Semiclassical representation method in statistical physics of interacting molecules. II. Theory of open systems. Application to the theory of a single-mode laser taking into account the recoil effect

The generalization of the earlier reported semiclassical representation method for open systems is given. The quantum theory of a single-mode laser based on two-level atoms having translational degrees of freedom is considered as an example of using the developed approach. Correlation of the field and the atomic motion due to the recoil effect is taken into account in the system under consideration. The self-consistent theory describing dynamic and statistical properties of the system is performed. It is shown that, due to a friction of resonant atoms in a buffer gas, their translational motion is coupled with the radiation field. This coupling can lead to a nonequilibrium form of the atom velocity distribution function which results in essential changes of the field parameters, such as radiation intensity, frequency shift, line width, etc.