FORBIDDEN LIGHT SCANNING NEAR-FIELD OPTICAL MICROSCOPY

Near-field optics (NFO) opens the door to light microscopy techniques with resolutions well beyond the diffraction limit, The richness of op tical investigations is now applicable on a near-molecular level, Amon g the novel scanning near-field optical microscopy (SNOM) schemes, the most prominent representatives are aperture SNOM and scanning tunnell ing optical microscopy (STOM or PSTM). New experimental and theoretica l work has to be performed to study the phenomena specific to NFO. One such example is the angular dependence of light emission in aperture SNOM. The detection of radiation at angles greater than the critical a ngle of total internal reflection alpha(c)=arcsin(n(-1)), where n is t he sample refractive index, can represent a microscopy scheme that com bines the respective advantages of both aperture SNOM and STOM, Recent experiments have demonstrated the expected exponential dependence of light intensity on gap width (for fixed emission angle alpha > alpha(c )). The decay length as a function of a is in agreement with the Fresn el description of the evanescent field when total reflection occurs at an interface, These investigations were additionally motivated by cal culations based on the multiple multipole method.