40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  Coating Ring-down Measurement Lab elog  Not logged in ELOG logo
Message ID: 29     Entry time: Fri Jul 1 15:12:12 2016
Author: Gabriele 
Type: Electronics 
Category: Daily Progress 
Subject: QPD electronics noise 

 

I turned out that all the noise I was seeing in the QPD spectrum was due to ambient light. I covered the QPD with a box and switched off all the light. As shown in the following plot the noise is lower.

Considering that in the final setup we'll have a beam spot radius of 0.5mm, the sensitivity to beam motion on the QPD will be 23e6 V/m. The following plot shows the resulting beam motion sensitivity, if limited by electroninc noise:

It's at a level of 6e-15 m/rHz at all frequencies above 120 Hz.

ELOG V3.1.3-