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Entry  Fri Apr 10 17:05:45 2015, ericq, Update, LSC, Relative ETM calibration (Rough MC2 calibration) quickCal.png
    Reply  Fri Apr 10 18:39:39 2015, ericq, Update, LSC, Relative ETM calibration (Rough MC2 calibration) betterCal.png
       Reply  Mon Apr 13 19:34:02 2015, ericq, Update, IOO, Modulation Frequency Tuned to IMC Length fMod_tuning.pdf
Message ID: 11216     Entry time: Mon Apr 13 19:34:02 2015     In reply to: 11215
Author: ericq 
Type: Update 
Category: IOO 
Subject: Modulation Frequency Tuned to IMC Length 

I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit. 


In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands. 

The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.

This implies a IMC round trip length of 27.090800m +- 2um.

Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency. 

 

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