Comparing the buildup of H1:LSC-POPAIR_B_RF18_I_ERR_DQ between Nov 2025, at GPS time 1447346785, POPAIR RF18 I has a maximum of 168 counts. Today, while locked at PRMI with the buildups maximized, the same channel has a maximum of 62. This means that we are missing more than 70% of the power along this path.
We have previous trends from Ryan S and Ryan C, but they might have trended a normalized channel, which is confusing because the input power and the way we power normalize these channels has changed. Comparing the ERR channels is more straightforward.
POP A LF maximum was about 88 and now it is about 32.
Referencing these alogs: 91622, 91528
Keita has also confirmed that the whitening gains and digital gains of POPAIR RF18 and the modulation depth settings are all as they should be between these two times.
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I also looked up a MICH dark time since we are getting very confused about what power we actually are or are not missing. Here is a table summary:
MICH DARK: 1432426657, ALIGN IFO STATE 43, May 28 2025
| Channel | Value | Units | Notes | Value Now | Ratio Now/Then |
| IMC-IM4_TRANS_NSUM_OUT16 | 9.42 | W | 9.22 W | 0.98 | |
| LSC-POP_A_LF_OUT16 | 4.5 (max) | uW | maximum power, BS was being moved by hand during this time (checked aligment sliders) | 3.83 uW | 0.85 |
| LSC-POPAIR_B_LF_OUT16 | 1.04 | ct | 0.65 ct | 0.63 | |
| ASC-POP_X_DC_NSUM_OUT16 | 0.28 | ct | I multipled by the normalization factor of 407 so this value is comparable to now, no PM1 centering engaged I think, but segments look well-balanced so the beam was close to center of diode | 3.02 ct | 10.8 |
Here is a table summary of the PRMI time:
PRMI locked: 1447346762, ISC_LOCK state 52, Nov 16 2025
| Channel | Value | Units | Notes | Value Now | Ratio Now/Then |
| IMC-IM4_TRANS_NSUM_OUT16 | 1.84 | W | 1.83 W | 0.99 | |
| LSC-POP_A_LF_OUT16 | 88 | uW | 30 uW | 0.34 | |
| LSC-POPAIR_B_LF_OUT16 | 17.8 | ct | average value | 5.5 ct | 0.30 |
| ASC-POP_X_DC_NSUM_OUT16 | 35.4 | ct | I multipled by the normalization factor of 407 so this value is comparable to now, PM1 centering was engaged | 129 ct | 3.6 |
| LSC-POPAIR_B_RF18_I_ER_DQ | 167 | ct | average value | 52 ct | 0.31 |
Conclusion:
Sheila and I think that the MICH dark numbers actually hang together. This is further bolstered by the fact that we can only make marginal improvements to the alignment onto POP diodes with picoing the HAM3 pico. We think the larger discrepancy in the popair diode in MICH DARK can be accounted for by the fact that the beam is close to the edge of the periscope mirror. We also manage to make the ALS alignment worse with the pico. Therefore, we think the pico alignment is fine.
However, the PRMI numbers clearly indicate a problem, but this points to PRC clipping instead.
Adding two more columns and a row to Elenna's table showing that on July 23rd afternoon, we were at MICH DARK locked with LSC-POP_A_LF_OUT16 at 7uW, plot.
| Channel | Value O4 May 28 2025 00:15UTC plot | Units | Value Now plot |
Ratio Now/O4 |
Value 23 July 2026 23:45UTC plot | Ratio July/O4 |
| IMC-IM4_TRANS_NSUM_OUT16 | 9.42 | W | 9.22 W | 0.98 | 8.68 W | 0.92 |
| LSC-POP_A_LF_OUT16 | 4.5 (max) | uW | 3.83 uW | 0.85 | 7.2 (max) | 1.6 |
| LSC-POPAIR_B_LF_OUT_DQ | 1.04 | ct | 0.65 ct | 0.63 | 0.84 ct | 0.80 |
| LSC-POPAIR_A_LF_OUT_DQ | 1.85 | 0 |
Interesting to note that the May time we were still recovering from the HAM1 vent. e.g. 84648
