Last night I measured the change in spherical power in ETMX during a 50 minute, 25.5W lock stretch (Started ~23 Jul, 00:05:00 UTC) using the same method last night's measurement,  see alog 19835.  The change in spherical power was 20 microdiopters, which means 21.2mW of power was absorbed.  According to the ASC_TR_X_A/B PDs the power in the arm was 132kW (+/- 15%), which puts the absorption in the ETMX at 160(24)ppb.  The absorption of this optic is 330ppb, according to the galaxy website, so our measurment does not agree with this previous value.

Attached is a plot of ETMX and ETMY spherical power change during this lock stretch.  There are some big glitches in the HWS spherical power, which correspond to where I briefly closed the green beam shutters. The ETMY spherical power looks dodgy.  I will adjust the misalignment of the green beam onto the ETMY and see if we can get a decent measurement.