Vibrational spectra of polyacetylenes

A considerable amount of information about optical and electronic properties of polyacetylenes has been obtained during the last decade from vibrational spectroscopy. In this lecture several basic points not yet fully understood will be discussed and a new method for evaluating the vibrational density of states for random defects will be presented

Optical study of artificial opals as 3D photonic crystals

Artificial opal films have been prepared by sedimentation of monodisperse silica spheres in water suspension. Atomic force microscope images show a triangular packing of the spheres at the surface of the films. The presence and the energy position of an optical pseudo gap in incidence-angle-dependent transmittance and reflectance spectra is observed and accounted for by theoretical calculations of the photonic band structure. These calculations indicate that the pseudo gap is due to the splitting of the photonic bands in the L point of the Brillouin zone. The spectroscopic data show additional loss structures due to both other features of the Brillouin zone and the diffraction of the light from the regular surface of the sample. The effect of the infiltration of opals with polydiacetylene solutions is also reported