Quantum correlation measurement of laser power noise below shot noise

In this Letter, the quantum correlation measurement technique as a method of power noise monitoring is investigated. Its principal idea of correlating two photodetector signals is introduced and contrasted to the conventional approach, which uses only a single photodetector. We discuss how this scheme can be used to obtain power noise information below the shot noise of the detected beam and also below the electronic dark noise of the individual photodetectors, both of which is not possible with the conventional approach. Furthermore, experimental results are presented, that demonstrate a detection of technical laser power noise one order of magnitude below the shot noise of the detected beam.