Nutsinee, Sheila, Evan

Thanks to the recent work on violin mode damping, we now have periods where the modes are low enough to engage a second stage of whitening on the OMC DCPDs.

We engaged the second stage of whitening in full lock around 2015-08-14  09:25:00 Z.

This extra whitening lowers the noise in both the sum and null streams (as expected). In the null stream, the improvement is about 4%. This improvement was enough to bump up the range by 2 or 3 Mpc.

[The dc photocurrent on the DCPDs changed negligibly; A went from 9.95(10) mA to 9.90(10) mA, and B went from 10.05(10) mA to 10.10(10) mA. Also note that the very high-frequency part of the sum, where we are apparently not close to shot-noise limited, has stayed the same before and after the whitening change. So it does not seem to simply be a calibration error. See second attachment.]

The in-situ dark noise of the DCPDs (plus the preamp, whitening, and AA chains) was measured in LHO#16656.