Dhruva pointed out that there was a sudden increase in the amount of pump power going to the OPO to 15mW today. The power out of the SHG seems to have been constant, as well as the filter cavity green launch power and the OPO pump rejected polarization (on SQZT0). The only sign of something happening at the same time is that the ISS_OUTPUTMON had a sudden drop at the same time.
Was anyone working on SQZT0 or near the racks? I noticed that changing the ISS RF power sent ot the AOM no longer has a significant effect on the launch power, even so the RF monitor readback still reacts. This may indicate a problem with the cabling or the AOM itself. During the event the monitored RF power changed by ~0.5dB, maybe due to a change in the cable reflectivity?
This afternoon Dhruva and I went to SQZT7 and checked the AOM drive on the RF power meter. The drive to the AOM (measured at the table feedthrough) matches pretty closely with monitor (H1:SQZ-OPO_ISS_OUTPUTMON), within ~2dB. This seems normal, so maybe the AOM is broken.
| Drivepoint | digital readback [dBm] | RF power meter [dBm] |
| 1 | 13.7 | 12.3 |
| 0.07 | -1.8 | -3 |
| 5 | 26.85 | 2 |
Daniel pointed out that according to the datasheet, the AOM can only take 1.0W of RF power. At the time of death the AOM was at 31.8dBm (less if you believe the RF power meter over the readback) = 1.5W. We installed a UNAT-2+ attenuator at the output of the driver. The attenuator has a 1W max input so we might want to replace that with a beefier attenuator. Next week when we'll turn on the squeezer laser and go on table to replace the AOM, after that we will use the waveplate rather than the ISS for power control, and keep the drive to the AOM low.