Theory of stimulated Raman emission accompanied by the excitation of polaritons in an optical resonator

A theory is given of the steady-state stimulated Raman emission at the Stokes frequency, accompanied by the excitation of polaritons. The emission takes place in an optical resonator with plane-parallel mirrors in which only one longitudinal mode is excited. The range of strong polariton absorption is considered. The pumping wave is assumed to be traveling at a small angle Θ with respect to the resonator axis. The excited polariton wave is also of the traveling type. Expressions are obtained for the stimulated emission threshold, for the fluxes of the energy emerging from the resonator at the Stokes and polariton frequencies, and for the law of attenuation of the pumping energy during its propagation in the resonator. It is shown that the coefficient representing the conversion of the pumping radiation into the Stokes wave rapidly reaches saturation above the threshold and it is close to unity when the excess over the threshold is a factor of 2–3. The stimulated emission frequency for a fixed value of Θ is governed by the competition between the polariton and phonon scattering lines. It is shown that the parameters of a crystal must satisfy a simple condition in order that a polariton line should take an active part in the stimulated emission.