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

Second order nonlinear processes in 3D centrosymmetric materials, as second harmonic generation (SHG), have been demonstrated in the past using self organized colloidal suspensions of modified polystyrene spheres in water. This paper demonstrates 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. The photonic crystal properties of the material allows 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.