Tight focusing induced non-uniform polarization change in reflection for arbitrarily polarized incident light

Abstract

Tight focusing of light through a high numerical aperture (NA) objective can produce a subwavelength focal spot and this technique has thus been widely applied in many microscopic systems. Here we show that the polarization of the light reflected from a high-NA objective shows a significant change when compared with that of the incident light, which would be crucial in polarization-dependent imaging and detection applications. Some typical polarized incident light beams, including linearly, circularly, and elliptically polarized light beams and cylindrical vector beams, are studied both theoretically and experimentally. We find that with the exception of pure radial and azimuthal polarizations, all other polarizations of the incident light show nonuniform changes in the reflected light, particularly in the total internal reflection region. We build a theoretical model of the observed polarization change effect and experimentally verify that this model is valid for use with arbitrarily polarized light. This work could contribute to the design of various high-NA microscopic systems, including those intended for polarization-dependent imaging, and polarization differential sensing applications.