Focusing of Light by a Nano-Hole Array

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.