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