Direct Near-field Imaging of UV Surface Plasmon of a Bowtie Optical Nano-antenna

Study of Ultraviolet Surface Plasmon Polariton (SPP) is of special interest because of UV light's wide applications. Near-field Scanning Microscopy (NSOM) has been proven to be one of the most effective ways of characterizing SPP modes thanks to its highly localized signal collection from surface with a sub-wavelength resolution. A resolution of 60nm is achieved on our NSOM which is capable of working with deep-UV (down to 244nm) light. By utilizing this NSOM working under collection mode, we directly imaged the UV SPP modes on various nanostructures on an Al/Al2O3 thin film, among which a bowtie antenna structure showed extraordinary quality of both confining UV light field to a sub-wavelength size and enhancing the optical intensity as well. Numerical simulation of said structure is also reported and discussed, revealing that a bowtie antenna is a promising candidate for many uses such as a novel NSOM tip, optical sensors and optical nano-trap etc.