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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: 1097     Entry time: Tue Oct 28 11:10:18 2008     In reply to: 830
Author: Alberto 
Type: Update 
Category: LSC 
Subject: Higher Order Mode resonances in the X 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.

I plugged the measures of the length of the X arm and radius of curvature of ETMX I made in to John's code to estimate the position of the resonances of the HOM for the sidebands in the X arm. Here's the resulting plot.
Attachment 1: HOM_resonances_Xarm.png  29 kB  | Hide | Hide all
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