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Entry  Tue Aug 12 21:38:19 2008, John, Update, LSC, Accidental higher order mode resonances in the arms HOMresonances.pngHOMarms2.m
    Reply  Tue Oct 28 11:10:18 2008, Alberto, Update, LSC, Higher Order Mode resonances in the X arms HOM_resonances_Xarm.png
Message ID: 830     Entry time: Tue Aug 12 21:38:19 2008     Reply to this: 1097  
Author: John 
Type: Update 
Category: LSC 
Subject: Accidental higher order mode resonances in the arms 
Recently we had been having some trouble locking the full IFO in the spring configuration (SRC on +166).
It was thought that an accidental higher order mode resonance in the arms may have been causing problems.

I previously calculated the locations of the resonances using rough arm cavity parameters(Elog #690). Thanks to Koji
and Alberto I have been able to update this work with measured arm length and g factors for the y arm (Elog #801,#802).
I have also included the splitting of the modes caused by the astigmatic ETM. Code is attached.

I don't see any evidence of +166MHz resonances in the y arm.

In the attached plot different colours denote different frequencies +33, -33, +166, -166 & CR.
The numbers above each line are the mn of TEMmn.
Solid black line is the carrier resonance.
Attachment 1: HOMresonances.png  25 kB  | Hide | Hide all
Attachment 2: HOMarms2.m  4 kB  | Hide | Hide all
%Check for accidental resonances of HOM in the arms (maybe due to
%sidebands). At the moment there is only data for the y arm.

clear all
close all

%Stuff one might change often
modeorder = 0:5;          % Look for TEMmn modes where m,n run over modeorder
... 157 more lines ...
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