Elongating the Air Working Distance of Near-Field Plasmonic Lens by Surface Plasmon Illumination

Abstract

A method is proposed and demonstrated to elongate the air working distance of near-field plasmonic lens with deep subwavelength resolution. It is done by employing surface plasmon illumination (SPI) with a high transverse wavevector and a plasmonic lens with a metal-dielectric-metal structure. Specially designed SPI source with subwavelength grating and multiple metal-dielectric films delivers the shifted spatial spectra components of mask patterns, which help to enhance plasmonic lens optical transfer ability of patterns’ information even with a large air working distance. Moreover, a metal reflector serves to modulate the magnitude of the tangential and normal electric field components in the imaging region and brings the considerable improvement of imaging quality. Numerical simulations show that the maximum air working distance could reach 60 for 32 nm half-pitch resolution at 365 nm wavelength about six times that for the conventional superlens under normal illumination (NI). An approximate model of the air working distance elongation under SPI is given and agrees well with simulations.