High band anomalous group velocity dispersion for the enhancement of the nonlinear interaction

Abstract

Second order nonlinear processes in 3D centrosymmetric materials, as SHG, have been demonstrated in the past using self organized colloidal suspensions of modified polystyrene spheres in water. Taking advantage of the phase matching conditions provided by the photonic crystal and the local braking of the symmetry at the sphere-water interface, the generation of visible SH light is possible.[1]In the present paper we demonstrate that SHG is also possible when modified polystyrene spheres are assembled in a close packing configuration using a method based on the spin coating of a concentrated suspension of polystyrene spheres.[2] In this later case the photonic crystal properties of the material allows us to take advantage of the longer interaction time due to the slow group velocity of the generated light that couples with one of the flat bands that opens at high energy levels. Such small group velocity provides an enhancement mechanism for the nonlinear process. In figure 2 one sees the reflection maximum around 400nm due to one of the first high energy bands for such nonlinear opals. Fig.1. Reflection and SEM picture of a nonlinear opal made of polystyrene spheres modified with a nonlinear organic material.Fig.2 Specular reflection spectrum of the nonlinear opal shown in Fig 1.