Radiation transfer in a spectral line in a nonlinear absorption medium

M. Yamanoi

M. B. Gornyi, D. L. Markman, Boris G. Matisov

B. A. Veklenko, Ganna Tkachuk

E. S. Vorobeichikov, Б. Н. Пойзнер, L. N. Popov +1 more

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.

N. B. Yengibarian, A. Kh

1. Nonlinear transfer theory of coherent or completly noncoherent scattering. It is well known that due to an interaction of the strong radiation field with a medium the local optical properties of the medium depend on the state of the radiation field. At RTSL a strong radiation field reduces due to the high excitation of atoms and as a result, the absorption capacity of the medium decreases (in a series of the ground state) and the effects of stimulated absorption begin to play a role (negative absorption). Then the transfer equation becomes nonlinear. Nonlinear transfer problems (NLTP) are of great importance not only in astrophysics, but also in the theory of quantum optical generators. Until the 1960s the analytical theory of NLTP was absent. Although in that period the physics of local interaction of the strong radiation field was well known. In 1963 the creation of the nonlinear theory of RTSL was undertaken by Academician V. Ambartsumian and his followers. The investigations were carried out in two basic directions: a) application of the principle of invariance (PI) of Ambartsumian to NLTP; b) development and creation of the method of self-consistent optical depths (SCOD). The basic results due to the method of SCOD were obtained. The idea of this method, which was suggested by V. Ambartsumian in 1964, was based on the possibility of exact linearization of NLTP in a homogeneous plane layer by means