Robert, Sheila
During the long earthquake yesterday afternoon we centered the IMC WFS. (We didn't measure the spot positions in the IMC before and after because of a problem with the script, which Craig has now fixed.) Then Robert and I calibrated them by making a PZT excitation with the IMC unlocked and MC2 misaligned, and repeating the measurement with the IMC locked at 2W input power.
We used the ratio of the transfer function of the PZT to the DC signals when the IMC is unlocked (multiplied by sqrt(pi/8)) over the measured transfer function to counts of the RF signals (or locked DC signals) to calibrate counts of the locked signals into beam diameters.
The templates that we used are in /ligo/home/robert.schofield/templates/IMC_PZT
We found:
| pit (beam diameters/count) | yaw (beam diameters/count) | |
| A I | -2e-3 | -6.8e-3 |
| B I | 5e-5 | -1.3e-4 |
| A DC when IMC is locked | 8.3e-2 | 8.3e-2 |
| B DC when IMC is locked | 4.0e-2 | 4.2e-2 |
In the past, see alog 34845, the difference between locked and unlocked was closer to 1/3. Here it is closer to 1/2. Could this be power dependent?