Tight focusing with a binary microaxicon

Using a near-field scanning microscope (NT-MDT) with a 100nm aperture cantilever held 1 μm apart from a micro-axicon of diameter 14 μm and period 800nm, we measure a focal spot resulting from the illumination by a linearly polarized laser light of wavelength λ 532nm, with its FWHMbeing equal to 0:58λ, and the depth of focus being 5:6λ. The rms deviation of the focal spot intensity from the calculated value is 6%. The focus intensity is five times larger than the maximal illumination beam intensity. © 2011 Optical Society of America OCIS codes: 050.1380, 180.4243. Axicons are known to be suitable for generating a diffraction-free laser Bessel beam at a certain optical axis segment. Despite being widely known in optics for quite some time, interest in axicons has not weakened. Surface plasmons with a sharp central peak were generated in metal films by use of an axicon in Refs. [1,2]. A binary axicon of period 33 μm was studied in Ref. [3]. The minimal diameter of the laser beam was 1:2 μm (at wave-length λ 532 nm). The laser beam diameter was show