Message ID: 1170
Entry time: Mon May 6 03:11:44 2013
In reply to: 1169
Reply to this: 1171 1176

Author:

tara

Type:

Notes

Category:

NoiseBudget

Subject:

AlAs/GaAs layer structure optimized for TO

I checked the calculation for TO noise in Cole etal people and found a few problems that I didn't understand.

In the paper, they have two solutions for TO-noise, at low and high frequency. The solution for high frequency is similar to that in Evan etal paper, but I'm not sure where the solution for low frequency are from. I don't see this kind of calculation in Evans etal paper.

I repeated and plotted the TO noise calculation as used in Cole etal's paper. The TO noise plotted in their paper mostly came from the low frequency part.

Some parameters reported in the paper might not be accurate, for example their beam radius is 250 um. However, with their 35mm spacer, 1.0 m RoC mirrors, the spotradius on the mirror should be 212 um. I haven't checked how much their materials parameters and what I used in my codes differ.

For low frequency solution (solid blue line), with the materials parameter given in the paper, it is a factor of 1.5 higher than their result (I got 3e-3, they report ~2 e-3 around 1-10 Hz).

For high frequency solution (solid yellow line), with the materials parameters given in the paper, the result is about a factor of 10 higher than that from Gwinc code (dashed blue line). The formulas are the same, but I used different material parameters. The two lines should be close, but they are a factor of 10 apart, just because of the material parameters. We should really make sure that the numbers are correct. Before trying to do the optimization.

My GWINC code for TO calculation can be found here. (other modified functions are in /GwincDev/ ).The main code is plotTO_algaas.m. This code uses getCoatThermoOpticsAGS.m which calls out other other functions in /gwincdev/

getcoatTOposAGS.m (calculated effective alpha and beta in coatings.) This function uses getcoatLayers.m to generate the layer structure. The original one started with nL, I modified it to start with nH, and end with nH.

getcoatThickCorrAGS.m, which computes the correction factor (gamma TO).

getcoatavgAGS.m, this code compute the average material parameters in coatings.

in /coating/AlGaAs_Refcav, I created a database file for material parameters called algaasmodels.m.