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Message ID: 1097
Entry time: Tue Oct 28 11:10:18 2008
In reply to: 830
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.