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Entry  Thu Aug 9 02:12:13 2018, gautam, Update, COC, South East or West? 
    Reply  Wed Aug 15 12:15:24 2018, gautam, Update, COC, Macroscopic SRC length for SR tuning SRC_MCMC_shortTerm.pdfSRC_dists_shortTerm.pdf
Message ID: 14164     Entry time: Wed Aug 15 12:15:24 2018     In reply to: 14148
Author: gautam 
Type: Update 
Category: COC 
Subject: Macroscopic SRC length for SR tuning 

Summary:

It looks like we can have a stable SRC of length 4.044 m without getting any new mirrors, so this is an option to consider in the short-term.

Details:

  • The detailed calculations are in the git repo
  • The optical configuration is:
    • A single folding mirror approximately at the current SR3 location.
    • An SRM that is ~1.5m away from the above folding mirror. Which table the SRM goes on is still an open question, per the previous elog in this thread. 
  • The SRC length is chosen to be 4.044 m, which is what the modeling tells us we need for operating in the SR tuning instead of RSE.
  • Using this macroscopic length, I found that we could use a single folding mirror in the SRC, and that the existing (convex) G&H folding mirrors, which have a curvature of -700m, happily combine with our existing SRM (concave with a curvature of 142m) to give reasonable TMS and mode-matching to the arm cavity.
  • The existing SRM transmission of 10% may not be optimal but Kevin's calculations say we should still be able to see some squeezing (~0.8 dB) with this SRM.
  • Attachment #1 - corner plot of the distribution of TMS for the vertical and horizontal modes, as well as the mode-matching (averaged between the two modes) between the SRC and arm cavity.
  • Attachment #2 - histograms of the distributions of RoCs and lengths used to generate Attachment #1. The distributions were drawn from i.i.d Gaussian pdfs.

gautam 245pm: Koji pointed out that the G&H mirrors are coated for normal incidence, but looking at the measurement, it looks like the optic has T~75ppm at 45 degree incidence, which is maybe still okay. Alternatively, we could use the -600m SR3 as the single folding mirror in the SRC, at the expense of slightly reduced mode-matching between the arm cavity and SRC.

Attachment 1: SRC_MCMC_shortTerm.pdf  367 kB  Uploaded Wed Aug 15 13:24:48 2018  | Hide | Hide all
SRC_MCMC_shortTerm.pdf
Attachment 2: SRC_dists_shortTerm.pdf  198 kB  Uploaded Wed Aug 15 13:24:58 2018  | Hide | Hide all
SRC_dists_shortTerm.pdf
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