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Entry  Tue Mar 10 19:59:09 2020, Yehonathan, Update, Loss Measurement, Arm transfer function measurement YArmFrequencyResponse.pdf
    Reply  Thu Mar 12 10:43:50 2020, rana, Update, Loss Measurement, Arm transfer function measurement 
       Reply  Mon Mar 16 15:23:03 2020, Yehonathan, Update, Loss Measurement, Arm transfer function measurement Cross_calibration_setup.jpgPDA520overPDA255_Response.pdfYArmFrequencyResponse.pdf
          Reply  Sat Apr 18 14:57:44 2020, Yehonathan, Update, Loss Measurement, Arm transfer function measurement 
Message ID: 15277     Entry time: Mon Mar 16 15:23:03 2020     In reply to: 15269     Reply to this: 15307
Author: Yehonathan 
Type: Update 
Category: Loss Measurement 
Subject: Arm transfer function measurement 

I measured the cross-calibration of the two PDs on the PSL table.

I used the existing flip mounted BS that routes the beam into a PDA255, the same as in the IMC transmission.

I placed a PDA520, the same as the one measuring TRY_OUT on the ETMY table,  on the transmission of the BS (Attachment 1).

I used the SR785 to measure the frequency response of PDA520 with reference to PDA255 (Attachment 2). Indeed, calibration is quite significant.

I calibrated the Y arm frequency response measurement.

However, the data seem to fit well to 1/sqrt(f^2+fp^2) - electric field response - but not to 1/(f^2+fp^2) - intensity response. (Attachment 3).

Also, the extracted fp is 3.8KHz (Finesse ~ 500) in the good fit -> too small.

When I did this measurement for the IMC in the past I fitted the response to 1/sqrt(f^2+fp^2) by mistake but I didn't notice it because I got a pole frequency that was consistent with ringdown measurements.

I also cross calibrated the PDs participating in the IMC measurement but found that the calibration amounted for distortions no bigger than 1db.

Attachment 1: Cross_calibration_setup.jpg  5.852 MB  Uploaded Mon Mar 16 16:33:41 2020  | Show | Hide all | Show all
Attachment 2: PDA520overPDA255_Response.pdf  18 kB  Uploaded Mon Mar 16 16:38:20 2020  | Hide | Hide all | Show all
Attachment 3: YArmFrequencyResponse.pdf  32 kB  Uploaded Mon Mar 16 16:42:50 2020  | Hide | Hide all | Show all
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