The power meter was installed in GRMC transmission in order to align the MZ. First I blocked the PZT arm of the MZ and aligned using the MZ mirror and subsequent steering mirror to optimise mode matching from GRMC transmission. Then I blocked the non-PZT arm and aligned the MZ to GRMC again. Afterwards I adjusted MZ offset on the high voltage driver to get the intereference condition that outputs TEM00 from the main MZ path and TEM10 from the rejected path. Currently we have:

TEM00 1540 mV
HOMs 56, 32, 12 mV
Mode matching = 1540/1640 = 94%

One time I noticed the level of TEM00 slowly going down over a timescale of minutes. Adjusting the MZ offset brings it back to where it was. Maybe something is drifting slowly?