Generation of multiple focal holes by tightly focused azimuthally polarized double-ring-shaped beam with complex phase mask

We study the focusing properties of a tight focusing of double ring shaped azimuthally polarized beam through complex phase mask (CPM) with high NA objective lens, based on vector diffraction theory. A novel design to generate an azimuthally polarized subwavelength focal hole having FWHM of 0.332λ with long focal depth of about 18.8λ is illustrated numerically. Apart from generating focal hole with long focal depth, it is observed that a properly designed CPM also generates multiple focal hole segments useful for laser cutting, microscopy and the manipulation of optical traps of low refractive index particles.