In-Vacuum Photodetector DC Light Levels
At 22W input with RC gain of ~50, we have
| Location | Light Level |
| LSC POP_A | 21.8 mW |
| LSC REFL_A | 9 mW |
| LSC POPAIR_A | 3.4 mW |
| LSC REFLAIR_A | 1.25 mW |
| LSC POPAIR_B | 2.0 mW |
| LSC REFLAIR_B | 2.8 mW |
| ASC REFL_A | 4.1 mW |
| ASC REFL_B | 4.1 mW |
| ASC AS_A | 2.9 mW |
| ASC AS_B | 3.1 mW |
| ASC AS_C | 0.15 mW |
| ASC POP_A | 10.2 mW |
| ASC POP_B | 9.5 mW |
| IMC REFL_A | 0.7 mW |
| IMC WFS_A | 0.33 mW |
| IMC WFS_B | 0.25 mW |
The LSC PDs have a calibration of 40V / 2^16cts / 200Ω / 0.76A/W = 0.0040 mW/ct.
The broadband PDs have a calibration of 20V / 2^16cts / 2000Ω / 0.15A/W = 0.001 mW/ct.
The WFS are RFEL have in low gain with 1kΩ transimpedance, whereas AS and IMC WFS are in high gain (10kΩ). WFS SUM calibration: 40V / 2^16cts / 1000(0)Ω / 0.76A/W = 0.000(0)8 mW/ct.
The QPDs have a calibration of 40V / 2^16cts / 2000Ω / 0.76A/W = 0.0004 mW/ct.
The POP beam towards the quads goes through a 90:10 splitter which dumps 90% of the light. The HAM1 POP beams goes through a 90:10 splitter which sends 90% of the light towards ISCT1.
The HAM1 REFL beam goes through a 90:10 and 1 50:50 splitter, which dump all but ~5% of the light. The next 50:50 splitter sends half towards ISCT1 and half towards the in-vacuum REFL path. The in-vacuum REFL path splits off 50% towards the LSC PD and 25% towards each of the 2 WFS.
The PR2 transmission is 229ppm,
See LLO equivalent table here.
Here are plots of the RF power readbacks of the demodulator boards at the REFL port. The units are dBm at the RF input. The sum of the WFS signals are roughly equal to the LSC PD signal (WFS have about a 1.5 greater transimpedance gain). However, the RF levels are extremly variable on the WFS segments with a min-max fluctuation of ~30dB.
Plot 1 shows a 4 hour minute-trend of the last lock stretch. Plot 2 shows a 2 minute interval of full data, however these are only EPICS readbacks. The LSC PD shows some peculiar upwards spikes.