Scattering of evanescent light by a finite-size probe in near-field scanning optical microscopy

Scattering of the evanescent Light by a finite-size SiO2 probe is calculated using a point matching method in order to improve the efficiency collecting the near-field optical signal. The scattered-light patterns can be classified into three categories. Category 1 is where the probe tip radius is very small (<lambda/13). Category 3 is where the probe radius is very large (>lambda/6). Category 2 is the intermediate case (lambda 13<radius<lambda/6). When the radius is in category 1, the scattered light is able to be treated as a field radiated by the point dipole induced by the evanescent light at the probe tip. When the tip radius is in category 2 (lambda 13<radius<lambda/6), in order to obtain the angular distribution of the scattered light, the induced multipoles should be calculated, considering the probe radius and the incident angle. When the tip radius is in category 3 (radius>lambda/6), the scattered light becomes larger in the parallel direction to a prism surface due to the forward scattering of the evanescent Light. (C) 1996 American Institute of Physics.