Thomas V. & Szymon S.

Over the last couple weeks we have noticed that the ETMY optical lever power monitored on the channel H1:SUS-ETMY_L3_OPLEV_SUM_OUTPUT has been periodically fluctuating. The monitored power level has been dropping from a nominal 10,000 counts to 0 counts on a regular interval. Exchanging the power supply on May 3 seemed to have slightly improved the situation with the power level dropping to 6,000 counts from 10,000, but still on a very regular schedule. I tried another spare power supply as well as using a different cable connecting the laser with the power supply. Attached is a plot of how the power level read from the quad photodiode varies after the last change on May 15, still fluctuating.

Testing the power supply pins with a voltmeter I saw the voltage at a steady 5 volts, and no regular power glitch as seen on the oplev sum. Additionally, the laser module for ETMY optical lever is loudly buzzing most likely due to the cooling fan interfering with something inside the chassis.

The ITMY optical lever was installed and aligned a week ago, but has drifted significantly since initial alignment. One theory is that the cables for the electric micrometer stage are forcing the stage holding the QPD to move around. ITMY optical lever plots show that the laser power is wandering in a sawtooth pattern, probably due to drift of the stage.