[Nakano,Kitazawa]

Loop closed!!(without boost) then Servo Gain is MAX.

Laser power = 3W output from the fiber amp.
PD output (in-loop) : 3.0 V
PD output(out-of-loop) : 2.6V

In this time, free run of laser output and PMC output is left-hand picture. RIN(Free run, In-loop and Out-of-loop) is shown in the right-hand picture.Both In-loop and out-of-loop noise are suppressed to about 10^-6/rHZ

Issue:

Gain is too low.
We would like to raise of UGF to 75kHz(considering the phase margin).
In this condition, boost cannot be engaged.
Since we need 30dB more, we should go up PD output voltage to 9V(=+10dB) and increase servo gain by 20 dB.