A Concept of Cantilevers Optical Dimension for Optimal Application to Cantilever-Based Near-Field Scanning Optical Microscope and Its Measurement

A guide to the selection of the apertured cantilever probe and the numerical aperture of objective lens used in a near-field scanning optical microscope (NSOM) is suggested by defining the Optical dimension of conventional cantilever probe, for achieving highest optical image contrast. An optimized combination between the geometry of the cantilever probe and numerical aperture of the objective lens should be decided for conventional optical head assembly of AFM-based NSOM consisting of cantilever probe and high numerical aperture objective lens, to ensure the light scattered from the specimen being screened by the umbra of cantilever probe, resulting in the light transmitted through the aperture being collected by the objective only. Here, introduction of the optical dimension of cantilever probe, which defines the power of screening the scattered light by the cantilever, conveniently gives us numerical values denoting probe geometry which is critically correlated with the numerical aperture of objective lens with optimized imaging properties. We provide a standard definition of the cantilevers optical dimension.