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Entry  Mon Dec 14 19:33:04 2009, Alberto, Update, General, Arm Cavity Poles measured again after cleaning the optics last week XarmTF01_fit.pdfYarmTF01_fit.pdfArmCavityFinesseMeasurment.tar.gz
    Reply  Tue Dec 15 05:29:31 2009, Alberto, Update, General, Arm Cavity Poles measured again after cleaning the optics last week 
Message ID: 2415     Entry time: Mon Dec 14 19:33:04 2009     Reply to this: 2418
Author: Alberto 
Type: Update 
Category: General 
Subject: Arm Cavity Poles measured again after cleaning the optics last week 

Last week we vented and we cleaned the main optics of the arm cavities.

I measured the frequency of the cavity poles for both the arm cavities to see how they changed (see previous elog entry 2226). These the results:

fp_X = 1616 +/- 14 Hz

fp_Y = 1590 +/- 4 Hz

The error is the statistical error that I got with the Matlab NonLinearLeastSquare fitting function.
 
I calculated the cavity pole frequencies by measuring the transfer function between a photodiode located at the end of the arms (either X or Y) and another photodiode placed after the mode cleaner. Both diodes where Thorlabs PDA255.
(Last time, I had measured that the pair of diode had a flat calibration).
 
With the SR785 I measured the transfer function by exciting the OMC_ISS_EXC input cable.
For both arms I set to 1V the excitation amplitude. I repeated the measurements for different excitation amplitudes without observing any changes.
I then fitted the data with the NonLinearLeastSquare function of matlab. The script I wrote to do that is attached to this entry in a compressed file.
The files also contains the PDF with the output plots and the data from both set of measurements performed before and after the cleaning.
The data is commented in a file called measurements.log.
 
In the end I disabled again the test switch on the ISS MEDM screen.
I disconnected the excitation cable from the OMC_ISS_EXC input cable.
I removed the photodiode that measured the Mode Cleaner transmission from the PSL clearing the way for the beam to get back to its path to the RFAM photodiode.
Attachment 1: XarmTF01_fit.pdf  8 kB  | Hide | Hide all
XarmTF01_fit.pdf
Attachment 2: YarmTF01_fit.pdf  8 kB  | Hide | Hide all
YarmTF01_fit.pdf
Attachment 3: ArmCavityFinesseMeasurment.tar.gz  848 kB
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