Continuous-wave coherent imaging with terahertz quantum cascade lasers using electro-optic harmonic sampling

TL;DR

This paper presents a coherent imaging system using a phase-locked terahertz quantum cascade laser and electro-optic sampling, achieving high stability and low noise for imaging at 2.5 THz.

Contribution

The work introduces a novel phase-locked THz QCL system with electro-optic sampling for coherent imaging, demonstrating improved stability and noise performance.

Findings

Detection noise floor of 3 pW/Hz

Long-term phase stability of <3 degrees/hour

Successful raster scan imaging at 2.5 THz

Abstract

We demonstrate a coherent imaging system based on a terahertz (THz) frequency quantum cascade laser (QCL) phase-locked to a near-infrared fs-laser comb. The phase locking enables coherent electro-optic sampling of the continuous-wave radiation emitted by the QCL through the generation of a heterodyne beat-note signal. We use this beat-note signal to demonstrate raster scan coherent imaging using a QCL emitting at 2.5 THz. At this frequency the detection noise floor of our system is of 3 pW/Hz and the long-term phase stability is <3 degrees/h, limited by the mechanical stability of the apparatus.