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Message ID: 2506     Entry time: Mon Dec 30 10:33:33 2019
Author: anchal 
Type: Summary 
Category: Other 
Subject: Summary of questions asked in December 

For the convenience of others, I'm summarizing the open questions I asked on elog in December. Comments on the posts, advice or answers to my questions would be nice.


  • CTN:2492 Why are output powers of these lasers much lower than rated power when diode current is maximum? And why do I see a maxima in South Laser Power when diode current is increased, shouldn't it just increase with diode current monotonically?
  • CTN:2495 Comments on beatnote noise differences with different laser power and modulation depth. Can I infer some good choice of laser power and modulation index from this? Suggestions for more tests on this line?
  • CTN:2496 Rana asked for the latest available photos of FSS RFPDS. We want to add an active notch in the final RF amplifier stage.
  • CTN:2497 There is indeed actual DC offsets at the output of FSS RFPDs RF out. Please cross-verify my measurement method and does this mean the MAX4107s are busted. Should I replace them?
  • CTN:2499 Time series measurement of the signal before and after the summing stage in FSS on Northside. There is significant leftover 1-Omega frequency even after the elliptical filter. I think I need to make the input end lossy to absorb back reflections from the elliptical filter. Need permission to modify the circuit and test if this helps.
  • CTN:2501 There is a logged event of South Laser losing about 20% of its output power with the same diode current. Is this laser dying? What is happening?
  • CTN:2505 As instructed, I have taken transfer functions through FSS from PZT path and EOm path to RIN before and after the PMC. I need validation on method used. My conclusion is the noise in FSS is due to RIN and not the other way round (FSS causing RIN).  I tried taking an OLTF of the PMC loop but the NPMC Loop unlocks as soon as I connect the source port of AG4395A to an excitation port in a summing stage. So I've been unable to verify the source of this RIN yet, but previous measurement (CTN:2502) suggests it is PMC.

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