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Message ID: 9231     Entry time: Thu Oct 10 11:46:43 2013
Author: Jenne 
Type: Update 
Category: SUS 
Subject: ITMY OpLev Noise 

For my work designing a cost function, so that I can try out new feedback servo designs on the oplevs, I wanted to know what the dark noise of an oplev is.  Since the pitch and yaw channels are divided by the sum channel, when the laser is off, the noise in the pitch and yaw channels looks much higher than it really is.  So, I collected some data from the 4 individual quadrants of the ITMY oplev, when the laser was on (but damping was off), and when the laser was off.  I used the values of the oplev input matrix to re-create the non-normalized pitch and yaw signals.  What I see is that we have some kind of real signal below 1 kHz, but we're hitting the noise at around 1 kHz.  So, we definitely don't want to use oplev error signal information above 1 kHz when designing new servos.

The last word in the title is "off".  OSEM damping was on, but the oplev damping was off.  These are uncalibrated, because the calibrations that we have to go from counts to microradians are for the normalized signals. 

ITMY_OpLev_Noise.png

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