[Alexa, Kiwamu]
Since the main laser got back running (alog 6551) we attempted to resume the WFS commissioning this evening.
However in the middle of acquiring the lock of IMC the reference cavity lost its lock and never came back again. It seems that the reference cavity got misaligned a lot so that the autolocker is unable to capture 00 mode. In fact it tries to capture the 01 mode instead. The alignment needs to be fixed.
MC1 and MC3 alignment biases:
We found that the MC1 and MC3 alignment biases had changed due to the restarting of the realtime model (alog 6531) yesterday. We brought the M1 alignment biases back to where they used to be before the restart. This recovered the alignment and we got IMC flashing. Besides, we found that the damping loops on MC1 wasn't enabled and we turned them ON to get a stable alignment.
WFS-B position shifted:
In order to have two WFSs afar from the beam waist by a Gouy phase 0f 45 degrees, WFS-B needed to be at 709.7 mm from the lens L3. According to Cheryl (alog 6521) WFS-B was at 679 mm and hence needed to come further by 30.7 mm to get the right Gupy phase. At first we double-checked Cheryl's optical path length measurement and our measurement agreed with hers. So we simply shifted WFS-B toward the north so as to increase the distance by 30.7 mm. I believe that the precision of these positions is about a few mm.
The attached shows our WFS location strategy. Since the horizontal and vertical profiles are slightly different we wanted to place WFS-A at (347.4 + 407.2) / 2 and WFS-B at (708.8 + 710.6) / 2. Because WFS-A was already in a good place, we simply shifted WFS-B which had been at 679 mm. The plot is essentially the same as the one Chris posted before (alog 6439), but since there was a minor mistake in the Gouy phase plot, I put the corrected version here.