2ND-HARMONIC GENERATION IN KIO3 CRYSTALS WITH A MULTIDOMAIN STRUCTURE

KIO3 is a negative biaxial crystal with space group P1. Under usual conditions of type I phase-matching for biaxial crystals, a slow ray (e(1)(omega)) at a fundamental frequency can be only transformed into a fast ray (e(2)(2 omega)) at a doubled frequency (the refractive index relation is n(e1)>n(e2)), i.e., e(1)(omega)+e(1)(omega) -->e(2)(2 omega). However, with a Nd:YAG laser beam passing through a KIO3 crystal with a multidomain structure along the direction of type I phase-matching, in addition to the e(2)(2 omega) ray at the doubled frequency, a slow ray (e(1)(2 omega)) appears around transmission spot formed by e(2)(2 omega) . We believe that this phenomenon is induced by the multidomain with parallel domain boundaries in as-grown KIO3 crystals.