Camilla, Wen

Last Friday, we had two problems: the pump-CLF had trouble locking after we moved PZT2 from FC SLOWOUTOFS to CLF SLOWOUTOFS (see Daniel's 65510). The green FCGS REFL power is somhow 6x lower than before (65498). They are all fixed today.

The OPO locking wasn't working well until we realized that the pump REFL power was reduced. We examined the OPO REFL PD and found that the beam was clipped on the PD. This is perhaps due to the work on FCGS path when we might actually bumped the periscope mirror of OPO REFL path. After realigning the beam to the center of PD, the locking is working but on the wrong resonance. The second trigger for CLF resonance was too low. With the maximum level of 72 while on resonance, we've set the second trigger level from 0.5 to 50 on guardian (H1:SQZ-OPO_PZT_1_SCAN_TRIGGER_CHANNEL_2_LEVEL). Now the OPO can lock coresonance again.

The PZT2 has total range of 20 V (-10 V to 10 V, it's ok to put -10 V on it). It's able to offload some DC bias from PZT1 (see Fig). The loop pushes the PZT1 voltage down while we increase the PZT2 to its maximum.

For the low FCGS power, we thought the problem was due to alignment. We've changed all ZMs and didn't find any improvements, so the alignement is fine. Then we tried walking the waveplates before the fiber coupler on SQZT0, which works well. It's now ~0.5 mW atperiscope downstreams after optimizing polarizations. The FCGS rejected PD is also calibrated (H1:SQZ-FC_REFL_REJECTED_DC_POWER) to the total FCGS REFL before any BS. The FCGS camera was also realigned to the current ZM offsets.

We received the new FCGS RF40 PD from Daniel and aligned the beam to its center.