Imaging through planar silver lenses in the optical near field

Near-field imaging through planar silver lenses has been demonstrated using a modified conformal-mask optical lithography arrangement. Dense feature resolution down to 250 nm (on a 500 nm period) has been achieved in 50 nm thick photoresist on silicon using broadband illumination from a mercury lamp. Finite difference time domain simulations have been performed to show the resolution improvements that can be expected for imaging through such silver lenses compared with near-field proximity imaging. The resolution enhancements that are predicted are in good agreement with the experimental results, and the conditions by which sub-diffraction-limited resolution may be achieved are given.