I'm continuing with cleaning optics. The optics in cyan circles in the attached picture are cleaned today.
One of the RFPD (currently, for RCAV), has no protecting glass, and it is very dirty. I used an air can to blow some dust away.
Most of the improvement in the noise spectrum comes from the cleaning of the RFPD, and it is still dirty.
I notice that there is a peak at 60 Hz coming up in the measurement, there was none before. I have to look into this
and make sure that no electronic noise is coming up.