Super-resolution Imaging by Evanescent Wave Coupling to Surface States   on Effective Gain Media
  Higher resolution demands for semiconductor lithography may be fulfilled by higher numerical aperture (NA) systems. However, NAs more than the photoresist refractive index (~1.7) cause surface confinement of the image. In this letter we describe how evanescent wave coupling to effective gain medium surface states beneath the imaging layer can counter this problem. At {\lambda}=193 nm a layer of sapphire on SiO2 counters image decay by an effective-gain-medium resonance phenomena allowing evanescent interferometric lithography to create high aspect ratio structures at NAs of 1.85 (26-nm) and beyond. 
Prateek Mehrotra, Chris A. Mack, Richard J. Blaikie
physics.optics