I measured the arm cavity losses as Kiwamu did way back in ELOG 5074.
I used the same logic as the ../scripts/LSC/armloss script, but did it manually. This meant:
- Lock and ASS-Align both arms.
- Misalign the ITM of the arm that I'm not measuring, to get its spot off of AS
- Take 10 seconds of ASDC_OUT data while the arm is locked.
- Unlock, misalign ETM of arm of interest, take another 10 seconds of ASDC_OUT
- Relock, run ASS, goto #3
Analysis was done similar to ../scripts/LSC/armloss.m. This uses the nominal T values (.014 and 15e-6) to estimate the input power from the unlocked ASDC data, and the cavity reflectivity from the locked ASDC / input power. Then, loss is calculated by:
- Pin = ASDC(unlocked) / R1
- Rc = ASDC(locked) / Pin
- rc=sqrt(Rc), etc.
- Loss = 1 - (( 1 / r1r2)) * ( 1 - t1^2 r2 / (r1 - rc)) ^2
I did this for pairs of locked / unlocked data stretches. (Subsequent pairs maybe have slightly different things going on, but each pair was taken within a minute or so of each other)
Unfortunately, during the X Arm measurements, the MC was misbehaving with large REFL fluctuations, so I don't have confidence the results.
The Y Arm data seems fine, however.
The Y arm loss is 123.91 +/- 10.47 ppm
(Trial-to-Trial fluctuations dominate the fluctuations within each trial by far, and their standard deviation is what I report as the random error above)
This seems roughly in agreement with old values I've seen in the ELOG. I'll remeasure the x arm tomorrow during the day. Here's a plot showing the ASDC values of the Y Arm measurements.