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Tue Mar 3 11:49:16 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise
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Sat Mar 7 09:50:31 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop
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Wed Mar 11 12:45:15 2020, rana, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop
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Wed Mar 11 13:16:09 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop
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Wed Mar 11 16:43:55 2020, anchal, DailyProgress, ISS, Comparison between Out of loop vs In loop RIN
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Message ID: 2551
Entry time: Sat Mar 7 09:50:31 2020
In reply to: 2549
Reply to this: 2552
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Author: |
anchal |
Type: |
DailyProgress |
Category: |
ISS |
Subject: |
Transmitted Laser Relative Intensity Noise - Out of loop |
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Attached are the latest transmitted RIN measurements.
Measurement:
- I setup a Thorlabs PDA10CS photodiode at the dumped end of beatnote (15, 13).
- Then, I took out-of-loop RIN measurement of transmitted light by blocking either the North or the South path falling on the beatnote beamsplitter (11, 19).
- I found out that, when the cavity transmission photodiodes are connected to Acromag input, the acromag input injects some noise into the ISS.
- On disconnecting the acromags, I was able to increase gains in ISS loops to 20000.
- A major issue was to measure DC power together with the spectrum to calculate the RIN. I first connected the measured photodetector to Acromag Cavity Transmission Channels (which are empty now) and measured the ratio of DC level with the cavity reflection photodiode.
- Later, using the cavity reflected dc level and this ratio, I was able to estimate the dc level of the spectrum I'm measuring. This way, I ran RIN measurements sequentially for North and South transmitted light.
- The measurement is done by running SR785 repeatedly with no averaging and saving all the curves. 500measurements were attempted, few of them had file transfer errors and were ignored.
- The median, lower bound (15.865% percentile (lower 1-sigma for Normal Distribution)) and upper bound (84.135% percentile (upper 1-sigma for Normal Distribution)) are calculated.
Inference:
- Higher gain improved the noise a little bit more upto 30 kHz.
- Notice that there are 60 Hz harmonics (both odd and even) in the South RIN, while they are not present in the North RIN.
Data
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