Terahertz wave camera images the microscopic world

Scientists at Loughborough University have demonstrated that a terahertz wave camera can capture 3D images of microscopic items hidden inside small objects, in what is reported to be a world first.

Their research, which included experts from Loughborough’s Emergent Photonics Research Centre (EPicX), demonstrates that terahertz waves can be used to locate and recognise embedded objects and features, such as cracks and bubbles, in microscopic three-dimensional space. It has been published in the journal ACS Photonics.

Terahertz waves are a vastly unexplored part of the electromagnetic spectrum with frequencies ranging between microwave and infrared light. They have several properties that make them extremely useful, such as their ability to penetrate opaque objects without causing harm. However, one of the problems in the field of terahertz imaging is the limited ability to view microscopic objects.

Lead researcher Dr Luana Olivieri and the EPicX team have overcome this limitation by developing an approach known as ‘time-resolved nonlinear ghost imaging’, which combines a range of advanced detection methods and involves manipulating light and measuring how it travels through an object over time. Their method allows smaller objects to be seen more clearly, though it was previously only proven to work on 2D objects.

In their latest study, the researchers proved the technique can capture 3D images of microscopic items by probing 4 mm x 4 mm x 600 µm cubes with terahertz radiation. The imaging technique allowed them to separate and distinguish information from different depths and create detailed, 3D images of the cubes with high accuracy — allowing them to observe the chemical and physical nature of items inside them in a way that was not possible before.

Olivieri and team were able to see features hidden inside the cubes as small as 60 µm, which is roughly the width of a human hair. While this might not seem very small, usually terahertz waves can only identify objects around 300 µm or larger, which was the reason terahertz was previously precluded from microscopy.

“This new approach is enabling because it allows us to see things that are too small or too obscured to be within reach of traditional methods,” Olivieri said.

“Reading the story of how light has travelled through an object is often a complex task, but with this process, we can retrieve the information encrypted, unravelling the multidimensional data to unveil hidden and ‘invisible’ objects at the microscale.

“Most importantly, terahertz allows us to see through objects that are not transparent with visible light and produce 3D images.”

Although the research is in the early stages, Olivieri said it could have major implications for a range of fields, with examples provided by fellow researcher Dr Luke Peters.

“In medicine, terahertz imaging could be used to detect and diagnose skin cancers that are not visible to the naked eye,” Peters said.

“In security, it could be used to improve the resolution of scanners that are used to search people for concealed weapons or explosives, without the need for physical pat-downs or intrusive searches.

“And in materials science, terahertz imaging could be used to study the properties of new materials and identify defects or impurities that may affect their performance.

“Our work allows us to expand these capabilities into the microscopic domain.”

Image caption: Microscopic, metallic objects distributed throughout a 3D cube. Metallic objects were imaged using the terahertz wave camera and then combined with an artistic, rendered image.