Kinetic Theory of an Optically Pumped Gas.
Scientific interim rept.,
BROWN UNIV PROVIDENCE R I
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Kinetic equations are presented which successfully incorporate the effects of atomic line radiation on the spatial and time evolution of the velocity distributions of a radiating gas. The equations are applied to the steady state optical excitation of a free molecular slab of two level atoms in a model of the optically excited laser amplifier. Iteration on the coupled kinetic equations and equation of radiative transfer is used to construct a first approximation to the velocity distributions in the optically thick limit. This corresponds to integral iteration in kinetic theory. By performing certain quadratures over the first order velocity distribution for particles in the excited or upper lasing state, it is possible to calculate the inversion density as well as all the radiative properties of the gas. An asymptotic theory is given for the density in the limit of weak external radiation and for two wall reflectance conditions. Also an interesting bimodal behavior of the emission profile is seen. The line shape of the emitted radiation is constant in the line core for about one Doppler width, then it reaches a sharp peak before a Gaussian decay in the far wings. Author
- Lasers and Masers
- Atomic and Molecular Physics and Spectroscopy