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Message ID: 1150     Entry time: Mon Nov 8 17:18:14 2010
Author: Zach 
Type: Laser 
Category: GYRO 
Subject: electronic noise contributions 

 Below is a plot of one particular gyro signal channel along with various electronics noise contributions to the gyro signal in general. The traces are:

  1. The secondary error signal with the secondary loop open (but the primary closed, so that the error signal is kept within the linear regime). This gives a linear output proportional to the measured frequency mismatch between the two cavity directions, and is thus a form of gyro signal. Typically, we would lock the second loop and read this out at the feedback point, but it is useful to do this way as an intermediate measure when trying to characterize the loops.
  2. Noise at the INMON of the primary box with the laser off, divided by 42 to obtain the level at the true servo input.
  3. Same as (2), but for the secondary loop.
  4. Noise at the INMON of the primary box with a 50-ohm terminator in place of the PD (i.e. noise in the demod electronics).
  5. Output noise of the primary PDH box with the input terminated, divided by the estimated analytical transfer function of the box with G = 0.5 (as when the noise spectrum was measured).

All of these signals were then divided by the cavity response in [V/Hz]---which are all the same except for in (3)---and then multiplied by (lambda P / 4A) to obtain spectra in units of (rad/s)/rHz. The input-referred noise of PDH 2 is not shown, but given the same output level would result in roughly 10x the noise contribution to the gyro signal due to the roughly 10x lower optical response of the cavity in the secondary direction.


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