Noncollinear interactions in parametric luminescence

A quantum mechanical perturbation treatment of optical parametric luminescence in nonlinear crystals is briefly given. The expression obtained for the emitted signal power applies to noncollinear phase-matching situations. Next, a detailed analysis of these interactions is given, with results in the form of signal wavelength versus observation angle, with fixed pump direction. The nonlinear crystal is LiNbO3and the pump is one of the lines from an argon ion laser. The effect of temperature is studied. Emphasis is on large observation angle effects, and on the singularities arising from the particular dispersion curves of the crystal. Experimental results provide a good check on noncollinear matching predictions. The far-field signal wavelength dependence on angle as measured from pump beam is approximately quadratic for small angles, and linear for the particular temperature that gives the collinear degenerate interaction. For larger angles, the law is not simple, and there is a limiting cone of directions with no matched signal outside. This cone appears brightest in far field. Applications discussed include the accurate measurement of nonlinear susceptibilities of crystals, the design of tunable optical parametric oscillators, and the measurement of refractive indices in strong absorption regions.