As was described in alog 13761 (see the addition to that entry) it seemed as if what we see in the POP sled QPDs are not what we expect.

As it turned out, the sled was badly off in YAW such that the beam doesn't come to the sled without using picomotors. I needed to use "magnum" step for moving picomotor in YAW. What we "saw" previously seems to be a lobe of severely clipped beam.

Anyway, using a straight shot beam I'm already getting 1551 counts of H1:ASC-POP_A_SUM_OUT and 1450 counts B (whitening gain 45dB), while the maximum we should get is about 1540 counts assuming 10W through IMC, 3% PRM, 229ppm PR2, 10% through attenuating BS, 1k transimpedance, 45db whitening and 0.8A/W responsivity.

(I'm not using "toW" filter, so these SUM numbers are raw counts.)

Note that centering on QPDA is sort of reasonable, so you should be able to use that reliably for the carrier buildup measurement, but on QPDB the beam is only on one quadrant (S3). I'll continue centering tomorrow.