[Stefan, Lisa, Evan, Kiwamu]

Our goal tonight was to get the IR transmitted light centered on the transmon QPDs. A coarse alignment was established. We still need to do a fine alignment with the picomotors.

QPD centering:

We had never aligned this path with the actual IR beam, and neither QPDs had a beam on them. As discussed and suggested in the last integration meeting, we started this mission from a scan of the TMS in order to find an IR beam with the QPDs. Moving the TMSX in an almost random way, we found a beam which was flashing as the carrier light resonated in the cavity. The yaw angle needed to be twisted by roughly 100 urad to get the beam on the QPDs. Then, keeping the flashing beam on the QPD by steering the picomotors (M4 and M14), we steered the TMSX back to the nominal angle. This operation was successful. Then we moved onto a fine adjustment by locking the main infrared light to the arm cavity (the detail of the locking procedure can be found in alog 9644).

The fine tuning was very frustrating. We kept loosing the lock because of the roll mode of MC2 at 40 Hz (see awiki for HSTS resonances ) which then saturates everything and breaks the lock. Plus the spot position on the two QPDs didn't seem to be conversing by moving a combination of the two picomotors. The spot behaved as if the picomotors are degenerate. It is possible that, since the time for tweaking the picotomors was limited by the stability of the locking, we confused ourselves in the rush. This needs to be revisited. Anyway, a good news is that we now have a beam on both the QPDs and therefore we can do the fine adjustment anytime when we get a chance.  Also we did an estimation of the power on the QPD, because we needed to clarify if the beam we saw was the main beam or a ghost. This is summarized in Evan's log (see alog 1006).

Some other things:

Later tonight, I tried to engage the AO path. Though I haven't succeeded. The idea is to have a low cross over frequency which then allows us to (re)insert the notch filter for the 40 Hz roll mode. However the loop was not so stable and everytime when I changed the AO path gain in the common mode servo board it simply broke the lock even if the gain seemed small enough. In addition to it, it became harder to lock approximately after 1:30 am probably due to some angular fluctuation in the arm cavity. I am too lazy to identify what optic is moving, but it is also clearly visible in the green ISCT1 CCD camera. Because of that, the IR locking doesn't stay more than 2 seconds -- the cavity build up in infrared drops extremely quickly due to the angular fluctuation.