Polarization of focal spot for high numerical aperture radially polarized beam

Abstract

According to Wolf and Richards vectorial diffraction theory, an electric field intensity model of focal spot for high numerical aperture radially polarized beam is established to analyze the intensity distributions of the focal spot and the polarization components of the electric field along the x, y and z axis, separately. In the reflection-mode confocal of imaging system, the intensity distributions of focal spot is obtained utilizing the gold nanoparticles, and the intensity distributions of the polarization components of the electric field along the x, y and z axis are obtained utilizing the gold nanorods. In the incident light, the polarization component along the z axis is nonexistent in front of the objective. But there is the polarization component along the z axis, which is relative to the numerical aperture, in the focal spot behind the objective. When the numerical aperture increases from 0.8 to 1.4, the ratio of the polarization component maximum along the z axis to that along the x axis or y axis increases from 0.57 to 3.16. The results show that the focal spot of radially polarized beam through high numerical aperture objective have the polarization component along the x, y and z axis, separately, and polarization component along z axis is much more than the other.