Polarization of the active medium of a gas laser is calculated on the basis of a system of quantum kinetic equations for density matrix elements with consideration of radiation capture. A precise expression for the actual and imaginary parts of complex polarizability is acquired within the cited approximation. The results are valid for arbitrary fields and for any relations between the relaxation constants. It is shown that capture may noticeably affect the size of the complex polarizability.
Department of General Physics and Wave Processes, Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia