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Entry  Mon Apr 11 16:44:46 2011, Zach, Laser, GYRO, oscillator phase noise measurements gyro_noise_with_phase_noise_contribs_4_8_11.pdf
    Reply  Mon Apr 11 17:07:54 2011, Alastair, Laser, GYRO, oscillator phase noise measurements 
Message ID: 1387     Entry time: Mon Apr 11 16:44:46 2011     Reply to this: 1388
Author: Zach 
Type: Laser 
Category: GYRO 
Subject: oscillator phase noise measurements 

EDIT: I should have mentioned that rotating the polarization before the EOM in order to minimize the error signal offset did not have a noticeable effect on the bulk of the low frequency noise. It did, however, make the coherent-looking peaks from 100-600 mHz go away, though I have no materials to support this.

Also, by placing a PDA255 after the initial beam splitter and demodulating it at the sideband frequency, I observed that the RFAM noise is flat well above the frequencies where we see the excess noise. This isn't purest way to rule it out, but I think it is convincing: if the noise we see at low frequencies is from RFAM, we would see it extending to higher frequencies.


 Below are the (delayed) results of Friday's oscillator noise measurements, calibrated to gyro units and plotted alongside the gyro noise. The traces are:

  1. Gyro noise from AOM actuation
  2. Gyro noise from PLL actuation
  3. Two marconis with fcarr = 100 MHz and dev = 100 kHz/V beating together, with the beatnote fed back to one and the other's dev input shorted. This is divided by sqrt(2) to estimate the noise from the PLL oscillator alone in gyro mode. It agrees pretty well with (2) in the region we think is dominated by oscillator noise.
  4. Two marconis with fcarr = 50 MHz and dev = 100 kHz/V beating together, with the beatnote fed back to one and the other's dev input shorted. This is multiplied by sqrt(2) (i.e., 2/sqrt(2)) to estimate the noise from the AOM actuator alone in gyro mode, taking into account the double pass. This agrees pretty well with (1) in the region we think is dominated by oscillator noise
  5. This isn't really an oscillator phase noise measurement. It is the feeback signal to the PLL oscillator with the modulation on the AOM off (i.e., no gyro signal). This is significant in that, since it is roughly equal to the estimated PLL oscillator noise at low frequency, it rules out the possibility that the excess LF noise comes from phase noise in the output MZ. Therefore, the excess noise must be noise imparted on the CW light by the secondary loop. This helps narrow things down.

gyro_noise_with_phase_noise_contribs_4_8_11.pdf

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