Real-Time Analysis of THz Quantum-Cascade Laser Signals using a Field Effect Transistor Array

We demonstrate real-time analysis of the emission from a 3.4-THz quantum-cascade laser (QCL) source, using an array of nanoscale field-effect transistor devices. We show that THz power can be detected directly up to a modulation bandwidth of 500 kHz, and indirectly via a change in the device threshold, up to a 100-MHz bandwidth.

I. Introduction

TERAHERTZ-FREQUENCY quantum-cascade lasers (THz QCLs) are compact semiconductor sources of narrowband radiation in the -THz band. They have been shown to allow high direct-modulation bandwidths, up to >35 GHz [1], potentially underpinning their applications in high-speed wireless communications, real-time gas sensing, or industrial inspection. For example, numerous important atmospheric gasphase species have strong spectral features in the THz band (e.g., atomic oxygen at -THz), and fast tunable-laser spectroscopy techniques could be used to analyze their reaction kinetics on nanosecond-scale timescales. However, fast analysis of THz QCL signals typically requires either complex heterodyne techniques, or cryogenic detectors. THz field-effect transistor (TeraFET) detectors have recently been shown to offer low-noise room-temperature detection of THz QCL signals over kHz bandwidths [2], but the use of a single-element detector with a patch-antenna introduces very high sensitivity to system alignment.