LIGO Document T1700131-v1

Time domain implementation of DCPD cross correlation

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T - Technical notes
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This document presents a time domain implementation of the cross correlated DCPD spectrum which suppresses sensing noises such as photon shot noise. The idea is to implement an additional signal stream in the front end digital system and produce a pair of artificial channels such that the cross correlated power spectrum of them then yields such sensing noise free spectrum. As opposed to the offline implementation based on a frequency domain consideration, this scheme offers two advantages: (1) calibration of the resulting spectrum is automatically achieved as it makes use of the existing calibration front end system and (2) it allows easy access to the cross correlated spectrum in the control room because it can be handled by DTT.
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