Photoconductive terahertz near-field detectors for operation with 1550-nm pulsed friber lasers

We present a new generation of photoconductive (PC) terahertz (THz) near-field probes based on freestanding Beryllium-doped low-temperature-grown InGaAs/InAlAs cantilevers. The PC probes are compatible to optical gating with a femtosecond laser having a center wavelength of 1550 nm. Therefore, they are well suited for a cost-efficient direct integration with fiber-coupled THz time-domain spectroscopy (TDS) systems. The photoconductor material features electron lifetimes of 500 fs allowing for broadband detection up to 2 THz, which is comparable to existing LT-GaAs-based near-field detectors, which require 800-nm wavelength excitation. We demonstrate the detector operation in a state-of-the-art fiber-based TDS system with fast and coherent data acquisition and show obtained sheet-resistance mappings of conductive thin-films featuring subwavelength resolution.