Phase matching of optical X-waves in nonlinear crystals

The phase-matching conditions of interacting X-waves in nonlinear crystals are obtained for the first time. The range of X-wave velocities feasible for phase-matching is determined. It is demonstrated experimentally that angular dispersion of the waves excited in optical parametric generator by quasimonochromatic pump corresponds to angular dispersion of nondiffracting pulsed beams.