Abstract
A scanning tunneling optical microscope (STOM) is used to directly determine the electromagnetic field amplitude of optically excited surface plasma waves on a silver film. The field amplitudes are measured as a fonction of the angle of incidence of the exciting light beam. The excitation of surface plasmons on the silver film causes a characteristic field enhancement compared to evanescent waves on uncoated surfaces. The measured values for the resonance angle, resonance width and the field enhancement ratio at various wavelengths are compared with theory and with simultaneous measurements of attenuated total internal reflection (ATR). The sensitivity of near-field optical methods to the film thickness is comparable to that of the ATR method. However, while ATR measurements are limited by diffraction, the lateral resolution of STOM can be of the order of 50 nm.
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