Experimental research on the longitudinal field generated by a tightly focused beam

The longitudinal optical field is a peculiar physical phenomenon which is always involved with the domain of near-field optics. Due to its extraordinary properties, recently, it attracts increasing attention in research and application. In this work, the longitudinal fields generated by the evanescent illumination of tightly focused different polarized hollow beams are investigated. The focused light fields are numerically simulated according to the vector diffraction theory and their vector analysis is also carried out. And the longitudinal fields on the focal plane are demonstrated experimentally using a tip-enhanced scanning near-field microscopy. The simulation and experimental results show that the tightly focused radially polarized beam is suited to generate a stronger and purer longitudinal optical field at the focus.