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Entry  Wed Dec 17 13:54:19 2014, Zach, Laser, SiFi, Lasers mounted, energized, beat set up diagram.jpgsetup_with_beat.jpg
    Reply  Wed Dec 17 14:40:15 2014, Dmass, Laser, SiFi, Lasers mounted, energized, beat set up 
       Reply  Wed Dec 17 18:11:38 2014, Zach, Laser, SiFi, Lasers mounted, energized, beat set up 
Message ID: 1183     Entry time: Wed Dec 17 14:40:15 2014     In reply to: 1182     Reply to this: 1184
Author: Dmass 
Type: Laser 
Category: SiFi 
Subject: Lasers mounted, energized, beat set up 

  • With Dmass's help, locking a Zurich PLL to the free-running beat. This appeared to work, and we saw a preliminary frequency noise spectrum that looked about right, but I'm skeptical because the control signal doesn't seem to respond to my slewing one laser's frequency
  • Briefly, locking one laser to the other at low frequencies using the Zurich PLL control signal as a frequency discriminator. This didn't work, adding to my suspicion.

If the "locked indicator" light is not green on the Zurich (first tab, under "Reference", then what you get out is junk (e.g. you have unlocked the lock in, and i hasn't re-acquired yet) - you can do this by kicking it too hard with a frequency shift, which would be easy to do if you were slewing laser frequency, as the coefficients of the laser [Hz/mA] is so big. When the lock in loses the signal, you have to manually re-lock it (toggle off and on the button which has the mouseover text: "enable the fixed center frequency mode of the PLL"). You can get  something which sort of looks like a PLL signal which has terrible noise and weird glitchy response when the lock in isn't locked in.

Your instinct to look for slewing at the PLL control point is correct, and a sign that the state of the PLL is healthy/unhealthy

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