Jenne Sheila

Summary:

We measured the RIN on the 9 MHz sideband 00 mode through the OMC, and see that it is about a factor of 10 higher than the RIN predicted by the RF AM monitor.  

Details:

The first time I tried this measurement, we were limited by the OMC DCPD dark noise 46197.  These are the steps we followed this time:

• engage 3 whitening stages + 18dB whitening gain on OMC DCPDs, measure DCPD dark noise with IMC offline (18:51 UTC Jan 17)
• Lock IMC at 2 W, request guardian to ISS_ON (we have to engage ISS before powering up, but can't DC couple it until we are powered up, don't use ISS_AC_COUPLED state)
• increase power to 30W using Power guardain
• ISS DC coupled
• Align IFO for single bounce, engage AS centering loops, OMC ASC
• reduced 45MHz modulation depth to 3.3dBm on driver, increased 9 MHz to 27dBm
• turn off OMC whitening (no filters, 0dB gain), and reduce OMC length dither line to 0 to take OMC scans to identify 9MHz modes
• turn dither line and whitening back on, lock OMC on 9 MHz mode
• measurement with no excitation: 19:25 UTC
• enable excitation on EOM driver, measurement with excitation at 19:31:59 UTC

The OMC DCPD signals (and dark noise) are calibrated into RIN here taking into account the extra 18dB of whitening gain.  The EOM driver channel is normally calibrated into RIN assuming that the drive level is 17dBm according to Daniel, so this is divided by 3 because we are using 27dBm out of the EOM driver here. 

The measurement with the excitation on shows good agreement between the RF AM monitor and the measured amplitude noise, so these calibrations are OK.  We also have OK clearance above dark noise and the intensity noise seen by the ISS. So there is some additional source of intensity noise on the 9 MHz sidebands.