MIRROR-DIFFRACTIVE OBJECTIVE LENS FOR FOCUSING RADIALLY POLARIZED LASER BEAM INTO ULTIMATELY SMALL SPOT
A new type of «dry» high aperture (NA ~ 1) mirror-diffractive objective lens is proposed and investigated. The objective lens has a large working distance (1 mm) and the internal transformation of the input radiation into a beam with annular aperture function. For radially polarized input radiation, the full width size of a laser spot evaluated at a half of central intensity maximum in the focal plane of the objective lens amounts to about 100 nm at the wavelength of 266 nm. The profile of the point spread function of the objective lens is close to the zero-order Bessel function of the first kind.