| In this work, we show our proof-of-concept experiments demonstrating that plasmonics and optical metamaterials can offer unique enhancements to the diffraction properties of metallic nanoslits lenses. In these experiments we have designed focusing devices that employ arrays of nanoscale slits fabricated in metallic films. First we show that, depending on the incident linear polarization, our plasmonic diffractive focusing devices perform similarly to conventional dielectric convex or concave lenses. Then, through the use of optical experiments and numerical simulations, we demonstrate that the focal intensity of our nanoslit lenses can be tuned. This can be accomplished if the slits are filled with liquid crystals, for example. We also show that the diffraction pattern of a double-slit mask can have subwavelength features, provided that the diffraction peaks are formed inside a metamaterial with hyperbolic dispersion. The planar, compact, nanoslit lenses that we have studied could be useful in a number of applications such as subwavelength probes, subwavelength lithography and sensing. Finally, we discuss in detail the dielectric properties of the plasmonic materials used in each of our nanoslit lenses with an eye toward improving the operation of the plasmonic devices by selecting appropriate and perhaps nontraditional plasmonic constituent materials. |
