Non-invasive, near-field terahertz imaging of hidden objects using a single pixel detector

TL;DR

This paper presents a novel near-field terahertz imaging technique using a single-pixel detector and optical masks, achieving subwavelength resolution for imaging concealed objects non-invasively.

Contribution

The work introduces a single-pixel, near-field THz imaging method with optical modulation, enabling high-resolution imaging of hidden objects through opaque materials.

Findings

Achieved ~100 μm resolution imaging through silicon.

Demonstrated detection of micron-scale fissures in circuitry.

Showcased potential applications in non-invasive concealed object imaging.

Abstract

Terahertz (THz) imaging has the ability to see through otherwise opaque materials. However, due to the long wavelengths of THz radiation ({\lambda}=300{\mu}m at 1THz), far-field THz imaging techniques are heavily outperformed by optical imaging in regards to the obtained resolution. In this work we demonstrate near-field THz imaging with a single-pixel detector. We project a time-varying optical mask onto a silicon wafer which is used to spatially modulate a pulse of THz radiation. The far-field transmission corresponding to each mask is recorded by a single element detector and this data is used to reconstruct the image of an object placed on the far side of the silicon wafer. We demonstrate a proof of principal application where we image a printed circuit board on the underside of a 115{\mu}m thick silicon wafer with ~100{\mu}m ({\lambda}/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity provided by the THz probe frequencies, we show that it is possible to detect fissures in the circuitry wiring of a few microns in size. Imaging systems of this type could have other uses where non-invasive measurement or imaging of concealed structures with high resolution is necessary, such as in semiconductor manufacturing or in bio-imaging.