Second harmonic generation in periodic and aperiodic transversely poled crystals

One of the greatest advances in the field of second-harmonic generation (SHG) has been brought about by the use of multi-domain crystals with periodic or aperiodic alteration of the sign of the quadratic nonlinearity. All applications involving the SHG process, however, rely on the propagation of the fundamental beam in the plane perpendicular to the ferroelectric domain walls. In this paper the authors realize a transverse geometry, when the fundamental beam propagates along the normal to the plane of nonlinearity modulation. The authors report on the observation of ring-type SHG and new type nonlinear diffraction patterns utilizing Z-cut samples with different types of modulation of their quadratic nonlinearity: (a) rectangular periodically poled structure patterned in stoichiometric LiTaO₃ (RSLT); (b) annularly poled structure in stoichiometric LiTaO₃ (ASLT); (c) short-range ordered poled structure patterned in LiNbO₃ (SRO-LNB); (d) nonlinear photonic octagonal quasi-crystal sructure patterned in LiNbO₃ (OQC-LNB); and (e) disordered nonlinear photonic structure such as unpoled SBN (DNPS-SBN).