Experimental verification on tightly focused radially polarized vortex beams
Du Fu-Rong (杜富荣)a, Zhou Zhe-Hai (周哲海)a, Tan Qiao-Feng (谭峭峰)b, Yang Chang-Xi (杨昌喜)b, Zhang Xiao-Qing (张晓青)a, Zhu Lian-Qing (祝连庆)a
a Beijing Engineering Research Center of Optoelectronic Information and Instruments, Beijing Information Science and Technology University, Beijing 100192, China; b State Key Laboratory of Precision Measurement Technology and Instruments, Tsinghua University, Beijing 100084, China
Abstract The theoretical and experimental results of tightly focused radially polarized vortex beams are demonstrated. An auto-focus technology is introduced into the measurement system in order to enhance the measurement precision, and the radially polarized vortex beams are generated by a liquid-crystal polarization converter and a vortex phase plate. The focused fields of radially polarized vortex beams with different topological charges at numerical apertures (NAs) of 0.65 and 0.85 are measured respectively, and the results indicate that the total intensity distribution at focus is dependent not only on the NA of the focusing objective lens and polarization pattern of the beam but also on the topological charge l of the beam. Some unique focusing properties of radially polarized vortex beams with fractional topological charges are presented based on numerical calculations. The experimental verification paves the way for some practical applications of radially polarized vortex beams, such as in optical trapping, near-field microscopy, and material processing.
(Beam characteristics: profile, intensity, and power; spatial pattern formation)
Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 61108047 and 60908015) and the Beijing Excellent Talent Training Project, China (Grant No. 2011D005007000008).
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