Ushiba, Tanaka

## Abstract

We suceeded in locking PRFPMI with DC readout when IFO input power was 10 W for the first time. During the trial, we found that OMC LSC could not lock with guardian maybe because the OMC input power (or IFO output power toward OMC?) seems to fluctuate largely when the IFO input power was 10 W. Therefore, we locked OMC manually. After OMC locked, The processes above the handover from TRAS to OMC DC could succeed by the guardian.

During the trial, we encounted the lock loss when OMC locked only once but the OMC PD seems to be fine after the lock loss maybe thanks to the protection. (Ushiba-san will report the detail)

I have not implemented the DC lock with 10 W input in the guardian because we need to make OMC LSC lock acquisition more robust. And I have not see the sensitivity curve carefully (because today was already too late to stay here)...

Anyway, we can perform the commissioning with 10 W PRFPMI from tomorrow.

I keep the IFO tonight. If the IFO lost the lock and the PD was not broken by the lock loss, PRFPMI DC lock restored with 1.2 W input automatically.

## What we did

• We decreased the DARM offset value by sqrt(1.2W/10 W) to keep the same IFO output power with TEM00 as 1.2 W input by modifiing this value in the ENGAGE_DARM_OFFSET state of the LSC_LOCK guardian.
• we modified the LSC_LOCK guardian to pass the INCREASING_LAS_POWER after PRFPMI_RF_LOCKED and before ENGAGE_DARM_OFFSET. This time, we leave the path which is connected from PRFPMI_RF_LOCKED to ENGAGE_DARM_OFFSET directly to be able to switch the 1.2 W input and the 10 W input if you lock the PRFPMI with the guardian. And If the IFO lost the lock and the PD was not broken by the lock loss, PRFPMI DC lock restored with 1.2 W input automatically.
• We engaged the DARM offset with the guardian.
• We tried to lock OMC but the OMC guardian could not succeeded in locking OMC. The guardian found TEM00 and triggered but the saturation occured soon and TEM00 resonance went away. We tried to reduce CLK_GAIN from 30000 to 5000, then the loop kept TEM00 resonance for a while.  Then, I turned on the filters and reduced CLK_GAIN to 500 after turning off the filters manually to engage the LOW_BANDWIDTH state. After that, I measured the OLTF of OMC LSC. Fig.1 shows the result. Red lines are the current TFs. During the measurement, the OMC lock often lost and restored. However, the OLTF seems to be the same as the IFO input was 1.2 W although the coherence seems too bad. This indicates the OMC input power (or IFO output power toward OMC?) seems to fluctuate largely when the IFO input power was 10 W.
• During the OMC lock trial, we encounted the lock loss when OMC locked only once but the OMC PD seems to be fine after the lock loss maybe thanks to the protection. (Ushiba-san will report the detail later)
• After that, I tried to hand over from TRAS to OMC DC and it was succeeded. I also requested LSC_LOCK to go to the OBSERVATION_WITHOUT_LINES state and it was succeeded.
• I measured the OLTFs of 4 DoF LSCs (DARM, PRCL, MICH, CARM) in this state. Fig. 2,3,4,5 shows the DARM, PRCL, MICH and CARM OLTFs, respectively. PRCL, MICH and CARM seem to be almost fine. DARM seems to be different from the reference but the reference seems too old and the boost filter was added the DARM filters recently. So we check it tomorrrow.
• The lock seems to be stable and the lock keeps more than 1 hours (fig.6). I left the IFO in this state tonight. If the IFO lost the lock and the PD was not broken by the lock loss, PRFPMI DC lock restored with 1.2 W input automatically.

## Next

• OMC lock automatically with guardian
• implement PRFPMI DC lock with 10 input in the guardain
• tune feedforward?
• 10 W commissioning