40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
Entry  Tue Mar 3 11:49:16 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise CTN_Trans_RIN_measurement.pdf
    Reply  Sat Mar 7 09:50:31 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop CTN_Trans_RIN_measurement.pdf
       Reply  Wed Mar 11 12:45:15 2020, rana, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop 
          Reply  Wed Mar 11 13:16:09 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop 
             Reply  Wed Mar 11 16:43:55 2020, anchal, DailyProgress, ISS, Comparison between Out of loop vs In loop RIN CTN_Trans_RIN_OOLvsIL.pdf
Message ID: 2551     Entry time: Sat Mar 7 09:50:31 2020     In reply to: 2549     Reply to this: 2552
Author: anchal 
Type: DailyProgress 
Category: ISS 
Subject: Transmitted Laser Relative Intensity Noise - Out of loop 

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

 

Attachment 1: CTN_Trans_RIN_measurement.pdf  215 kB  | Hide | Hide all
CTN_Trans_RIN_measurement.pdf
ELOG V3.1.3-