Today, I did two things:

1. Modulation index for Green X lowered and gain of PDHX servo changed.
As the RF power applied to EOM for Green X had been known to be too much, a 30 dB attenuator was inserted between RF generator and EOM.
The gain of IN1 of PDHX servo was increased from -14dB to 14dB, then.
The motivation for this decrease of the modulation index was, to remove non-linear nasty noise in servos as reported in 7336.
Before this work ALS-PDHX_SLOW_DAQ_OUT was covered by this noise in a broad frequency range, but now it has been removed.
See this figure.

2. Test measurement for out-of-loop stablitiy of ALS
As mentioned in 7425, our previous measurements were covered by some noises at some region.
So today, I tested the method of the out-of-loop stablity measurement.
The method is:
- main laser is locked to X arm
- green laser is also loced to X arm
- the feedback signal of the green lock is ampified by a factor of 100 and then sent to ADC.
As the following figure shows (red: with amp., blue: without amp), the new witness channel is more sensitive to the previous one blow 10 Hz.
I could not do the actual measurements since the IFO was not happy due to the earthquake and temerature drift due to turning off air filters.