[Miyakawa, Ushiba, Nakano]

The IMC CMS settings have been changed for the higher power operation. The nominal power is 3.1W, i.e. 16degrees of the PSL HWP rotation stage. 

For the stable operation, the CMS gain is 10dB and 22dB for IN1 and FAST gain. The measured OLG and the cross-loop gain are attached, showing the UGF of 110kHz cross-over frequency between the PZT and EOM loop of 14kHz with the phase margin of >30degs.

We checked the IMC can be operated with the highest power output from the current PSL (~9W) just by rotating the HWP in the PSL. 

We should note that we cannot acquire the IMC lock with the highest PSL power due to the PD saturation. The linear range of the PDH error signal got too small to catch the resonance with the highest power. If we really want to lock with the higher power, the IMC REFL PD power needs to be reduced, although the current procedure is stable enough.