Four-photon parametric frequency selection in wide stimulated emission lines
It is shown theoretically that the interaction between coherent light waves may give rise to periodic structures of parameters such as the refractive index, the absorption, and population inversion, etc. These structures can act as frequency-selection elements of the diffraction grating or the multilayer mirror type. Numerical estimates are obtained for some cases which satisfy formally the phase matching conditions for the four-photon interaction. Particular consideration is given to the case of coherent pumping of a dye-solution laser in which the frequency of the laser emission within a wide line can sometimes be altered.