[Kenta, Masayuki]

Now, all of the suspension has strong OL loop, and the ALS DARM does not have any difference from the privious oplev control.

As shown in the second spectra, the RMS is below 10 nrad. The YAW motion is still large below 1 Hz. This is because the TM oplev is not used for the YAW control, but only MN oplev. We should use the sensor which monitoring TM motion to reduce the yaw motion below 1 Hz, so we are trying to use GR QPD to reduce these frequencies.

BTW, above 3 Hz, the ALS DARM signal seems to be limitted by the GR RFPD dark noise used for GR-PDH loop. If we can increase the modulation index, the ALS performance would be improved.