[Aritomi, Yuhang]

Yesterday we tried many galvo servos for QPD2 DC centering, but no galvo servo can lock QPD2 DC centering loop. WFS2 DC signal either oscillates or goes away when we tries to lock.

We found that QPD2 DC signal moves a lot compared with QPD1 (attached movie). This may be due to larger beam size at QPD2 (farther from waist position). We measured spectrum of QPD DC signals without DC centering loop (attached screenshot). QPD2 DC signals are larger than QPD1 by a factor of ~2.

We also characterized beam size of green around QPD1 and QPD2 (Yuhang will report).