Subwavelength and super-resolution nondiffraction beam

A light spot that is smaller than a half wavelength will subsequently diverge in all directions. In this letter, the authors model a subwavelength (0.42λ) super-resolution light beam which propagates over a long distance without any divergence. This can be achieved by placing a multibelt pure-phase-type binary optical element on the lens pupil. The authors also report a useful approach for designing the optical element, based on vector diffraction theory, which can be used in paraxial and nonparaxial focusing and imaging systems.