Intensity noise to the beatnote transfer function

• I resurrected the AEOM power control lines with SMA cables to junction plate on the north side.
• AEOM was driven in linear amplitude modulation regime by aligning input polarization to s (vertical) and making output polarization circular by a quarter waveplate and dumping the s (vertical) polarization through a PBS.
• 
• For the New Focus 4103 models, we have,  . I used source signal for amplitude modulation of  . This gives modulation index  and maximum deviation from linearity by  .
• The measurement was done as a swept sine with input at reference signal as the modulation signal to the AEOM and output as PLL control voltage.
• The TF is then converted to units of Hz/W using PLL actuation slope of 5 kHz/V. The gain in the PLL loop was set to 100.
• Beat note frequency during the measurement was near 135 MHz.
• For the measurement in the North path, Settle Cycle was set to 10 and integration cycle was set to 10.
• During the measurement in the South path, the beatnote started drifting faster so Settle Cycle was set to 2 and integration cycle was set to 4 and average of 3 measurements is taken.
• PFA transfer functions. Note, transfer functions are mentioned from different initial points for future use. They were converted by scaling down by the ratio of the DC power measured at Cavity input, PMC output, and AEOM output.

Transmission RIN:

I measured transmission RIN before the beatnote measurement. Unfortunately, we can not compare with earlier intensity noise measurement I took because I didn't take transmission power measurements then.

These measurements were taken in 4 steps of frequency ranges and stitched together. See the attached notebook for further details.

Beat Note Frequency Noise Spectrum

I used the same measurement method as explained in (PSL:2272). Following are some experiment state measurements I made:

Note: I also found that half waveplate behind North FSS EOM had no marked order and was probably multi-order. I replaced it with a zero-order half waveplate and found significant improvement in RFAM at Cavity Reflection RFPD. Above mentioned numbers were taken after this change.

Updated Noise Budget:

I'm still using the old code here as there are some unresolved questions with the new code I want to be sure about first.

• The new spectrum is lower at noise at lower frequencies. This might be due to the unmeasured amount of light falling on the cavities in the previous measurement.
• RFAM and RIN tuneup decreased noise slightly at 2 and 3 kHz.
• However, the method used for taking these measurements keeps the uncertainty high. So maybe the effects of our changes are actually negligible and something else is more pressing.
• Clearly, the growth of noise beyond 1 kHz is still happening and this is one major difference between earlier noise measurements and new measurements.
• I think installing ISS should be the next step in the queue because these high-frequency bump is probably coming from there.
• I will also work on tuning up the FSS loop parameters to see if that changes anything.