Sudarshan, Gabriele
Since yesterday we were not able to move the beam on the ISS QPD or PDs using the picomotors, today we tried to use IM3 to change the beam position. In brief, we are able to see a change in the QPD signal when we move IM3, so it seems there is a beam on the QPD. We read a sum of about 830 count on the QPD, which corresponds to 0.5 V. The transimpedance should be 100kOhm, so the power on the QPS should be of the order of few microwatts, while we expect 1% of the total power going into the ISS box, which should be more like 0.1 mW.
We couldn't see any change in the mean value of the PD signals, however the RMS could be changed a lot, see the striptool trace. The initial position of IM3 was: PIT 55500, YAW 2600. The one corresponding to the largest RMS in the PDs was PIT 59500, YAW 1600.
The second plot shows a comparison of the PD spectrum (dewhitened) in the original position (red) and in the new position (blue). There is significantly more signal in the new position.
In summary
- If we move the beam into the ISS box we can change the level of signals on the PDs
- There still seems to be too low power, even on the QPD
- We were not able to move the beam using the (old) picomotor, so this is likely not working
