Matt, Lisa, Craig

Previously I had made some in-loop green frequency noise measurements of ALS_COMM and ALS_DIFF.
Today we made some out-of-loop IR frequency noise measurements.

First we locked green to the Xarm in LOCKED_SLOW_W_ETM_WFS, then IR to the Xarm via the XARM_IR_LOCKED ALIGN_IFO guardian state, so that IR had control of MC2.  Then we measured the frequency noise of transmitted green light beating with frequency-doubled IR on ALS_COMM using the COMM PLL.  The COMM PLL is calibrated into micrometers, so I calibrated it back into IR Hz and plotted it below.

X-arm IR Frequency Noise RMS = 12.4 Hz = 180 pm

We have some concerns about this measurement, in particular, we are missing some peaks present in Alexa's measurement of the same frequency noise (Figure 6.1 of her thesis).  LHO alog 10511 gives their old method of estimating IR frequency noise.  Our measurement scheme today is closer to LLO alog 11265, only we locked using POP_A_45 instead of AS45.