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Message ID: 390     Entry time: Mon Jan 30 12:28:03 2012
Author: Giordon Stark 
Type: DailyProgress 
Category: Coating Q 
Subject: Lock-in Amplifier Fun 

 [Giordon, and Zach came along]

So, we grabbed (nabbed) a chopper from the 40m and stuck it on our set-up in between the linear polarizer and the PBS.

  • Zeroed out the signal on the oscilloscope and then turned on chopper to 1kHz
  • Verified that the square signal we see on the oscilloscope had a frequency of 1kHz corresponding to the chopper freq (attached picture shows Ch1 being the photodetector output, Ch2 being the chopper output - shows they have the same freq)
  • Plug it into the lock-in amplifier and do a calibration at 1 Volt sensitivity to get a factor of 4.375
  • Verified that this factor is linear by changing the signal power and noticing predictable changes in the LIA output
    • this was done by unbalancing the signal power (so we look at the output of one over the other) - calibrating on a balanced output (theoretically zero) makes no sense
    • then we changed the phase of the chopper output to maximize the LIA output
    • then we measured the LIA output versus the photodetector output (e.g. 1.4 V LIA against 320 mV PD)

I apparently have a Bioethics class which got rescheduled for today at 1pm - so that kinda cuts into plans for the rest of the day. Wednesday morning - I'll come into lab and do the test runs mentioned within the manual for the LIA SR830.

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