Second-harmonic generation in KIO₃, crystals with a multidomain structure

Abstract

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^ω ₁) at a fundamental frequency can be only transformed into a fast ray (e^2ω ₂) at a doubled frequency (the refractive index relation is n^e₁ > n^e₂ ), i.e., e^ω ₁+e^ω ₁. → e^2ω ₂ 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^2ω ₂ ray at the doubled frequency, a slow ray (e^2ω ₁) appears around transmission spot formed by e^2ω ₂. We believe that this phenomenon is induced by the multidomain with parallel domain boundaries in as-grown KIO₃, crystals.