Sussex team make EPic breakthrough with THz radiation

Physicists have developed what they say is the first nonlinear camera that captures high-resolution images of the interior of solid objects using terahertz (THz) radiation.

Artistic rendering of the terahertz field transmitted by an abstract object (Image: Sussex University)

The breakthrough at Sussex University was led by Professor Marco Peccianti of the Emergent Photonics (EPic) Lab and included Luana Olivieri, Dr Juan S. Totero Gongora and a team of research students.

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According to the university, images produced with THz radiation are called 'hyperspectral' because the image consists of pixels, each one containing the electromagnetic signature of the object in that point. Lying between microwaves and infrared in the electromagnetic spectrum, THz radiation easily penetrates materials like paper, clothes and plastic in the same way X-rays do, but without being harmful. THz radiation is safe to use with biological samples and makes it possible to visualise the molecular composition of objects and distinguish between different materials.

"The core challenge in THz cameras is not about collecting an image, but it is about preserving the objects spectral fingerprint that can be easily corrupted by your technique,” Prof Peccianti said in a statement. “This is where the importance of our achievement lies. The fingerprint of all the details of the image is preserved in such a way that we can investigate the nature of the object in full detail."

The EPic Lab team used a single-pixel camera to image sample objects with patterns of THz light. Their prototype can detect how the object alters different patterns of THz light. By combining this information with the shape of each original pattern, the camera reveals the image of an object as well as its chemical composition.

THz radiation
The time-resolved nonlinear ghost imaging camera uses a nonlinear crystal to convert standard laser light to terahertz patterns, allowing the reconstruction of complex samples using a single terahertz pixel (Image Sussex University)

Sources of THz radiation are very faint and hyperspectral imaging had, until now, limited fidelity. To overcome this, The Sussex team shone a standard laser onto a unique non-linear material capable of converting visible light to THz. The prototype camera creates THz electromagnetic waves very close to the sample, similar to how a microscope works. As THz waves can travel right through an object without affecting it, the resulting images reveal the shape and composition of objects in three dimensions.

Dr Totero Gongora said: "This is a major step forward because we have demonstrated that all the possibilities explored in our previous theoretical research are not only feasible, but our camera works even better than we expected. While building our device, we discovered several ways to optimise the imaging process and now the technology is stable and works well. The next phase of our research will be in speeding up the image reconstruction process and taking us closer to applying THz cameras to real-world applications; like airport security, intelligent car sensors, quality control in manufacturing and even scanners to detect health problems like skin cancer."

Hyperspectral terahertz microscopy via nonlinear ghost-imaging is published in the OSA Optica Journal.