Craig, Georgia, Varun
We had taken a measurement using Craig's template for SRCL dither to estimate the ARM power. We made the measurement at 47 W requested from the PSL and 39.6 W going into the PRM. We estimate the arm powers at ~330 kW in the X-arm and ~327 kW in the Y-arm
DARM/H1:ASC-X_TR_A_NSUM_OUT_DQ Arm Power Estimate = 327.640 +- 0.440 [kW]
DARM/H1:ASC-X_TR_B_NSUM_OUT_DQ Arm Power Estimate = 333.132 +- 0.463 [kW]
DARM/H1:ASC-Y_TR_A_NSUM_OUT_DQ Arm Power Estimate = 328.193 +- 0.528 [kW]
DARM/H1:ASC-Y_TR_B_NSUM_OUT_DQ Arm Power Estimate = 326.176 +- 0.459 [kW]
Results subjected to DARM calibration. We used the calibration at 25 W, which may not be accurate with the increased levels of power. We would need to revisit the arm power measurements with an updated calibration.
Here's a nice demonstrative plot of the sensitivity during this time.
Lots of caveats, but if you read between them, though, it's pretty impressive. Note the comparison between a time with a no sqz time in Sep 2020, before ITMY was replaced.
Caveats:
- This ASD is calibrated with the 2021-04-16 measurement of the sensing function which had 21.6 W of PSL power in to PRM. With that much more power last night in the arms, the optical gain and cavity pole could be quite different. However, if you compare (on this two orders-of-magnitude plot...) the PCAL line heights (green Xs) to live DELTAL ASD, you see the 410 Hz line matches, but the 1083 Hz line does not. Remember, 21.6 W in to PRM result said cavity pole was 451 Hz.
- Above 1 kHz, because the ISS second loop was not on at this time, we suspect the noise is dominated by intensity noise rather than show noise.
- Below 300 Hz, we made no effort to transition to any low noise operation, so we're still on high-range ETMX ESD, no low-noise ASC loop shaping, etc.
This result is not possible, likely due to overcoupling of the SRCL dither to radiation pressure from the high ASC noise at low frequencies. See alog 59142 for an explanation.