We measured the beat after a few changes in the setup (modulation index, air spring, small enclosure around the beat). We update the noise budget with suppressed laser frequency noise and Marconi's frequency noise in ACAV loop as well. There is not much improvement in the overall beat noise.
A few changes in the setup:
* The table legs have small leaks, so we have air compressor to keep the pressure high, PSL:880. It works once every hour when the pressure is low. The change of pressure can screw up the beam alignment a lot (for example, DC readout from RCAV RFPD can be varied from 100mV - 1.2V, with 1.7V maximum value (off resonance). I think it affects the alignment to AOM and change the diffraction efficiency/ beam shape as well. It also changes the seismic isolation property. The peaks around 10 Hz show up when the pressure is low. I'll find new legs from New Port and ask for the quote.
==Plan for the next few days==
1) Try using DAQ to measure beat signal, see if we can get rid off the frequency noise from PLL
2) Find out about the new legs(prices/availability)
3) Make the acoustic enclosure box around the whole setup
4) Work on the design for new vacuum windows.