements. With OMC ASC ON, the fit gives a contrast defect of 0.77-0.86 mW. However with OMC ASC OFF, the fit gives a contrast defect of 1.23-1.28 mW. I am confused, because the motivation for running with the OMC ASC off was "the OMC ASC goes bad when we changed the DARM offset and this makes the measurement worse".
I tried to look back at previous contrast defect measurements. Jennie measured the contrast defect in June while adjusting CO2 annular power 85434. Her measurements report values ranging between 1 and 1.1 mW for different CO2Y powers. Not sure if those are directly comparable, given her changes of the CO2s. I also believe she has been running these measurements with the ASC off.
I measured the contrast defect with the OMC ASC ON in 80804 (circa October 2024) to be 0.742 mW.
Just comparing the ASC ON measurement from the October measurement, the contrast defect has possibly gotten worse. Comparing the measurement at the 255 Hz line, the contrast has increased by 16% (0.862/0.742). Comparing the data measured at 410 Hz, the contrast defect is the same (0.771/0.771).