Jenne found that;
0. If all mirrors are "aligned," Yarm flashes.
1. If SRM is misaligned, Yarm doesn't flash.
2. If BS is misaligned, Yarm doesn't flash.
3. If ITMX is misaligned, Yarm still flashes.
So, my hypothesis from this is that I was playing with " TT1 -> TT2 -> ITMY -> BS -> SRM -> BS -> Yarm " configuration last night.
This hypothesis can explain;
1. Why I could not get TRY peak more than 0.5 (additional BS reflection makes incident power to Yarm less).
2. Why I had to change POY11 I/Q mixing angle by ~ 45 deg (because EOM to Yarm length changed).
3. Why I couldn't lock Yarm stably (additional reflection by BS and SRM made too much beam jitter?).
We are now trying to get "real" Yarm flash.