title: Light generation at the anomalous dispersion high energy range of a nonlinear opal film.
abstract: We study experimentally and theoretically light propagation and generation at the high energy range of a close-packed fcc photonic crystal of polystyrene spheres coated with a nonlinear material. We observe an enhancement of the second harmonic generation of light that may be explained on the basis of amplification effects arising from propagation at anomalous group velocities. Theoretical calculations are performed to support this assumption. The vector KKR method we use allows us to determine, from the linear response of the crystal, the behavior of the group velocity in our finite photonic structures when losses introduced by absorption or scattering by defects are taken into account assuming a nonzero imaginary part for the dielectric constant. In such structures, we predict large variations of the group velocity for wavelengths on the order or smaller than the lattice constant of the structure, where an anomalous group velocity behavior is associated with the flat bands of the photonic band structure. We find that a direct relation may be established between the group velocity reduction and the enhancement of a light generation processes such as the second harmonic generation we consider. However, frequencies for which the enhancement is found, in the finite photonic crystals we use, do not necessarily coincide with the frequencies of flat high energy bands.
authors: Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Barcelona, Spain. muriel.botey@upc.edu
authors: Muriel
authors: M
authors: Botey
authors: Marc
authors: M
authors: Maymó
authors: Alberto
authors: A
authors: Molinos-Gómez
authors: Luis
authors: L
authors: Dorado
authors: Ricardo A
authors: RA
authors: Depine
authors: Gabriel
authors: G
authors: Lozano
authors: Agustín
authors: A
authors: Mihi
authors: Hernán
authors: H
authors: Míguez
authors: Jordi
authors: J
authors: Martorell
mesh_terms: D003460:Crystallization; D008027:Light; D008863:Microspheres; D015233:Models, Statistical; D008962:Models, Theoretical; D055095:Optics and Photonics; D017785:Photons; D011137:Polystyrenes / Q000737:chemistry; D012542:Scattering, Radiation
chemical_list: D011137:Polystyrenes