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Message ID: 3023     Entry time: Tue Jun 1 06:30:38 2010
Author: Koji 
Type: Configuration 
Category: 40m Upgrading 
Subject: effect of the arm length  

I checked the effect of the arm length to the reflectance of the f2(=5*f1) sidebands.

Conclusion: If we choose L_arm = 38.4 [m], it looks sufficiently being away from the resonance
We may want to incorporate small change of the recycling cavity lengths so that we can compensate the phase deviation from -180deg.

f1 of 11.065399MHz is assumed. The carrier is assumed to be locked at the resonance.

Attachment 1: (Left) Amplitude reflectance of the arm cavity at f2 a a function of L_arm. (Right) Phase
Horizontal axis: Arm length in meter, Vertical Magnitude and Phase of the reflectance

At L=37.93 [m], f2 sidebands become resonant to the arm cavity. Otherwise, the beam will not be resonant.

Attachment 2: close-up at around 5 f1 frequency.
The phase deviation from the true anti resonance is ~0.7deg. This can be compensated by both PRC and SRC lengths.

Attachment 1: arm_cavity1.png  18 kB  Uploaded Tue Jun 1 15:57:48 2010  | Hide | Hide all
Attachment 2: arm_cavity2.png  23 kB  Uploaded Tue Jun 1 15:57:55 2010  | Hide | Hide all
Attachment 3: arm_cavity.nb.zip  154 kB  Uploaded Tue Jun 1 15:58:03 2010
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