Depolarization of evanescent waves scattered by laser-trapped gold particles: effect of particle size

Depolarization of evanescent waves scattered by laser-trapped gold particles of 0.1, 0.5 and 2 µm in diameter is experimentally characterized in order to reveal its dependence on the size of particles. It is found that the degree of polarization of scattered evanescent waves decreases with the size of gold particles, which is contrary to that previously observed for dielectric particles. This feature becomes advantageous in particle-trapped near-field microscopy since less depolarized photons carry more information of a sample. With the help of polarization gating, this property is demonstrated in images of the evanescent wave interference pattern as well as the surface of a glass prism.