Yuhang and Marc

We found that the SHG is misaligned this morning. This misalignment cannot be corrected by only tilting the steering mirrors before SHG. This is a bit strange for us. The situation of the misalignment is shown in the attached figure.

It was found later that this is caused by: the small scan amplitude of the locking servo.

The scan amplitude is adjusted to be small so that the lock loop can be engaged around the TEM00 resonant peak. However, today, due to the drift of cavity length, the small scan range is located accidentally around the first order resonance peak. This created the confusion at the beginning.