Ushiba, Dan, Nishino

Alignment improvement

We adjusted the alignment of Gr M4 (see POP layout) to maximize the error signal amplitude (Michelson fringe) and it was improved from ~1000 to ~2000 counts.

The lock was stable for ~1 hour in this state (without thermal feedback).

But after that, the lock became unstable and the error signal amplitude has become ~1000 counts again.

GRX DCPD calibration

Count: 1772 counts (bacground=5.5 counts)

Power right after the GR fiber: 9.93(1) mW -> calibration factor = 5.62e-3 [mW/count]

Power in front of the GRX DCPD: 0.71(1) mW -> calibration factor = 4.02e-4 [mW/counts]

Open-loop function of FIB servo

The measured open-loop function of the FIBX servo is below.

UGF is ~7.5 kHz and the phase margin is ~ 43 degrees.

We could see the tweeter's resonance at 58.912 kHz.

Small change; PDA1 the gain 

We noticed that the gain knob of PDA1 in the PSL room was halfway between 30dB to 40dB. We fixed it to 40dB and did not see any significant change in the output signal.