Resonance Absorption of Radiation in an Inhomogeneous Medium with Variable Sign of the Coefficient of Absorption

A. P. Khapalyuk

С. И. Грачев

J. I. Cotrim Vasconcellos

Using the exact solution for a sine-driven two-level system we have calculated the nonlinear absorption coefficient of a gas of two-level molecules with homogeneous (hard collisions, spontaneous decay) and inhomogeneous (Doppler effect) broadening mechanisms. We have studied the dependence of the form of the absorption lines on relaxation parameters, on the strength of the electric field, and for various ratios between the homogeneous and inhomogeneous linewidths. We include considerations about saturation of the medium caused by the external field that gives rise to the so-called power broadening of the spectral lines. The dependence of the linewidth on the saturation parameters and on the relaxation parameters is determined. These parameters appear in the ratio of the purely homogeneous and purely inhomogeneous linewidths. Asymptotic behaviors of this linewidth for the homogeneous limit and for the inhomogeneous limit are also determined.

Андрій Сіжук, Konstantin E. Dorfman, C. H. Raymond Ooi

The spatial inhomogeneity of absorption coefficient of the space between mirrors, filled by an optically active gas, is analyzed in quantum optical terms. It was theoretically shown, that the quantization of electromagnetic field in a cavity (optical resonator) can reveal the spatial inhomogeneity of absorption or re-emission ability of the optically active medium. It appears from the analytical calculations, the inhomogeneity is caused by the Doppler frequency shifts (including recoil effects) during the atom-photon collisions and the non-zero initial frequency width of the scanning signal. The proposed analytical representation of the absorption coefficient through the additive quantum optical terms gives deeper insight into intrinsic processes in the interacting with light matter.

H. Henssen

V. E. Khartsiev

The phenomena which take place during the time of propagation of a monochromatic pulse of a resonance radiation through optically dense on the transition frequency medium containing resonance absorbing centers are considered. Due to the action of the pulse of the resonance radiation the saturation of absorption in the layer of the medium takes place. As a result the absorption decreases in the layer and the radiation penetrates into the next layer. Thus translucent region continuously moves deeper into the medium and the process is wavelike.When the density of the initial photon flux is constant and the distribution of absorbing centers is homogeneous the absorption coefficient and the photon density in the depth of the media depends only on the variable $t\phantom{\rule{0.15em}{0ex}}\ensuremath{-}\phantom{\rule{0.15em}{0ex}}x/v$. The velocity of translucency wave v may be by several orders of magnitude less than the velocity of light. The mechanism of the saturation can be various. The small value of the loss of photons in the transluced region of the medium is the necessary condition for the rise of translucent waves. The condition of realization of translucent wave is fulfilled for a large number of condensed states having intense absorption lines. These conditions are the most favourable in the case of presence of methastable levels between the levels 1 and 2 (type-ruby system). The effect of the translucent waves is general for various ranges of spectrum of electromagnetic radiation and may be realized in astrophysical scale.