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Message ID: 15322     Entry time: Fri May 8 14:27:25 2020
Author: Hang 
Type: Update 
Category: BHD 
Subject: New SRC gouy phase 

[Jon, Hang]

After updating the 40 m finesse file to incorporate the new SRC length (and the removal of SR2), we find that the current SRM radius curvature is fine. Thus a replacement of SRM is NOT required

Basically, the new one-way SRC gouy phase is 11.1 deg according to Finesse, which is very close to the previous value of 10.8 deg. Thus the transmode spacing should be essentially the same. 

In the first attached plot is the mode content calculated with Finesse. Here we have first offset DARM by 1m deg and misaligned the SRM by 10 urad. From the top to bottom we show the amplitude of the carrier fields, f1, and f2 sidebands, respectively. The red vertical line is the nominal operating point (thanks Koji for pointing out that we do signal recycling instead of extraction now). No direct co-resonance for the low-order TEM modes. (Note that the HOMs appeared to also have peaks at \phi_srm = 0. This is just because the 00 mode is resonant and thus the seed for the HOMs is greater. )

We can also consider a clean case without mode interactions in the second plot. Indeed we don't see co-resonances of high order modes. 

Attachment 1: mode_spec_finesse.pdf  161 kB  Uploaded Fri May 8 15:35:59 2020  | Hide | Hide all
Attachment 2: mode_spec_ideal.pdf  169 kB  Uploaded Fri May 8 15:36:14 2020  | Hide | Hide all
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