Detecting light beyond the visible red range of our eyes is hard to do, because infrared light carries so little energy compared to ambient heat at room tempera­ture. This obscures infrared light unless specialised detectors are chilled to very low tempera­tures, which is both expensive and energy-intensive. Now, researchers led by the University of Cambridge have demons­trated a new concept in detecting infrared light, showing how to convert it into visible light, which is easily detected.

In colla­boration with colleagues from the UK, Spain and Belgium, the team used a single layer of molecules to absorb the mid-infrared light inside their vibrating chemical bonds. These shaking molecules can donate their energy to visible light that they encounter, upcon­verting it to emissions closer to the blue end of the spectrum, which can then be detected by modern visible-light cameras. The results open up new low-cost ways to sense contaminants, track cancers, check gas mixtures, and remotely sense the outer universe.

The challenge faced by the researchers was to make sure the quaking molecules met the visible light quickly enough. “This meant we had to trap light really tightly around the molecules, by squeezing it into crevices surrounded by gold,” said Angelos Xomalis from Cambridge’s Caven­dish Labora­tory. The researchers devised a way to sandwich single molecular layers between a mirror and tiny chunks of gold, only possible with meta­materials that can twist and squeeze light into volumes a billion times smaller than a human hair.

“Trapping these different colors of light at the same time was hard, but we wanted to find a way that wouldn’t be expensive and could easily produce practical devices,” said Rohit Chikka­raddy from the Cavendish Labora­tory, who devised the experiments based on his simulations of light in these building blocks. “It’s like listening to slow-rippling earth­quake waves by colliding them with a violin string to get a high whistle that’s easy to hear, and without breaking the violin,” said Jeremy Baumberg of the Nano­Photonics Centre at Cambridge’s Cavendish Laboratory, who led the research. 

The researchers emphasise that while it is early days, there are many ways to optimise the per­formance of these inex­pensive molecular detectors, which then can access rich information in this window of the spectrum. From astro­nomical obser­vations of galactic structures to sensing human hormones or early signs of invasive cancers, many technologies can benefit from this new detector advance. The research was conducted by a team from the University of Cambridge, KU Leuven, University College London (UCL), the Faraday Insti­tution, and Universitat Politècnica de València. (Source: U. Cambridge)

Reference: A. Xomalis et al.: Detecting mid-infrared light by molecular frequency upconversion in dual-wavelength nanoantennas, Science 374, 1268 (2021); DOI: 10.1126/science.abk2593

Link: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge, Cambridge, UK