A silica colloidal photonic crystal in ethanol solution, whose lattice constant varies with the height of the crystal, was prepared. The Raman intensities of th e ethanol solution induced by a picosecond intense laser were measured at differ ent heights, and two phenomena were found: (1) although the frequency of Raman s ignals generated within the photonic crystal is equal to that of the photonic ps eudogap 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 s ignal is strongly dependent on the height of crystal, the intensity of th e Raman scattering generated within the silicaethanol colloidal photonic crystal does n ot change with the height, i.e. it is insensitive to the pseudogap. These anti i ntuitive phenomena may be directly interpreted using the fact that the propagati on mechanism of the monodirectional incidental laser is intrinsically different from that of the Raman signals from inner light sources inside a photonic crysta l, and the Raman signals scattered by defects deep inside the crystal and genera ted in the surface layer contribute largely to the measured intensities.
下载:
