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Near-field Raman imaging of organic molecules is demonstrated by an apertureless near-field scanning optical microscope, the tip of which is a silver-layer-coated cantilever of an atomic force microscope ͑AFM͒. The virtue of the enhanced electric field at the tip apex due to the surface plasmon polariton excitations enhances the Raman scattering cross sections. This phenomenon allows us to reveal from near-field Raman images the molecular vibrational distributions of Rhodamine6G and Crystal Violet molecules beyond the diffraction limit of a light. These molecular vibrations cannot be distinguished by AFM topographic images.

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The photoisomerization of disperse red 1 (DR1) in polymethylmethacrylate thin films is demonstrated by monitoring the refractive index variations by the attenuated total reflection method. Absorption spectrum measurements give a confirmation of this phenomenon. The kinetics of photoisomerization and of thermal relaxation are nonexponential. Some other molecules are studied. As in solution, azobenzene derivatives (N—N) produce reversible isomerization while dimethylaminonitrostilbene, a stilbene derivative (C—C), exhibits no thermal cis→trans relaxation.