Frequency dependence of the photonic noise spectrum in an absorbing or amplifying diffusive medium
Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands
2 L.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, Kosygin 2, Moscow 117334, Russia
Corresponding author: a firstname.lastname@example.org
Published online: 15 February 2001
A theory is presented for the frequency dependence of the power spectrum of photon current fluctuations originating from a disordered medium. Both the cases of an absorbing medium ("grey body") and of an amplifying medium ("random laser") are considered in a waveguide geometry. The semiclassical approach (based on a Boltzmann-Langevin equation) is shown to be in complete agreement with a fully quantum mechanical theory, provided that the effects of wave localization can be neglected. The width of the peak in the power spectrum around zero frequency is much smaller than the inverse coherence time, characteristic for black-body radiation. Simple expressions for the shape of this peak are obtained, in the absorbing case, for waveguide lengths large compared to the absorption length, and, in the amplifying case, close to the laser threshold.
PACS: 42.50.Ar – Photon statistics and coherence theory / 05.40.-a – Fluctuation phenomena, random processes, noise, and Brownian motion / 42.68.Ay – Propagation, transmission, attenuation, and radiative transfer
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001