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Entry  Wed Sep 7 22:41:44 2011, frank,tara, DailyProgress, , Two cavities are in the same chamber P1040900.JPG
    Reply  Thu Sep 8 20:53:17 2011, tara, DailyProgress, RefCav, frequency difference 
       Reply  Fri Sep 9 01:45:40 2011, Frank, DailyProgress, RefCav, frequency difference 
       Reply  Fri Sep 9 01:53:21 2011, Frank, DailyProgress, RefCav, frequency difference 
       Reply  Fri Sep 9 22:53:32 2011, frank, tara, DailyProgress, RefCav, frequency difference 
    Reply  Mon Oct 3 23:54:19 2011, frank, tara, DailyProgress, , re mode matching 
       Reply  Tue Oct 4 23:20:57 2011, frank, tara, DailyProgress, , re mode matching 
Message ID: 669     Entry time: Thu Sep 8 20:53:17 2011     In reply to: 667     Reply to this: 671   672   673
Author: tara 
Type: DailyProgress 
Category: RefCav 
Subject: frequency difference 

 I aligned the beam to ACAV and RCAV and measured the frequency difference between the two cavities to be 289 MHz.

 

I used SLOWDC for calibration, the beam resonates in ACAV and RCAV at

 

 DClevel                                  RCAV                 ACAV

     1st resonance       -0.0520 [V]                0.0088  [V]

      2nd resonance       0.1046                      0.1661

     dV                           0.1566                        0.1573

 

 For a quick calculation, I used nominal FSR = 737 MHz. The calibration is then FSR/dV = 4700 MHz/V.

The frequency different between the two cavities give (0.1661 - 0.1048)*4700MHz/V = 289 MHz.

(I think the frequency might be too high for the beat PD, we may need to have thermal control before we can measure the beat)

 use df/f = dL/L, the differential length between the two cavities is   dL =  df * L * lambda / c ~ 0.2 micron.

So common mode suppression for thermo-elastic or cavity sagging due to seismic can be approximated to be ~ dL/L = 0.2 micron / 0.2 m =  1e-6.

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