Message ID: 1176
Entry time: Tue May 14 02:06:15 2013
In reply to: 1170
Reply to this: 1177

Author:

tara

Type:

Notes

Category:

NoiseBudget

Subject:

AlAs/GaAs layer structure optimized for TO

[matt,tara] We compared the TO result using GWINC, our results are similar (see PSL:1170). However, it still not agrees with result in Cole etal paper.

The result from GWINC and Cole etal's result are different in the following ways:

TO noise from GWINC is higher their result. This might be due to different values of the effective alpha, and effective beta in the calculation. We will check this next.

The calculated transmission for 81 layers is ~ 1.8 ppm, while they reported 10ppm. We are not sure what happen here.

Half wave cap solution for TO noise cancellation is not shown in GWINC.

Thermal fluctuation as observed by a Guassian beam, S^{dT}_{TO }= const x kBT^2/ r0^2 sqrt(kappa x heat cap x 2*pi*f) depends on substrate parameters in GWINC, but their result use coatings' parameters. With coatings parameters, the thermal fluctuation will be lower, thus lower TO noise. It means that our TO result should be larger by an order of magnitude. However the results are about the same. We think that the subsrate parameters should be used in the calculation, because thermal length in the coatings from dc up to 170kHz is smaller than the coatings thickness (~6 um).

The calculation in GWINC assumes adiabatic assumption. However, the assumption breaks down at 270 Hz for AlGaAs coatings, and 6 Hz in substrate. That explains why the TO noise in Cole paper is almost flat from DC to 100 Hz. Mike Martin's thesis explains the TO noise at all frequency, but I haven't yet quite understood all the equations.