Phase matching for difference frequency generation in the view of spontaneous Raman scattering by hot polaritons

Abstract

Difference frequency generation between the radiation of a CO2, laser in the infrared and a Kr+ laser in the visible is studied on the materials LiNbO2, and Gap. Both the lasers are used in the continuously working mode. The results are discussed in the well known view of non‐linear optics where phase matching is related with a coherence length and in the picture of spontaneous light scattering by “hot polaritons”. The phase mismatch Δk in the latter case follows directly from a simultaneous solution of the polariton dispersion relation and momentum conservation for spontaneous light scattering. This provides a convenient graphical interpretation of Δk in the ω, k diagram which is of advantage in spectral regions with dispersion.