Sharper fluorescent super-resolution spot generated by azimuthally polarized beam in STED microscopy

A novel method is proposed for generating sharper fluorescent super-resolution spot by azimuthally polarized beam in stimulated emission depletion (STED) microscopy. The incoherent superposition of azimuthally polarized beam with five-zone binary phase plate and the same beam with quadrant 0/pi phase plate can yield a tightly focused doughnut spot surrounded completely and uniformly. And azimuthally polarized beam modulated by a vortex 0-2 pi phase plate works as pump beam. Compared with known effective excitation spot yielded by circular polarized STED beam, the azimuthally polarized beam result is shaper, as well as energy-saving, costing only similar to 50% of the energy cost by circular polarized beam. A STED beam of less intensity has the potential to reduce fluorescence photobleaching and photodamage in living cell imaging. In addition, the influence of E-z absence as well as FWHM of pump beam in the focal field is discussed. (C) 2012 Optical Society of America