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Entry  Mon Aug 22 20:18:21 2022, Anchal, Summary, NoiseBudget, Birefringence noise in thermo-optic noise CTN_Thermo-Optic_Noise_Study.pdf
    Reply  Tue Aug 23 19:56:21 2022, Anchal, Summary, NoiseBudget, Birefringence noise in thermo-optic noise CTN_Thermo-Optic_Noise_Study.pdf
       Reply  Tue Aug 23 22:04:24 2022, awade, Summary, NoiseBudget, Birefringence noise in thermo-optic noise 
          Reply  Thu Aug 25 19:38:01 2022, Anchal, Summary, NoiseBudget, Birefringence noise in thermo-optic noise 
       Reply  Thu Aug 25 19:19:27 2022, Anchal, Summary, NoiseBudget, Looking at the measured and estimated photothermal transfer functions CTN_Photothermal_TF_with_TPE.pdfCTN_Thermo-Optic_Noise_Study.pdf
          Reply  Fri Aug 26 15:56:38 2022, Anchal, Summary, NoiseBudget, Checking with Martin Fejer's calculations CTN_Photothermal_TF_with_TPE.pdfCTN_Thermo-Optic_Noise_Study.pdf
Message ID: 2615     Entry time: Thu Aug 25 19:19:27 2022     In reply to: 2613     Reply to this: 2617
Author: Anchal 
Type: Summary 
Category: NoiseBudget 
Subject: Looking at the measured and estimated photothermal transfer functions 

The photothermal transfer function measurement made back in 2014 showed some cancellation of thermo-optic noise, but there were some irregularities with the modelled transfer function even back then. Here in attachment 1, I have plotted the measured photothermal transfer function, along with the estimated transfer function with and without adding a term for thermal photoelastic (TPE) channel.


Notes:

  • The estimated transfer function without TPE (as was estimated back then) does match well with the measured transfer function on the south cavity below 200 Hz.
  • However, the north cavity measurement did not match well.
  • The estimated transfer function with TPE (green) is in between south and north measurements at least in magnitude above 200 Hz.
  • However, the phase of estimated transfer functions (with or without TPE) do not match well with any of the measurements. This phase discrepancy is worrisome.
  • Looking at these estimated transfer functions and measured transfer functions, which model do you think explains the measured data better?

Updated noise budget:

I was wondering if photothermal noise would get amplified due to the TPE effect. We were not using a measured photothermal transfer function in our noise budget for this noise contribution and relied on a theoretical model instead. For comparison, I added noise traces for three cases, Estimated photothermal noise with and without PTE, and photothermal noise using measured TF. In all these cases though, the ISS in the experiment suppressed RIN enough that photothermal noise did not matter to beatnote frequency noise.

Attachment 1: CTN_Photothermal_TF_with_TPE.pdf  36 kB  Uploaded Thu Aug 25 20:19:37 2022  | Hide | Hide all
CTN_Photothermal_TF_with_TPE.pdf
Attachment 2: CTN_Thermo-Optic_Noise_Study.pdf  48 kB  Uploaded Thu Aug 25 20:31:24 2022  | Hide | Hide all
CTN_Thermo-Optic_Noise_Study.pdf
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