Warwick leads breakthrough in terahertz imaging

The team’s single-pixel terahertz camera is said to have reached 100 times faster acquisition than the previous state-of-the-art without adding any significant costs to the system or forgoing the sub-picosecond temporal resolution needed for medical applications.

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The team, led by Prof. Emma Pickwell-Macpherson from Warwick University’s Department of Physics and involving Rayko Ivanov Stantchev and scientists from the The Chinese University of Hong Kong, have had their findings published in Nature Communications.

Terahertz (THz) radiation (T-rays) can see through materials including plastics, ceramics and clothes, making them potentially useful in non-invasive inspections. The low-energy photons of T-rays are non-ionising, making them very safe in biological settings such as security and medical screening.

THz technology is not, however, not widely used in commercial settings as the cost, robustness and ease of use is still lagging behind for commercial adoption.

For biomedical applications, very few clinical trials have been performed most notably due to the equipment not being user-friendly and imaging being too slow due to the need for measuring multiple terahertz frequencies for accurate diagnosis. Finally, equipment and running costs need to be within hospital budgets.

In a statement, Prof Emma Pickwell-Macpherson said: "We use what is called 'a single-pixel camera' to obtain our images. In short, we spatially modulate the THz beam and shine this light onto an object. Then, using a single-element detector, we record the light that is transmitted (or reflected) through the object we want to image. We keep doing this for many different spatial patterns until we can mathematically reconstruct an image of our object."

According to Warwick University, the researchers have to keep changing the shape of the THz beam many times which means this method is usually slower compared to multi-pixel detector arrays. However, multi-pixel arrays for the terahertz regime usually lack sub-picosecond temporal resolution, require cryogenic temperatures to operate or incur large equipment costs. The setup developed by the Warwick team, which is based on a single-element detector, costs around £16,000, is robust, has sub-picosecond temporal resolution required for accurate diagnosis, and operates at room temperature.

"Our latest work improves upon the acquisition rate of single-pixel terahertz cameras by a factor of 100 from the previous state-of-the-art, acquiring a 32x32 video at six frames-per-second,” said Prof Pickwell-Macpherson. “We do this by firstly determining the optimal modulation geometry, secondly by modelising the temporal response of our imaging system for improvement in signal-to-noise, and thirdly by reducing the total number of measurements with compressed sensing techniques. In fact, part of our work shows that we can reach a five times faster acquisition rate if we have sufficient signal-to-noise ratio."