Not logged in
Tue Mar 3 11:49:16 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise
Sat Mar 7 09:50:31 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop
Wed Mar 11 12:45:15 2020, rana, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop
Wed Mar 11 13:16:09 2020, anchal, DailyProgress, ISS, Transmitted Laser Relative Intensity Noise - Out of loop
Wed Mar 11 16:43:55 2020, anchal, DailyProgress, ISS, Comparison between Out of loop vs In loop RIN
Sat Mar 7 09:50:31 2020
In reply to:
Reply to this:
Transmitted Laser Relative Intensity Noise - Out of loop
Attached are the latest transmitted RIN measurements.
I setup a Thorlabs PDA10CS photodiode at the dumped end of beatnote (
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 (
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.
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.