I did some more stuff for the Y arm ALS and updated the noise budget:

After the works, the rms displacement improved a little bit, so it is now at 24 pm in rms.

Though, it turned out that the MFD's ADC is now limiting the noise in a frequency band of 200 mHz - 5 Hz.

So tonight I will increase the gain of the whitening filter to push down the ADC noise more.

(What I did)

 + added the DAC noise and comparator noise based on measurements.

 + redesigned the servo filter shape to suppress the seismic noise below 10 Hz.

 The attached plot below shows the newly designed open loop transfer function together with the old one for a comparison.

UGF is at 120 Hz and the phase margin is about 27 deg.

• FM7 = resonant gain (17)
• FM6 = resonant gain (3)
• FM5 = zero(1) * pole(500)
• FM4 = pole(1) * zero(40.) * 40.
• FM3 = pole(1) * zero(40.) * 40.
• FM2 = pole(0.001)*zero(1)*1000.