High efficiency near-field electromagnetic probe having a bowtie antenna structure

TLDR: In this paper, a near field electromagnetic probe converts an incident energy beam into an interrogating beam which exhibits, in the near field vicinity of the probe, a transverse dimension that is small in relation to the wavelength of the energy beam.

Abstract: A near field electromagnetic probe converts an incident energy beam into an interrogating beam which exhibits, in the near field vicinity of the probe, a transverse dimension that is small in relation to the wavelength of the incident energy beam The probe comprises an energy source for providing the incident energy beam with a wavelength λ An antenna is positioned in the path of the incident energy beam and comprises at least a first conductive region and a second conductive region, both of which have output ends that are electrically separated by a gap whose lateral dimension is substantially less than λ The electromagnetic system which produces the incident energy should preferably have its numerical aperture matched to the far-field beam pattern of the antenna Further, the incident beam should have a direction of polarization which matches the preferred polarization of the antenna The near field probe system of the invention can also sense fields in the near field gap and reradiate these to a far-field optical detector Thus the probe can serve to both illuminate a sample in the near field gap, and to collect optical signals from an illuminated sample in the near field gap