40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
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: 2616     Entry time: Thu Aug 25 19:38:01 2022     In reply to: 2614
Author: Anchal 
Type: Summary 
Category: NoiseBudget 
Subject: Birefringence noise in thermo-optic noise 

 

Quote:

The obvious go to measurment here would be two-lasers-one-cavity to measure the residual between the two polarisaiton modes of one of the cavities. Is the experiment in a state where this could be done easily?

Not easily, but it is doable if we resurrect the south path only. I estimate ~1 month of work for that if things go fine.

Quote:
 

If I recall correctly Tara had this set up with an optical circulator on the input side which Antonio and I switched to linear polarisasion with Faraday isolator.  The mode splitting of the AlGaAs coatings would take care of only selecting one polarisation mode, but is it posisble that the latter measurments sampled a different polarisation to the original thermo-optic measurment? Just a thought.

With circularly polarized light, Tara could be addressing any of the two possible resonances, with only effect of suffering in modematching with the cavity. So it should be a 50/50 chance that they measured it in a different polarization. However, the nature of thermal photoelastic measurement is same in both polarizations. The photoelastic tensor for GaAs (cubic symmetry), in theroy, does not create birefringence, or afect different polarizations differently. The source of birefringence in these coatings is not known.

 

ELOG V3.1.3-