The new noisebudget code follows Hong et al . PRD 87, 082001 (2013) calculations to calculate Coating Brownian noise. This calculation uses different loss angles for bulk and shear strain. In fact, the calculation uses different loss angles for each layer as well if known. The closest reported values I could find are from Penn et al. JOSA B 36, 4, pp C15-C21 (2019). They used mechanical ringdown measurements of large disks and COMSOL modeling to estimate the bulk and shear loss angles.
I used these values and compared the change in the estimate of coating Brownian noise contribution. Attached is the result.
~~If the loss angles values reported by Penn et al. are correct, then our Coating Brownian noise would actually be buried beneath all other noise contributions. So I'm not sure what is correct, what is not?~~ Is my understanding of this wrong somewhere?
The old calculations were described in CTN:2250.
I would like some guidance on this.
Edit Wed Aug 28 10:49:45 2019 anchal:
I did a mistake in the plot earlier. The new data was in PSD, not ASD, so it needed to be square-rooted before comparing with the old data. I've updated the plot now.
It seems like the induction of new values and new method changed the effective coating loss angle (used in the previous calculations). If Penn et al. values are correct the expected Coating Brownian noise contribution has actually increased by about a factor of 5. However, I'm not sure where the previously used effecting coating loss angle value of (2.41 +/- 0.2)e-5 came from. Complete noisebudget is coming soon. |