Summary:

Looking at ITMx HWS data from full interferometer locks on 7 Feb and 9 Feb, here are some estimates of ITMx coating absorption:   500(150) parts per billion measured on Feb 7,  9 Feb: 430(130) ppb measured on Feb 9.  For reference, Livingston measured 140-200 ppb coating absorption on the ITMs, see log 14634.

Method:

-HWS measures spherical power.  The raw data was multiplied but a factor of 0.00326 in dataviewer to account for magnification of the image, which gives Spherical power in diopters.   The change in the spherical power before and after the interferometer drops lock was ~5*1(0.02) microdiopters both days.  The measurements were averaged over a few minutes.

-The shperical power is related to absorbed power by 1.06(0.3) mW/microdiopter (log 14634) which means ~5mW power was absorbed.

-On 7 Feb 10.4 kW was in the x-arm, on 9 Feb 11.5 kW was on x-arm (calculated as per alog 16579).  I've assumed 10% uncertainty on this power, but perhapse that is too small.

[absorption in ppb]=[absorbed power]/[locked arm power] *1e9

Datasets and code are saved in /ligo/home/eleanor.king/HWSreadouts.