Image enhancement for flat and rough film plasmon superlenses by adding loss

Abstract

Though surface plasmon resonances can reduce image beam width of a plasmon superlens, they distort the transfer function in the spectrum and introduce large image sidelobes as well. In this paper, image enhancement of a plasmon film superlens is investigated by adding permittivity loss. First, we add the loss in the film of the superlens and observe the sidelobes suppression. Second, we introduce loss in the image region of the superlens device and observe a flatter transfer function and obtain improved image resolution. For the silver film superlens at a free space wavelength of 337.5 nm, a beam width reduction of 69% is observed. Previously, we found that introducing roughness in the superlens can reduce the beam width. In this paper, we combine surface roughness with the method of adding loss in the image region and observe a further beam width reduction. The lossy sinusoidal surface superlens at a wavelength of 351 nm gains a beam width reduction of 86% compared to the lossless flat superlens. Moreover, in this paper we provide a model for calculating the superlens near-field image intensity when the objects are illuminated by a laser source, and the more general five slits example is shown to further demonstrate the advantage of adding loss.