Construction of a scanning near-field optical microscope using a white-light source

A scanning near-field optical microscope (SNOM) was constructed using a xenon lamp as a light source. A photon scanning tunneling microscope configuration was used, in which thin-film samples were attached to the surface of a prism, and illuminated by the evanescent field generated by the total reflection of white light emitted by the lamp. The evanescent field was scattered and picked up with a sharpened optical fiber and dispersed with a multichannel spectrometer, yielding the transmission spectra of samples with a spatial resolution of approximately LOO nm. The transmission spectra of two thin-film samples, copper phthalocyanine and gold, were measured with the SNOM and a conventional spectrophotometer. For copper phthalocyanine, the spectra measured with the SNOM and the spectrophotometer agreed well with each other. In contrast, for gold the spectrum obtained by the SNOM exhibited an inverted feature compared to that determined by the spectrophotometer. The origin of the inverse spectrum is discussed based on the surface plasmons locally generated on the gold thin-film surface.