Duration of the second harmonic of quasisingle-mode laser radiation under conditions of strong energy exchange

A direct numerical solution of reduced equations is used to study theoretically second harmonic generation in nonlinear crystals in the case of strong energy exchange. An allowance is made for the aperture effects and for diffraction. It is shown that transformation of single-mode radiation in crystals with critical phase matching is not very inferior in respect of the conversion efficiency to that in crystals with 90° phase matching, and that displacement of an extraordinary wave relative to an ordinary one prevents the reverse energy conversion. It is shown that in the case of a strong energy exchange in crystals with critical phase matching the efficiency of second harmonic generation decreases strongly even in the presence of slight spatial distortions in a transverse cross section of the fundamental-frequency beam.