Koji, Craig

Tonight we investigated intensity noise further.  We locked the OMC on just the 45 MHz at 30 watts with 18 dB whitening gain, and then locked it on carrier at 20 W with 0 dB whitening gain.  This is a repeat of here.

We found that carrier and 45 MHz noise levels are similar.  (See attachment one, carrier RIN is Blue, 45 MHz RIN is Brown)

We were confused about why 100 and 1000 Hz the carrier noise is lower.  We believe that this is mostly a shot noise effect.  
For 45 MHz we have 0.5 mA on the OMC DCPDs, while for carrier we had 34.3 mA.  This corresponds to RIN shot noise levels of 2.5 × 10-8 1/rtHz and 3.1 × 10-9 1/rtHz.
- The carrier is mostly limited by the ISS second loop sensing noise, as seen from the green curve in attachment one.  
- The 45 MHz flattens out right around our shot noise limit around 100 Hz.
- Both carrier and 45 MHz have similar RIN spectra below 100 Hz.

Recap:
We know that the 9 MHz modulation depth has a real effect on the DARM noise, seen here as well.  During the holiday party we were able to improve DARM noise by increasing the DARM offset, which could be due to increased carrier drowning out the 9 MHz noise.
We also know that our OMC measured RIN in the sidebands cannot be explained from the noise in our RF AM stabilization scheme, or the ISS.
We are pretty sure that the IMC FSR is reasonably close to our 1f modulation frequency.

Conclusions:
We here note that our shot noise from the OMC sideband measurements is not good enough from 80 Hz onwards to be able to tell what our actual 45 MHz sideband RIN noise level is.  
Below 100 Hz, carrier and 45 MHz RIN seem to be limited by the same mechanism, we don't know what it is.  
9 MHz is not ever limited by shot noise in the OMC RIN measurement, and is overall worse than both carrier and 45 MHz RIN after 20 Hz, where it starts falling much more slowly. (Attachment three)

-------------------------------------------------------------------------------------------------------------

Past OMC carrier RIN measurement