Sheila, Jennie W

During commissioning window today we measured the P2L and Y2L gains for the PR2 mirror.

This is part of the work to understand how to move the beam on PR2 in order top avoid a reflection and subsquent stray beam off the PR2 scraper baffle (as found in alog #77631 by Annamaria and Robert).

The P2L gain was close to optimised and has been left at -0.36.

The commissioning window ran out before I could finish optimising the Y2L, I have left it at -7.00 which gave better A2L decpupling than the previous value.

Method:

• Inject line on PR2 M3 stage pitch at 30Hz using the OSC 9 filter bank in the ADS.
  • sitemap-> ASC -> Dither overview
• Check the PIT9 filter bank at the bottom of the page is not being used (CLK gain = 0).
• Set the matrix at the right of the row to have a 1 in the PIT9 to PR2 cell.
• Check there is a ramp time in the PIT 9 filter bank.
• Set the frequency to 30 and step the amnplitude to 1 in a couple of steps.
• Measure a reference for DARM and PRCL. The red and blue traces show the case when injecting into pitch with nominal A2L gains.
• Set the aevraging to exponential and zoom in on the line.
• Change gain in HzTS->PR2-> M3 DRIVEALIGN->P2L

 Do this until the line height relative to the background is minimised, allowing time for the ramp and a couple averages each step. One thing to note is that the line height above the background in the PRCL spectrum (LSC-PRCL_OUT_DQ) is much less than the relative height above the background in DARM which suggests that the noise in PRCL is not coupling strongly to DARM.

Switch off the line and set the PIT 9 amplitude to 0 counts.

Then repeat the above for the YAW 9 oscillator channel in the ADS, changing the gain in the Y2L gain filter bank in order to minimise the line height. The reference values for yaw are in the photo linked above with the green line showing DARM (we had gone into NLN cal meas with SRCL FF switched off for Elenna's SRCL tests so that is why DARM shows elevated noise). The orange line is the reference value of PRCL using the nominal Y2L gain. The same amplitude was used in the oscillator for this line but it was much higher above the PRCL background noise than for the pitch degree of freedom.

Template is at /ligo/hom,e/jennifer.wright/git/2025/A2L/20250113_A2L_PR2.xml