Dependence of strength and depolarization of scattered evanescent waves on the size of laser-trapped dielectric particles

Scattered evanescent waves are characterized experimentally with laser-trapped dielectric particles of different sizes in order to improve image quality in particle-trapped near-field scanning microscopy. It is found that although the strength of scattered evanescent waves increases monotonically with the size of a laser-trapped particle, image contrast of an evanescent wave interference pattern exhibits a maximum value for an intermediate-sized particle. In addition, it is found that the degree of polarization of scattered evanescent waves increases with the size of a laser-trapped particle. The depolarization effect is more significant for s polarized light than p polarized light for a large-sized particle, while this tendency reverses for a particle of small size.