Depolarization effect in light scattering of a single gold nanosphere

It is generally believed that the depolarization effect in light scattering of a nanostructure is mainly caused by its anisotropy, and in the case of an isotropic structure, e.g. a nanosphere, the depolarized signal will be too weak to be detected. In this work, we experimentally demonstrate that even a totally symmetric Au nanosphere exhibits sophisticated depolarization effects. The scattering image is not only dependent on the detailed excitation-observation polarization configuration but also related to the numerical aperture of the observation system. The depolarization effect of a single gold nanosphere was also confirmed with a reflective polarized light microscope. This is contrary to the commonly used image interpretation theory in polarized light microscopy that the image contrast is solely caused by the anisotropy of the sample.