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Entry  Tue Dec 3 22:41:17 2019, shruti, Update, General, PLL for PM measurement  PM_measurement.jpeg
    Reply  Wed Dec 4 20:32:43 2019, gautam, Update, General, PLL for PM measurement  
    Reply  Mon Dec 9 21:22:46 2019, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT 
       Reply  Tue Dec 17 20:08:09 2019, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT 20191217.png
          Reply  Thu Jan 16 19:32:23 2020, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT 
             Reply  Thu Jan 23 20:08:49 2020, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT Image-1.jpg
                Reply  Tue Jan 28 19:40:15 2020, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT PMTF.pdfBeatSpectrum.pdf
Message ID: 15169     Entry time: Tue Jan 28 19:40:15 2020     In reply to: 15148
Author: shruti 
Type: Update 
Category: General 
Subject: PLL / PM measurement of Xend NPRO PZT 

Over the past few days, I have been trying to make measurements of the phase modulation transfer function by modulating the X end laser PZT via PLL.

The setup was modified every time during the experiment in the same manner as mentioned in elog 15148.

I could not make the PLL lock for long enough to take a proper TF measurement, resulting in TFs that look like Attachment 1. The next step would be to use the method of a delay line frequency discriminator instead of the PLL.


Comments about locking with LB1005 PI controller:

  1. I do not understand why the high PI corner frequency of 1kHz or 3kHz was required to lock.
  2. The rms level of the error signal when locked was ~100 mV, which is 25% of the total mixer range (~400 mVpp). Decreasing the gain only caused the loop to go out of lock and did not decrease this noise in the error signal.
  3. The setup was also partly inside the PSL enclosure, with the HEPA turned to 100%, which is probably a noisy environment for this measurement. Closing and opening the shutters or any disturbance near the enclosure resulted in movement of the beat note up to 5 MHz.
  4. It may have been a better idea to actuate the PSL laser instead of the X NPRO because of its larger range, but would this solve the issue with the noise?
Attachment 1: PMTF.pdf  17 kB  | Hide | Hide all
PMTF.pdf
Attachment 2: BeatSpectrum.pdf  23 kB  | Hide | Hide all
BeatSpectrum.pdf
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