Evanescent light can be localized at the nanoscale by resonant absorption in a plasmonic nanoparticle or taper or by transmission through a nanohole.However,a conventional lens cannot focus free-space light beyond hal...Evanescent light can be localized at the nanoscale by resonant absorption in a plasmonic nanoparticle or taper or by transmission through a nanohole.However,a conventional lens cannot focus free-space light beyond half of the wavelength λ.Nevertheless,precisely tailored interference of multiple waves can form a hotspot in free space of an arbitrarily small size,which is known as superoscillation.Here,we report a new type of integrated metasurface interferometry that allows for the first time mapping of fields with a deep subwavelength resolution ~λ/100.The findings reveal that an electromagnetic field near the superoscillatory hotspot has many features similar to those found near resonant plasmonic nanoparticles or nanoholes:the hotspots are surrounded by nanoscale phase singularities and zones where the phase of the superoscillatory field changes more than tenfold faster than a freepropagating plane wave.Areas with high local wavevectors are pinned to phase vortices and zones of energy backflow(~λ/20 in size)that contribute to tightening of the main focal spot size beyond the Abbe-Rayleigh limit.Our observations reveal some analogy between plasmonic nanofocusing of evanescent waves and superoscillatory nanofocusing of free-space waves and prove the fundamental link between superoscillations and superfocusing,offering new opportunities for nanoscale metrology and imaging.展开更多
基金supported by the Singapore Ministry of Education(Grant MOE2011-T3-1-005)ASTAR QTE Program Grant SERC A1685b0005the Engineering and Physical Sciences Research Council UK(Grant EP/G060363/1).
文摘Evanescent light can be localized at the nanoscale by resonant absorption in a plasmonic nanoparticle or taper or by transmission through a nanohole.However,a conventional lens cannot focus free-space light beyond half of the wavelength λ.Nevertheless,precisely tailored interference of multiple waves can form a hotspot in free space of an arbitrarily small size,which is known as superoscillation.Here,we report a new type of integrated metasurface interferometry that allows for the first time mapping of fields with a deep subwavelength resolution ~λ/100.The findings reveal that an electromagnetic field near the superoscillatory hotspot has many features similar to those found near resonant plasmonic nanoparticles or nanoholes:the hotspots are surrounded by nanoscale phase singularities and zones where the phase of the superoscillatory field changes more than tenfold faster than a freepropagating plane wave.Areas with high local wavevectors are pinned to phase vortices and zones of energy backflow(~λ/20 in size)that contribute to tightening of the main focal spot size beyond the Abbe-Rayleigh limit.Our observations reveal some analogy between plasmonic nanofocusing of evanescent waves and superoscillatory nanofocusing of free-space waves and prove the fundamental link between superoscillations and superfocusing,offering new opportunities for nanoscale metrology and imaging.
