I have spent some time today trying to get decent interferometer alignment.

The goal today was to get good PRMI alignment while maintaning the POP beam at ISCT1. I could obtain good alignment only in pitch. The yaw alignment still needs to be touched up. 

(background)

Even though we managed to get the POP beam extracted at ISCT1 (see alog 13547), this resulted in bad alignment in the PRMI.  We basically could not flash the PRMI without loosing the POP beam if we touch a single optic to align the PRMI. So a combination of some optics needed to be touched up.

(What I did)

Since the Michelson had been already (kind of) aligned, I assumed that ITMX is well-aligned. Also, I assumed PRM and IM4 to be already aligned (this may not be true -- I should have carefully checked IM4 and perhaps other IMs). Under these assumptions, I tried to aligning PRX. Note that I misaligned ITMY and BS during the process. I touched PR3 and PR2 in pitch to find an optimum alignment. Doing some iteration, I got a good alignment. The attached is the resultant alignment. This alignment maintains all the signal ports including REFL, POP and AS. However, since only pitch is optimized, this configuration does not allow the PRMI to flash yet. In order to flash the PRMI, one needs to steer yaw of some optics. For example, one can change yaw of PR2 from 3640 urad to 2179 urad to flash the PRMI. No pitch adjustment is required.

Also, I tried the same iteration process in yaw. But this did not seem successful for some reason. As I aligned the combination of PR2 and PR3, it seemed that the beam started hitting the right hand side of the PR3 cage. And indeed the amplitude of the demodulated signals decreased at REFL. The work continues.