title: Spot-size reduction in terahertz apertureless near-field imaging.
abstract: We show measurements and calculations of the terahertz (THz) near field of a metal tip with a specially formed, semicircular apex that allows us to identify the separate contributions of the tip apex and shaft to the measured signal. We find that when the tip-crystal distance is not modulated the measured near-field signal is overwhelmed by contributions from the tip shaft, resulting in a relatively large THz spot size. When the tip-crystal distance is modulated, with subsequent lock-in detection at the modulation frequency, only the near-field distribution of the semicircular apex is observed, resulting in a much smaller THz spot size and thus improved spatial resolution.
authors.affiliation: Faculty of Applied Sciences, University of Technology Delft, Delft, The Netherlands. p.c.m.planken@tnw.tudelft.nl
authors.forename: P C M
authors.initials: PC
authors.lastname: Planken
authors.forename: N C J
authors.initials: NC
authors.lastname: van der Valk