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Entry  Mon Sep 12 01:21:14 2011, tara, DailyProgress, BEAT, beat layout beat_2011_09_12.png
    Reply  Tue Sep 13 20:54:11 2011, tara, DailyProgress, BEAT, beat layout 
       Reply  Wed Sep 14 19:17:19 2011, frank, paul, tara, DailyProgress, BEAT, beat layout beat_2011_09_14.pngSnapshot_2011-09-14_19-39-37.png
          Reply  Tue Sep 20 00:12:46 2011, rana, DailyProgress, BEAT, seismic noise coupling 
             Reply  Tue Sep 20 01:49:44 2011, Frank, DailyProgress, BEAT, seismic noise coupling 
                Reply  Wed Sep 21 01:39:11 2011, tara, DailyProgress, BEAT, seismic noise coupling beat_2011_09_20_m.pngbeat_2011_09_20_m.fig
Message ID: 678     Entry time: Wed Sep 14 19:17:19 2011     In reply to: 677     Reply to this: 687
Author: frank, paul, tara 
Type: DailyProgress 
Category: BEAT 
Subject: beat layout 

 Beat signal from double cavities in the same chamber was measured. At DC to 100Hz, it seems to be dominated by seismic. Above 100 Hz, the frequency's laser noise is the limiting source. The setup has yet to be optimized. This is for a quick check to see how beat signal changes with the new seismic isolation setup.

      I measured beat signal after Paul and Frank locked ACAV. At frequency above 100 Hz, beat signal changes with RCAV's gain setup. Error signal from RCAV's mixer out matches the shape of the beat signal ( I did not do the  calibration with error signal slope, just observed the displays on SR785). However, at low frequency (DC - 100 Hz), the beat signal does not change with anything, RCAV gain, ACAV gain, PLL gain, so I'm quite certain that it's the real signal we see here.

beat_2011_09_14.png

Tuning range on PLL loop was 10kHz, the calibration is 7kHz/V. A peak close to 7 Hz might come from the beam line transverse mode of the stack.

At DC - 10 Hz, the noise is lower than before. This might be the result from common mode suppression. However, the two spacers are not identical. They have significantly different holes' sizes. This may explain why the seismic cancellation is not that good at higher frequency.

Snapshot_2011-09-14_19-39-37.png

We might have to suspend the whole vacuum chamber to win against seismic.

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