Tapered photoconductive terahertz field probe tip with subwavelength spatial resolution

In this work a photoconductive probe tip applicable for near- and far-field measurements in the terahertz frequency regime is demonstrated as a powerful alternative to existing terahertz scanning near-field optical microscopy approaches. The probe tip is based on a triangular-shaped patch of freestanding low-temperature-grown GaAs of only 1.3 mu m thickness with a pair of tapered metallic wires on top. Using nonresonant electric field enhancement at the tip of the probing device, 10 mu m wide metallic structures are spatially resolved and a bandwidth of 2 THz is demonstrated.