Detectorless 3D terahertz imaging: achieving subwavelength resolution with reflectance confocal interferometric microscopy

TL;DR

This paper introduces a novel single-pixel terahertz imaging system with confocal interferometric microscopy that achieves subwavelength resolution and rapid 3D imaging, surpassing traditional methods for material inspection.

Contribution

The study presents a detectorless THz imaging approach using a quantum cascade laser and phase-sensitive detection to significantly improve resolution and imaging speed over existing systems.

Findings

Achieves near λ/2 lateral resolution and better than λ/5 depth of focus.

Produces 0.5 Megapixel images in under two minutes.

Demonstrates subwavelength 3D imaging of a silicon chip.

Abstract

Terahertz imaging holds great potential for non-destructive material inspection, but practical implementation has been limited by resolution constraints. In this study, we present a single-pixel THz imaging system based on a confocal microscope architecture, utilising a quantum cascade laser as both transmitter and phase-sensitive receiver. Our approach integrates laser feedback interferometry detection to achieve a two-fold improvement in lateral resolution and a two-order-of-magnitude enhancement in axial resolution over conventional imaging through precise interferometric phase measurements. This translates to a lateral resolution near $\lambda/2$ and a depth of focus better than $\lambda/5$, significantly outperforming traditional confocal systems. The system can produce a 0.5 Mpixel image in under two minutes, surpassing both raster-scanning single-pixel and multipixel focal-plane array-based imagers. Coherent operation enables simultaneous amplitude and phase image acquisition, and a custom visualisation method links amplitude to image saturation and phase to hue, enhancing material characterisation. A 3D tomographic analysis of a silicon chip reveals subwavelength features, demonstrating the system's potential for high-resolution THz imaging and material analysis. This work sets a new benchmark for THz imaging, overcoming key challenges and opening up transformative possibilities for non-destructive material inspection and characterisation.