Since we have been struggling with the carm offset reduction sequence, here is a quick look at the data from our most recent lock compared with a model that I borrowed from Sheila, see alog 62110.
I plotted the TRX norm data versus the REFL LF data, normalizing REFL LF to the value it has when DRMI is locked only (3.7 mW). Here are the TR CARM offsets (uncalibrated) as well for reference
| TRX norm | REFL A LF (mW) | TR CARM offset |
| 4.68 | 3.65 | -3 |
| 33.3 | 3.58 | -8 |
| 42.2 | 3.55 | -9 |
| 808.63 | 1.96 | -40 |
| 1207.53 | 1.24 | -49 |
| 1359.8 | 0.885 | -52 |
| 1579.92 | 0.502 | -56 |
I found Sheila's code in the alog above, and added these data points to it to plot the transmission versus the refl dc power for different PRGs. This suggests, as we expect, that our PRG is quite high, the data points showing a PRG between 48 and 54. However, the very early points indicate a much lower PRG.
I also added Sheila's plot with the arm transmission versus carm offset in picometers. Based on our transmission, it seems that a "CARM 150 picometers" state, our CARM offset is actually pretty close to 150 pm. Similarly so for CARM 5 pm, assuming that our PRG is close to 54. These points are marked with stars.
Anyway, this doesn't really help us understand what's going wrong with the offset reduction.
