Measured IFO beam self-heating absorption, using data form Saturday April 1st when Dan had an IFO lock with CO2s off. CO2's had been off for 6 hours, and the IFO had been locked for 2h30, see attached plot of thermal state. A better method was used in alog 66098, I'll work on how to use correctly this with Dan/Cao.
See attached plot made using Aidan's absorption plot script (instructions in TCS wiki) in /ligo/gitcommon/labutils/hws_absorption_fit/april2023.
ITMX and ITMY: ~128mW absorbed = 350ppb (128mW / 363kW arm power from H1:ASC-{X/Y}_PWR_CIRC_OUT16). Coatings are expected to have 0.5ppm (500ppb) coating absorption.
We've previously measured significantly higher absorption on ITMX, which has known point absorbers, not sure what's changed apart from significantly higher circulating power - 360kW rather than 230kW. Previously measured:
| April 2022 (62468, 62782) | Nov 2022 (66036) | April 2023 | |
| ITMX | 430ppb | 490ppb | 350ppb |
| ITMY | 370ppb | 385ppb | 350ppb |
Using Dan's /ligo/gitcommon/labutils/hws_absorption_fit/april2023/fit_absprtion_v2.py from alog 66098, which takes into account the center of the IFO beams (should be updated in channels HWS_ORIGIN_{X,Y} but wasn't at that time). This shows that absorption is close to what was previously measured, plot attached:
| April 2022 (62468, 62782) | Nov 2022 (66036) | April 2023 | |
| ITMX | 430ppb | 490ppb | 475ppb |
| ITMY | 370ppb | 385ppb | 375ppb |
H1:TCS-ITMY_HWS_ORIGIN_X/Y = (515,566), updated from April 1st value of (491,566) on 12th April*
* Looking at the last few locks the IFO beam position on ITMY has slightly changed in YAW since April 1st, see attached for IFO beam center difference between start of April and now, with old (491,566) center plotted as red cross.
