Kinetics of reflected resonance radiation from excited gas media

B. A. Veklenko, R. B. Gusarov, Yu. B. Sherkunov

According to quantum electrodynamics, the cross section for resonant scattering of radiation on an aggregate of excited atoms can be written as a sum of positive definite terms. This type of structure is not consistent with the Fresnel formulas for the reflection coefficient of radiation from thermally excited media. The difference shows up on a macroscopic level and indicates that semiclassical radiation theory cannot be used. A study of the correlation between elastic scattering and stimulated emission processes clarifies the reason for the discrepancies. The resulting singularities require summing of Feynman diagrams which appear beginning in the sixth order of perturbation theory. A lower bound estimate for the reflection coefficient from a plane layer is given, including processes which violate the statistics of radiation. The contribution of stimulated emission processes caused by the initially scattered photon are examined specifically. An experiment is proposed which would settle the choice of theories.

Mark W. Zemansky

M. B. Gornyi, Boris G. Matisov

RBT Black

Diffusely reflected and transmitted spectral line profiles are calculated for uniform noncoherently scattering media onto which radiation of frequency near that of a resonance line of the medium is incident. Profiles are calculated for incident light that is either collimated or unifQrmly diffused and that is either monochromatic, or of uniform frequency distribution, or contains an absorption line centred on the resonance line under discussion. Spectral lines generated by uniformly excited media are also calculated.

J. I. Cotrim Vasconcellos

B. A. Veklenko

A new method for calculating the density matrix of a quantized electromagnetic field which interacts with the environment in the presence of kinetic processes in the medium is suggested. This method accurately takes into account photon-photon quantum correlators and possesses certain symmetry properties, which substantially facilitate the summation of the Feynman diagrams that arise in the calculations. Forward scattering of resonance radiation by two-level gas atoms in a magnetic field is considered as an application. Insufficiency of a semiclassical description of this coherent process in excited media with the use of the unique tensor index of refraction is shown to follow from quantum electrodynamics. The introduction of one more function depending on the frequency of irradiation and the concentration of excited atoms is necessary. Experiments that simultaneously determine both this additional function and the standard refractive index of the medium are specified.