Metacoatings for wavelength scale, high NA plano-concave focusing lenses
  We design plano-concave silicon lenses with coupled gradient-index plasmonic metacoatings for ultrawide apertured focusing utilizing a reduced region of $\sim 20 \lambda^2$. The anomalous refraction induced in the planar input side of the lens and in the boundary of the wavelength-scale focal region boosts the curvature of the emerging wavefront, thus significantly enhancing the resolution of the tightly-focused optical wave. The formation of a light tongue with dimensions approaching those of the concave opening is here evidenced. This scheme is expected to have potential applications in optical trapping and detection. 
Mahin Naserpour and Carlos J. Zapata-Rodr\'iguez and Carlos   D\'iaz-Avi\~n\'o and Mahdieh Hashemi
physics.optics