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| Cryo Lab eLog |
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 Tue Jun 29 14:13:53 2021, aaron, DailyProgress, Noise Budget, Calibrating PSOMA noise budget 
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 Wed Jun 30 14:38:49 2021, aaron, DailyProgress, Noise Budget, Calibrating PSOMA noise budget
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Thu Jul 1 13:39:12 2021, aaron, DailyProgress, Noise Budget, Calibrating PSOMA noise budget
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Fri Jul 2 11:29:52 2021, shruti, DailyProgress, Noise Budget, Calibrating PSOMA noise budget 7x
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Tue Jul 6 14:39:49 2021, shruti, DailyProgress, Noise Budget, Calibrating PSOMA noise budget
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Thu Jul 8 09:50:41 2021, aaron, DailyProgress, Noise Budget, PSOMA noise budget, does it make sense?
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Wed Jun 30 17:26:42 2021, aaron, DailyProgress, Noise Budget, Calibrating PSOMA noise budget
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Fri Jul 30 16:55:38 2021, rana, Electronics, Laser, Delay Line Freq Discriminators
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Message ID: 2775
Entry time: Tue Jul 6 14:39:49 2021
In reply to: 2773
Reply to this: 2776
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| Author: |
shruti |
| Type: |
DailyProgress |
| Category: |
Noise Budget |
| Subject: |
Calibrating PSOMA noise budget |
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[chris, aaron, shruti]
- We (Chris, Shruti) noticed that the offset changes on ERC_MON_RATIO when the lights are turned off/ on despite having a long pass filter; it also changes on PDH_CTL_OUT when the slow loop is off. This is probably the main reason why we need to lock the slow controls to an offset of PDH_SET to get the brightest spot.
We (Aaron, Shruti) re-measured the PDH error signal slope for calibration since the previous measurements were for the settings before the mode-matching was optimized.
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drive parameters
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A: pk-pk voltage (mV) |
B: peak separation time (us) |
C: sideband crossing separation (us) |
D: difference in drive at sideband crossings (mV) |
E: cavity pole (MHz) = 33.59/C*B |
F: cavity response (mV/MHz) = A/E |
| 1 kHz, 3 Vpp |
500 |
13.6 |
99.2 |
480 |
4.6 |
109 |
| 5 kHz, 3 Vpp |
478 |
2.96 |
26.1 |
480 |
3.8 |
126 |
The cavity pole has changed but the peak-peak voltage of the PDH error signal seems roughly the same as measured on Thursday before optimizing the mode-matching. It seems like the different temperature setting we are now at has changed the polarization of light entering the cavity; there is no half-wave plate in the path between the fiber launch and input coupler.
Initial crude noise calibration
I used the above estimate of the cavity pole and response along with the data measured on Friday to obtain a calibrated noise spectrum (red curve in Attachment 2), then for data above 100 Hz I used the linear estimate of the open loop gain and roll-off shown in Attachment 1 to obtain the blue curve in Attachment 2.
All data and the jupyter notebooks are in Attachment 3 |
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