Focusing Radially Polarized Light by a Concentrically Corrugated Silver Film without a Hole

Wróbel P., Pniewski J., Antosiewicz T.J., and Szoplik T.

Physical Review Letters

102, 2009, art. 183902, 10.1103/PhysRevLett.102.183902

We report a phenomenon of focusing a radially polarized beam from the visible range by a silver film with no hole on the optical axis and double-sided concentric corrugations. The axes of symmetry of grooves and the illuminating beam coincide. An Ag lens of 100 nm thickness, five grooves, of which the outermost has 5  μm diameter, at λ=400  nm transmits 22% of electric energy and focuses light into a 0.2λ2 spot area at a focal length close to 2λ, while at λ=500  nm the results are 11%, 0.16λ2 and λ, respectively. This Ag lens focuses without contribution of evanescent waves a far-field source into a far-field spot. The nanolens acts like a refractive optical system of high numerical aperture close to unity.