[Filiberto, Keita, ChrisW, Arnaud, Kiwamu]

We steered PR2 to get the beam on the center of PR3. Now we can see a beam hitting somewhere in the BS chamber. This beam spot appears to be the dark port beam.

Then one time, we were able to make the PR-Y cavity flash, but after some time of damping works, we lost it and never found it again. Tomorrow we are going to try a more systematic alignment. The attached is the alignment from the time when we saw fringes.

HAM3 spool Camera:

We first tried GigE cameras to look at the front surface of PR3 from the HAM3 spool position. This didn't work. The cameras were not so sensitive enough to resolve weak light. Then we removed a GigE and installed an analog camera on the 0 o'clock position on the spool. This then allowed us to see a spot on the PR3 cage as well as the swiss cheese baffle. We locally hooked up a monitor on the floor.

Later, Keita told me that it could be much more sensitive if we changed a gain in medm.

PR2 steering:

In the process of steering PR2, I found that PR2 kept tripping its watchdogs. It was due to the OSEMS hitting the open light threshold. I had to offload the alignment biases to IM3 and IM4 to mitigate this issue. The offloading worked well -- I was able to steer the beam onto PR3 while keeping the beam on both IM4 trans and POP_A. Unfortunately POP_B lost the beam but the recovery should be easy as we still have the beam on POP_A. The centering on PR3 was good in yaw and OK in pitch. I used scattered light from the lower part of the cage for aligning yaw and used the baffle to align the beam height. Also, PRM was aligned to obtain the retro-refletion back to PSL.

We got PR-Y flashing, but the spot seemed moving a lot:

Then we started steering PR3 by looking at the BS camera. The idea is to align the PR-Y cavity without wildly touching BS and ITMY which are thought to be a reference. Since I couldn't find a power cable for the illuminator on BS, the BS camera view has been simply dark. At some point, we found a moving spot out of this dark monitor. Because this spot responds to the angle of ITMY and BS, we believe this was the dark port beam which is now hitting somewhere in the BS chamber. By a yaw scan in PR3, we started seeing fringes in POP_A_SUM and REDL_A_LF. POP_A_SUM could go up to 10 counts when flashing while it is 5 counts nominally. However, the fringes didn't look stable -- sometime it didn't flash at all and sometime it flashed a lot. We suspected that something was moving and indeed PR3 was moving the spot position a lot. This was visible in the BS camera when we introduced an intentional offset in PR3 in yaw. The spot was moving vertically at about 1 Hz with an amplitude of approximately three beam sizes. Chris investigated why PR3 wobbled so much and eventually found that turning the HAM2 ISI on at level 3 made it quitter. After the investigating, we restored PR3 back. However we became unable to find the fringe any more. It is unclear what happened.