Raman scattering of ethanol solvent in a photonic crystal with a variational lattice constant

A silica colloidal photonic crystal in ethanol solution, whose lattice constant varies with the height of the crystal, was prepared. The Raman intensities of the ethanol solution induced by a picosecond intense laser were measured at different heights I and two phenomena were found: (1) although the frequency of Raman signals generated within the photonic crystal is equal to that of the photonic pseudogap of the photonic crystal, the Raman intensity attenuation measured is not reduced to the extent of that in the conventional transmission experiment; (2) although the transmission of an incident beam with the wavelength of the Raman signal is strongly dependent on the height of crystal, the intensity of the Raman scattering generated within the silica-ethanol colloidal photonic crystal does not change with the height, i.e. it is insensitive to the pseudogap. These anti-intuitive phenomena may be directly interpreted using the fact that the propagation mechanism of the monodirectional incidental laser is intrinsically different from that of the Raman signals from inner light sources inside a photonic crystal, and the Raman signals scattered by defects deep inside the crystal and generated in the surface layer contribute largely to the measured intensities.