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Entry  Tue Apr 30 01:15:26 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
    Reply  Thu May 2 03:03:48 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
       Reply  Thu May 2 23:40:46 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 6x
          Reply  Mon May 6 03:11:44 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO RefCav_AlGaAs_TOnoise.png
             Reply  Mon May 6 17:08:25 2013, Matt A., Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
             Reply  Tue May 14 02:06:15 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
                Reply  Wed May 15 20:07:12 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO TO_compare_cap.pngTO_compare_cap.fig
                   Reply  Tue May 21 01:06:43 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
                      Reply  Wed May 22 00:04:48 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
                         Reply  Fri May 24 04:04:58 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 
                            Reply  Fri May 24 23:57:27 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO 6x
                               Reply  Wed Jun 5 22:25:28 2013, tara, Notes, NoiseBudget, TO calculation review 
                         Reply  Thu Jun 6 22:28:46 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO eighth.png
                            Reply  Tue Jun 11 00:45:48 2013, tara, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity sk2009nb.pngsk2009nb.fig
                               Reply  Tue Jun 11 16:46:52 2013, tara, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity getCoatBrownian2.m.zip
                               Reply  Wed Jun 12 01:34:27 2013, Koji, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity 
                                  Reply  Wed Jun 12 14:32:22 2013, not Koji, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity 
                                     Reply  Wed Jun 12 14:49:47 2013, Koji, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity 
                                        Reply  Fri Jun 14 02:36:22 2013, tara, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity 
                                           Reply  Tue Jun 18 11:53:17 2013, tara, Notes, NoiseBudget, noisebudget for 8" SiO2/Ta2O5 cavity spacer_br_8_edge.png
                            Reply  Mon Jul 15 10:55:40 2013, tara, Notes, NoiseBudget, AlAs/GaAs layer structure optimized for TO alGaAsnb.pngalGaAsnb.fig
Message ID: 1163     Entry time: Tue Apr 30 01:15:26 2013     Reply to this: 1168
Author: tara 
Type: Notes 
Category: NoiseBudget 
Subject: AlAs/GaAs layer structure optimized for TO 

I'm computing  coating Brownian and thermo optic noise (TO)  in AlGaAs coatings using GWINC code to compare it with the result reported by G Cole etal. Brownian noise from my result is similar to theirs, but TO noise is still not correct.  I'm working on it.

==Background==

We have talked about what kind optimizations should we go for AlGaAs coatings in order to minimize TO noise. There are two choices for us to consider

  1. using the layer structure as proposed in T1200003, or
  2.  adding a half wavelength cap on top of the quarter wave stack coatings as suggested by the authors.

Since the second option is more desirable in terms of manufacturing because of its simplicity, I decided to check if it really can  bring TO noise below coating Brownian noise. If it is true, we can use it for our mirrors.

 ==calculation==

  • I use GWINC code for TO noise and brownian noise calculations to verify the result if they are agree or not.
  • Materials parameters used in the calculation are taken from the paper. But most of the coatings material properties of an individual layer of AlxGa1-xAs are not provided. There are only the average values of thermal expansion, heat capacity, thermal conductivity, dn/dT.  There are refractive indices (nh/nl = 3.48/2.977) and layer structure (81 layers, starts with nh, ends with nh). So, as a start, the values for high index material and low index material are the same as the averaged values.

==result==

  • My Coating thermal noise level is 8.4*10^-35 m^2/Hz while their result is 9.8 *10^-35 m^2/Hz, @ 1Hz. This is not very bad, since there are some differences in the formulas between GWINC and their calcualtion.
  • However, my TO is off the roof, almost 2 orders of magnitude above their result. I'm checking if it is because of the code is wrong(typo in the parameters) or the fact that I used all the averaged values.

(I'll add more details about the calculations later)

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