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Entry  Tue Feb 22 21:57:02 2011, frank, tara, DailyProgress, BEAT, beat  beat_2011_02_22.png
    Reply  Wed Feb 23 01:47:15 2011, frank, DailyProgress, BEAT, beat  
Message ID: 509     Entry time: Wed Feb 23 01:47:15 2011     In reply to: 507
Author: frank 
Type: DailyProgress 
Category: BEAT 
Subject: beat  

you have to be a bit more precisely fro points 2 and 3, e.g. no one knows what you mean as "PDH" gain as you have two loops using the PDH technique.

Some comments:

  • For Point 1: What does it mean "and the range of the gain we can adjust is quite high, between 5 - 30 dB" ? From you description it could be that the gain adjustment is limited by loosing lock below gain of 5dB or lower, but you can actually change it from -20 to 30dB without loosing lock. Forgot to mention that the noise does not stay the same if you change the gain below that value. If you lower it below a threshold you see that you don't have enough gain to suppress the laser noise. Only for gains above ~5dB or so you have enough gain and so for the setting we typically use we are not gain limited.
  • For point 2: You forgot to describe what happens when you change the optical power . Reducing the sideband power causing a higher noise floor and not be able to bring it back by increasing the gain is not surprising, e.g. the power is so low that the shot noise level limits you. Then you can't win with more gain. You have to calculate that level and compatre it before you can make a statement.
  • For point  3: Describe a bit more detailed what you changed, no one understands it. Which noise projection did you use, PDH box terminated or with photodetector? That's a huge difference. The noise of the box can be well below and you are still limited by electronic noise from the detection! You should work on that block diagram with all the parts and individual noise sources to get a better picture of what's going on and which noise couples in which way.


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