Tight focusing of phase modulated double ring shaped radially polarized beam with high NA lens

Abstract

Based on the vector diffraction theory, the effect of phase modulation on the intensity distribution of double ring shaped radially polarized beam(R-TEM11*) in the focal region of high NA lens is investigated theoretically. It is observed that a properly designed complex phase filter can generate a sub wavelength focal spot having FWHM of 0.3λ with an extended focal depth of 10λ. Apart from generating focal spot segment with large focal depth, it is also observed that a properly designed complex phase filter also generate optical cage, multiple focal spot segment useful for the manipulation of optical trapping.