Reports until 18:02, Wednesday 03 July 2019
H1 ISC
jenne.driggers@LIGO.ORG - posted 18:02, Wednesday 03 July 2019 (50380)
Sensing function vs. ETMY spot position

[Jenne, JeffK, Sheila, MatthewB, Adrian]

We're having a look at what the effect is of moving the beam spot position on the optic that we use for Pcal (ETMY).  This is similar to the first attempt we made at the end of May in alog 49541, although there we were moving the spot on ETMX (our DARM actuator).  As we move the spot, we are taking the standard calibration sensing function measurements to see how the spot position change affects the measured sensing function.

Our latest thought with these data is that in fact the sensing function is changing as a function of spot position.  The 1/1+G parts of the measurement seem to change at low frequency, because they include C the sensing function.  The C/(1+G) part of the measurement doesn't seem to change at low frequency with different spot positions, but this is because with large G the Cs cancel on top and bottom of the fraction, leaving the measurement looking like 1/(A*D).  So, we're taking PUM and ESD measurements at the extrememely non-nominal spots, as well as the nominial spots, to confirm that those aren't changing.  The attached plots below show that the sensing function is changing at low frequency as we change the spot positions via the A2L gains.

Non-image files attached to this report