J. Kissel, C. Compton

For historical documentation purposes, I was poking around TCS trends today looking for changes.

Camilla keeps excellent record of changes for all TCS settings, see LHO:70078 then LHO:70616 for all requested changes from April 2023's ER15 through May 2023's O4 start through June 2023's power down from 75W to 60W.

From these aLOGs, we know we want both TCS C02 lasers to deposit 1.7 W of annular power on the input test masses.

In confirming this, I was trending the TCS C02 Lasers and found that TCSX's laser power delivered to 
 - ITMX and ITMY took a 0.02 W step down on 2023-07-12 after 18:00 UTC failures of the site-wise laser interlock system (LHO:71276), 
 - ITMY was restored to 1.68 W after table incursion for HWS SLED replacement on 2023-07-18 (LHO:71476)
 - ITMX was also restored to 1.67 W after 2023-07-28 HWS SLED replacement on 2023-07-18 (LHO:71476) 
 - BUT ITMX C02 power delivered has trended slowly downward since 2023-07-18 from 1.67 to 1.57, a decrease of 0.1 W, to today, 2023-09-01.
     - There is a slight increase of ITMX power on 2023-08-13 09:18 UTC (02:18 PDT -- in the middle of the night on Sunday Morning), but
     - The loss of laser power resumes post CO2 laser chiller swap a few days later during maintenance day 2023-08-16 01:04 UTC (2023-08-15 18:04 PDT) (LHO:72220).

I attach a trend of the delivered power, as well as laser head power over the course of the run thus far.
The ITMX C02 laser head power is also trending downward, in slow discrete steps from 48.5 W to 44 W, a decrease of 3.5 W from 2023-07-18 to 2023-09-01.

I don't think the IFO cares about the loss of 0.1 W differential decay in delivered CO2 laser power, but the trend is perhaps concerning, and ITMX is decaying faster than ITMY.