T-Ray Camera Speed Boosted a Hundredfold

An international research team led by professor Emma Pickwell-MacPherson from the University of Warwick has reached a crucial milestone toward developing single-pixel terahertz imaging technology for use in biomedical and industrial applications.

The single-pixel THz camera reached 100× faster acquisition than the previous state-of-the-art camera without adding significant costs to the entire system or sacrificing the subpicosecond temporal resolution necessary for the most sought-after applications.

Optical setup for single-pixel transmission imaging of object R. Courtesy of University of Warwick.

THz radiation is advantageous in numerous potential applications due to its nondestructive nature and its ability to see through many common materials such as plastics, ceramics, and clothes, and is highly sensitive to water and capable of observing minute changes to the hydration state of biological matter. Therefore, diseases perturbing the water content of biological matter such as skin cancer can potentially be detected using T-rays in vivo without histological markers. However, many barriers remain for the practical use of T-ray technology. Equipment is slow, costly, and not user-friendly.

Pickwell-MacPherson’s team uses a single-pixel camera to obtain its images, by spatially modulating the THz beam and shining its light onto an object. Then, with a single-element detector, the researchers record the light that is transmitted (or reflected) through the object, and continue to do so for many different spatial patterns until the image can be mathematically reconstructed.

Because the researchers have to continuously change the shape of the THz beam, the method is usually slower when compared to multipixel detector arrays. However, multipixel arrays for the THz regime usually lack subpicosecond temporal resolution, and they require cryogenic temperatures to operate or incur large equipment costs, which typically run around $350,000. The setup developed by the Warwick team is much cheaper, costing around $20,000; is robust with subpicosecond temporal resolution; 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 32 × 32 video at six frames per second,” Pickwell-MacPherson said. “We do this by firstly determining the optimal modulation geometry, secondly by modelizing 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.”

The researchers have previously developed several THz devices including THz modulators that make use of the total internal reflection geometry to achieve high MDs across a broadband frequency range, and a new approach for amplitude and phase modulation exploiting the Brewster angle. They are also working to improve the resolution of single-pixel THz imaging through signal processing approaches. Future work will focus on improving the signal-to-noise ratio and optimizing the software needed for accurate medical diagnosis, with the ultimate goal being to use single-pixel THz imaging for in vivo cancer diagnosis.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-020-16370-x).