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 Fri Feb 14 17:40:27 2020, anchal, DailyProgress, ISS, Installed ISS on both paths using SR560s Sat Feb 15 18:57:43 2020, rana, DailyProgress, ISS, Installed ISS on both paths using SR560s Thu Feb 20 17:42:23 2020, rana, DailyProgress, ISS, Installed New ISS on both paths using SR560s Sun Feb 23 18:19:32 2020, rana, DailyProgress, ISS, Installed New ISS on both paths using SR560s Fri Feb 28 14:00:11 2020, anchal, DailyProgress, ISS, Installed New ISS on both paths using SR560s - PROBLEM Sun Mar 1 16:34:31 2020, rana, DailyProgress, ISS, Installed New ISS on both paths using SR560s - PROBLEM Mon Mar 2 16:48:12 2020, anchal, DailyProgress, ISS, Follow-up, porbalem stopped happening, OLTF plot.
Message ID: 2542     Entry time: Thu Feb 20 17:42:23 2020     In reply to: 2539     Reply to this: 2544
 Author: rana Type: DailyProgress Category: ISS Subject: Installed New ISS on both paths using SR560s

I've installed new ISS consisting of one SR560 per path.

### ISS SR560 Details:

Path Input Coupling Invert High Pass Roll off (dB/octave) High Pass Corner (Hz) Low Pass Roll off (dB/octave) Low Pass Corner (Hz) Gain Mode Gain Output Impedance (Ohms)
North AC No 6 300 6 300 Low Noise 5x103 600
South AC Yes 6 300 6 300 Low Noise 1x104 600

### Measurements:

• I took transfer function by exciting at port B and using mode A-B on the SR560.
• The transfer function was measured as Actuation Signal (output of SR560) over Error Signal (input to SR560).
• This transfer function should be equal to open-loop gain over the SR560 transfer function.
• So, I took another measurement of the transfer function of SR560 itself not connected to the loop.
• This gave me total open-loop transfer function.
• I used $\frac{\pi}{2V_{\pi}}$ as the transfer function of EOAM in units of relative intensity change per V (1/V).
• I used the coupling factor (See CTN:2528) and DC power level of the laser after transmission to get the detector transfer function in units of V.
• Using the above, I calculated the plant transfer function for each path and then used that to calculate the closed-loop transfer function.
• To compare, I also calculated noise suppression before and after switching on ISS.
• These two separate methods match very well. At 300 Hz, intensity noise is suppressed by 40 dB.
• There is no other witness detector after transmission to use as an out-of-loop photodiode, neither is there any space to put a new one.
• There is oscillation happening at UGF  fo around 40 kHz in both paths. I can work on it if this looks like a problem in the final beatnote or if it seems to saturate FSS loops. Currently, I saw nothing alarming.

Data

 Attachment 1: ISS_New_Analysis.pdf  99 kB
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