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Tue Dec 3 22:41:17 2019, shruti, Update, General, PLL for PM measurement
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Wed Dec 4 20:32:43 2019, gautam, Update, General, PLL for PM measurement
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Mon Dec 9 21:22:46 2019, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT
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Tue Dec 17 20:08:09 2019, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT
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Thu Jan 16 19:32:23 2020, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT
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Thu Jan 23 20:08:49 2020, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT
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Tue Jan 28 19:40:15 2020, shruti, Update, General, PLL / PM measurement of Xend NPRO PZT 
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Message ID: 15169
Entry time: Tue Jan 28 19:40:15 2020
In reply to: 15148
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Author: |
shruti |
Type: |
Update |
Category: |
General |
Subject: |
PLL / PM measurement of Xend NPRO PZT |
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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:
- I do not understand why the high PI corner frequency of 1kHz or 3kHz was required to lock.
- 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.
- 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.
- 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?
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