V.G.Dmitriev, S.G.Grechin, V.A.Pryalkin
"Frequency conversion in periodically poled nonlinear crystals: possibilities, state of art, perspectives, and limitations"
XVI International Conference on Coherent and Nonlinear Optics, 1998, TuD4, p.14

      Nonlinear crystals with regular domain structure (RDS) attract great interest becaus of possibility to realize quasi-phasematching (QPM) for nonlinear optical processes. QPM techniques allow to use nonlinear materials for which birefringent phase matching isn't possible, to maximize nonlinearity of the materials, to realize such "exotic" nonlinear processes as backward second harmonic generation, optical parametric oscillation with backward wave, etc. There's principle possibility of simultaneous realization of many nonlinear optical processes in RDS crystals (for example, simultaneous generation of second and higher harmonics, optical parametric oscillation with low-frequency pump, and with divisible parametric frequencies). This is why RDS crystals may by widely used in optics investigations and applications.

      In this paper, we discuss modern state of art of laser frequency conversion problem in RDS crystals, of it's progress, and some peculiar limitations. The numerical analysis was carried out using mathematical of reduced equations for coupled waves and Fourier-optics nonlinear diffraction equations.The results of preliminary analysis for wultiwave generation in RDS crystals are presented. We took in consideration about 4000 possible combinations of nonlinear wave interactions. Expression for effective nonlinearity are presented for different orientations of grating wave vector. The effect of pump depletion and coherent lenth dependence on pump intensity are analyzed too. Methods of suppression of undesirable nonlinear optical processes are considered. Peculiarities of noncollinear interaction in RDS crystals are analyzed.

      Results of experimental investigations of laser frequency conversion in facet-type regular domain structure in LiNbO3:Y:Mg crystal are presented