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Entry  Thu Sep 11 00:47:14 2014, Evan, DailyProgress, optic, South photothermal TF spt.pdfsouthPT.zipphotothermalTF.pdf
    Reply  Thu Sep 11 11:40:41 2014, Evan, DailyProgress, optic, South photothermal TF spt.pdfsouthPT.zipphotothermalTF.pdf
Message ID: 1511     Entry time: Thu Sep 11 00:47:14 2014     Reply to this: 1512
Author: Evan 
Type: DailyProgress 
Category: optic 
Subject: South photothermal TF 

I took a swept-sine measurement of the photothermal TF just as Tara and I did for the north cavity. To get a better measurement, I made some configuration changes:

  • I turned the power incident on the south cavity up to 8.5 mW by adjusting the post-laser HWP from 318° to 286°.
  • I placed an OD2.0 in front of the beat PD to prevent RF saturation.


  • The beat was at 13.8 MHz.
  • The PLL Marconi was on 50 kHz FM deviation, and the SR560 gain was 100 V/V.
  • South transmission PD was 460(5) mV dc.
  • South transmission power (directly out of vacuum chamber) was 2.20(5) mW dc.

The results are attached. I'm not sure why there's a discrepancy around 200 Hz between the two traces. Below 100 Hz the measurement looks relatively clean.

The light rejected out of the post-EOAM PBS is only 2 mW (compared with 9 mW transmitted), which makes me suspicious that the post-EOAM QWP is not rotated properly, or else the input polarization into the EOAM is wrong. We should check this before redoing this measurement.

As with the north cavity, I find that an absorption of 6 ppm is needed make the measured curve lie on top of the theory curve.

For the time being, I have left the input power at 8 mW in case we want to take this again tomorrow. There's currently a dump upstream of the PMC to block the beam.

Attachment 1: spt.pdf  71 kB  | Hide | Hide all
Attachment 2: southPT.zip  20 kB
Attachment 3: photothermalTF.pdf  104 kB  Uploaded Thu Sep 11 01:54:03 2014  | Hide | Hide all
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