craig.cahillane@LIGO.ORG - posted 14:06, Wednesday 18 July 2018 - last comment - 18:06, Wednesday 18 July 2018(42957)
ALS X PDH and PLL Spectra
I went down to X end and repeated the ALS measurements done for Y end. ALS X green visibility is 30%. Free swinging PDH peaks give ~750 mVpp demodulated reflection response. With a cavity pole of 275 Hz, we roughly calibrated the PDH error signal with 2*cavityPole/PDHvolts = 733 Hz/V. Plot 1 PLL UGF is 27 kHz PDH UGH is 8 kHz Plot 2 PLL error spectrum Plot 3 PDH error spectrum Plot 4 Estimated transmission frequency noise from PDH error spectrum with arm pole applied. In loop ALS X Transmission Frequency Noise RMS is 1 Hz. Now that ALS COMM is locking, we will get an out-of-loop measurement of ALS frequency noise soon.
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Took a quick look at ALS COMM PLL output to estimate what kind of frequency noise we're seeing. The channel H1:ALS-C_COMM_PLL_CTRL_OUT_DQ is already calibrated into micrometers. I uncalibrated it back to Hz for the plot below. ALS COMM RMS = 25.8 Hz = 183 pm
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