THz nanofocusing with cantilevered THz-resonant antenna tips

TL;DR

This paper introduces THz-resonant AFM tips that significantly enhance and confine THz near fields at the nanoscale, enabling advanced applications in THz nanoscopy and nonlinear imaging.

Contribution

Development of THz-resonant scanning probe tips with geometrical antenna resonances, achieving strong near-field enhancement at the nanoscale.

Findings

Near-field intensity enhanced by one order of magnitude at resonance

Numerical simulations predict intensity enhancements of about 10^7

Resonant tips enable potential applications in THz nanoscopy

Abstract

We developed THz-resonant scanning probe tips, yielding strongly enhanced and nanoscale confined THz near fields at their tip apex. The tips with length in the order of the THz wavelength ({\lambda} = 96.5 {\mu}m) were fabricated by focused ion beam (FIB) machining and attached to standard atomic force microscopy (AFM) cantilevers. Measurements of the near-field intensity at the very tip apex (25 nm radius) as a function of tip length, via graphene-based (thermoelectric) near-field detection, indicate their first and second order geometrical antenna resonances for tip length of 33 and 78 {\mu}m, respectively. On resonance, we find that the near-field intensity is enhanced by one order of magnitude compared to tips of 17 {\mu}m length (standard AFM tip length), which is corroborated by numerical simulations that further predict remarkable intensity enhancements of about 107 relative to the incident field. Because of the strong field enhancement and standard AFM operation of our tips, we envision manifold and straightforward future application in scattering-type THz near-field nanoscopy and THz photocurrent nanoimaging, nanoscale nonlinear THz imaging, or nanoscale control and manipulation of matter employing ultrastrong and ultrashort THz pulses.