OBSERVATION OF 2-PHOTON NOISE-INITIATED FLUCTUATIONS IN FAR-INFRARED DICKE SUPERRADIANCE

The anticorrelated fluctuation of the intensity of a driver beam pumping a LAMBDA-like three-level system in the first transition from the initial to the intermediate level and that of the intensity of the radiation generated in the second transition from the intermediate to the final level initiated by noise is observed in an experimental arrangement designed for the investigation of far-infrared Dicke's superradiance. The fluctuation is interpreted as the result of a two-photon back-and-forth transition between the initial and the final level, emitting (absorbing) and absorbing (emitting) photons in the first and the second transition depending on the direction of the two-photon transition. The influence of this two-photon back-and-forth transition on the Dicke's superradiance is discussed.