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.