John Z, TJ, Andy, David S, Ansel, Young-Min, Jess 

Summary: ETMX optical lever laser glitches are coupling into h(t) and causing high signal-to-noise ratio single-ifo burst and CBC triggers. We suspect the op lev sensor is coupling to h(t) through a damping loop for the L2 stage, as large spikes in the op lev laser power are coincident with spikes in L2 OSEM actuation in addition to h(t) glitches. 

Suggestion: The ETMX op lev laser or power supply should be swapped out ASAP. 

Hour-long clusters of glitches at 10-20 and 30-60 Hz were first noticed on Nov 18 in during a DQ shift earlier this week. The glitches seem to appear sporadically and can be seen in Omicron triggers on Nov 18 at about hours 12:00 and 18:00 UTC. The hveto algorithm, which looks for coincidence between glitches in h(t) and glitches in auxiliary channels, found the ETMX optical lever channels to be significantly correlated with these glitches. (Note the EX SUS rack magnetometer witnesses these glitches as well.)

Attached are two examples from Nov 18 of h(t) glitch correlation with spikes in ETMX optical lever laser power and L2 suspension control.

One of these optical lever glitches was the loudest single-ifo CBC trigger for LHO on Nov 22. They characteristically appear to be a few seconds long in h(t) and broadband, with similar time-frequency content to the optical lever PD signals: [h(t), optical lever (pitch)].