Abstract

We propose and demonstrate that a dark spot can be generated by a radially polarized beam with a first-order vortex after phase modulation by an optimal binary phase element. The distance between two mainlobe intensity peaks along the radial direction is $0.62\lambda$ on the focal plane. The proposed system is easy to implement in practice and has low energy loss, since it uses phase-only modulation. Then, the fluorescent spot is calculated for stimulated emission depletion microscopy when a radially polarized beam works as the pump beam. The FWHM of the fluorescent spot can achieve $0.008\lambda$ for a saturated case. This is much smaller than that achieved using a circular polarized vortex erase beam ($0.0422\lambda$) or an azimuthally polarized erase beam with optimizing amplitude-phase modulation ($0.0279\lambda$).

© 2017 Optical Society of America

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