SELECTIVE REFLECTION OF RESONANCE RADIATION FROM EXCITED MEDIA

According to quantum electrodynamics, the cross section for resonant s cattering of radiation on an aggregate of excited atoms can be written as a sum of positive definite terms. This type of structure is not co nsistent with the Fresnel formulas for the reflection coefficient of r adiation from thermally excited media. The difference shows up on a ma croscopic level and indicates that semiclassical radiation theory cann ot be used. A study of the correlation between elastic scattering and stimulated emission processes clarifies the reason for the discrepanci es. The resulting singularities require summing of Feynman diagrams wh ich appear beginning in the sixth order of perturbation theory. A lowe r 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 initia lly scattered photon are examined specifically. An experiment is propo sed which would settle the choice of theories. (C) 1998 American Insti tute of Physics.