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Entry  Tue Mar 13 19:14:40 2012, kiwamu, Update, LSC, Noise estimatino in the REFL33Q as a MICH sensor NB_REFL33.png
    Reply  Wed Mar 14 13:16:50 2012, kiwamu, Update, LSC, A correction on Noise estimatino in the REFL33Q 
Message ID: 6414     Entry time: Wed Mar 14 13:16:50 2012     In reply to: 6407
Author: kiwamu 
Type: Update 
Category: LSC 
Subject: A correction on Noise estimatino in the REFL33Q 

A correction on the previous elog about the REFL33Q noise:

 Rana pointed out that the whitening filter's input referred noise should not be such high (I have estimated it to be at 54 nV/sqrtHz).
In fact the measurement was done in a condition where no laser is on the photo diode by closing the mechanical shutter at the PSL table.
Therefore the noise I called "whitening filter input referred noise" includes the voltage noise from the RFPD and it could have such a noise level.
So the noise curve drawn in the plot should be called "whitening filter + RFPD electronics noise".

Quote from #6407

A feasibility study of the REFL33Q as a MICH sensor was coarsely performed from the point view of the noise performance.

  • Whitening filter input referred noise
    • I assumed that it is flat with a level of 54 nV/sqrtHz based on a rough measurement by looking at the spectrum of the LSC input signals.
    • The contribution was estimated by applying some gain corrections from the conversion efficiency of the demod board, transimpedance gain, responsivity and the optical gain.
    • This noise is currently the limiting factor over a frequency range from DC to 1 kHz.

 

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