Coherent backscattering in nonlinear atomic media: quantum Langevin approach

Abstract

In this theoretical paper, we investigate coherence properties of the near-resonant light scattered by two atoms exposed to a strong monochromatic field. To properly incorporate saturation effects, we use a quantum Langevin approach. In contrast to the standard optical Bloch equations, this method naturally provides the inelastic spectrum of the radiated light induced by the quantum electromagnetic vacuum fluctuations. However, to get the right spectral properties of the scattered light, it is essential to correctly describe the statistical properties of these vacuum fluctuations. Because of the presence of the two atoms, these statistical properties are not Gaussian : (i) the spatial two-points correlation function displays a speckle-like behavior and (ii) the three-points correlation function does not vanish. We also explain how to incorporate in a simple way propagation with a frequency-dependent scattering mean-free path, meaning that the two atoms are embedded in an average scattering dispersive medium. Finally we show that saturation-induced nonlinearities strongly modify the atomic scattering properties and, as a consequence, provide a source of decoherence in multiple scattering. This is exemplified by considering the coherent backscattering configuration where interference effects are blurred by this decoherence mechanism. This leads to a decrease of the so-called coherent backscattering enhancement factor.

19 pages, 1 figure

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• Radiation trapping in a dense cold Rydberg gas
• Pulse area dependence of multiple quantum coherence signals in dilute thermal gases
• Coherent inelastic backscattering of laser light from three isotropic atoms
• Spectrum of coherent backscattering of light by two atoms
• Rigorous derivation of the triple scattering signal from single-atom responses
• Double scattering of intense laser light by two atoms
• Coherent backscattering of intense light by cold atoms with degenerate energy levels: Diagrammatic treatment
• Diagrammatic approach to coherent backscattering of laser light by cold atoms: Double scattering revisited
• Coherent backscattering of light from saturated atoms
• Optical nonlinearity of cold atomic ensemble driven by strong coherent field in a saturation regime