Method for compensating the phase-matching dispersion in nonlinear optics

A method for compensating the angular dispersion of the phase matching in frequency doubling is developed theoretically for a collinear but basically nonmonochromatic pump radiation. The method is based on a preliminary modification of the pump beam by passing it through a medium with an angular dispersion close to the phase-matching dispersion. When this compensation method is used, the intensity of the second harmonic can be increased by an order of magnitude or more. Illustrative numerical calculations are made for KDP, LiNbO₃, LiIO₃, and proustite crystals. It is shown that the method can suppress successfully the influence of fluctuations of the pump frequency on the second-harmonic intensity. The method was tested experimentally by generating the second harmonic of neodymium-glass laser radiation (spectral width 8 nm) in LiIO₃, by the оо–е interaction. An increase in the integrated intensity of the second harmonic by an order of magnitude was achieved.