Tight focusing of the azimuthally polarized light beam for a sharper spot

•We proposed a beam shape system that combines pupil filter and high-NA lens.•The azimuthally polarized focal spot size is smaller than other polarized beams.•Compared to system with annular aperture, the minimum FWHM is improved to 0.259λ.•The energy efficiency of focal spot in our proposed method always exceeds 10%.•The impact of different binary-phase optical elements on focusing is discussed.

This paper presents a method to focus azimuthally polarized vortex light beam by the combination of a vortex phase plate, a binary-phase optical element (BOE) and a high-numerical aperture (NA) objective lens. Our proposed method achieves a smaller spot size than other polarized beams under the same condition. Compared to the system with the annular aperture, the minimum of full width at half-maximum is improved to 0.259λ and the energy conversion efficiency is higher in the proposed method when FWHM <0.284λ. The Strehl Ratio of the focused spot always exceeds 10%. The impact of changing the BOE׳s structure and parameters on focusing results is also discussed.