Nanoscale Probing of Dielectric Interfaces with Single-Molecule Excitation Patterns and Radially Polarized Illumination

Abstract

We present new results on the theoretical and experimental study of the excitation patterns acquired upon scanning a single molecule through the focal region of a radially polarized laser beam when the emitter is located at a glass–air interface and in bulk glass. Our calculations show that the presence of a dielectric interface, which coincides with the focal plane of a radially polarized laser beam, strongly changes the field intensity distribution within the focus, which results in the modification of the single molecule excitation pattern obtained upon scanning a molecule through the focal region. By changing the dielectric properties of the surrounding media in situ we show experimentally that the same individual molecule possessing the same orientation with respect to the laser beam axis exhibits different shapes of excitation patterns, depending on whether it is located on the dielectric interface or in medium with constant refractive index.