  We demonstrate a conceptually new mechanism for sub-wavelength focusing at
optical frequencies based upon the use of nano-hole quasi-periodic arrays in
metal screens. Using coherent illumination at 660 nm and scanning near-field
optical microscopy, ~290 nm "hot spots", were observed at a distance of ~12.5
mkm from the array. Even smaller hot-spots of about 200 nm in waist were
observed closer to the plane of the array.
