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Entry  Wed Sep 26 03:31:51 2012, Zach, Laser, GYRO, PSL/Gyro beat setup PSL-Gyro_beat.png
    Reply  Thu Sep 27 03:33:55 2012, tara, Laser, GYRO, PSL/Gyro beat setup beat_2012_09_27
Message ID: 1774     Entry time: Thu Sep 27 03:33:55 2012     In reply to: 1772
Author: tara 
Type: Laser 
Category: GYRO 
Subject: PSL/Gyro beat setup 

Found the beat, the temperature on CTN laser is 48.80 C, and gyro laser is 54.72 C for a 20MHz beat signal.

beat_2012_09_27

Before trying to scan the laser by changing the temperture, I suspected that we did not see beat yesterday because either,

  1. the PD might be broken,
  2. the alignment was bad, the beams were not well overlapped

So

  • I switched the PD with the 1811 one used in my beat setup, and re-aligned and mode-matched the beams again.  This was the hard part because of the very limited and hard to reach space.
  • unplugged feedback signals (fast and slow) from both lasers, since these inputs could effect the actual frequency of the laser and the temperature readout would not change accordingly, (I have not plugged them back yet if you want to lock gyro, you need to plug them back),
  • scanned the laser by turning the temperature knob. As I did not know what was the calibration between T to frequency, I used my PMC to get a rough estimate, and I got something like 0.01 C = 100MHz. Since the PD's bw was upto ~ 200 MHz, I turned the knob at 100MHz (0.01C) step. Once I found the beat, I checked the calibration from gyro laser T to frequency. It was 0.01 C = 2MHz. The numbers were largely different, I might got it wrong, I'll check a gain.

 

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