Improvement of Focusing Characteristics of a Spiral Plasmonic Lens

We designed and fabricated a spiral plasmonic lens (PL) with multi-circular grooves to increase light intensity in a far-field region via the constructive interference of the light scattered by the multi-circular grooves. To compare the beam focusing characteristics of a spiral PL with multi-circular grooves with those of a conventional spiral PL, we simulated the electric field distribution of the PLs operating at a 405 nm wavelength. We confirmed that the light intensity increased about twofold at 0.75 mu m above the PL surface owing to the effect of the multi-circular grooves. Furthermore, the circular grooves negligibly affect the full width at half-maximum of the focal spot, keeping the subwavelength size (similar to 200 nm) of incident light. (C) 2014 The Japan Society of Applied Physics