Thursday, May 26, 2022

Converting invisible infrared into visible light

Color-changing magnifying glass gives a clear view of infrared light.

Infrared light carries so little energy compared to ambient heat at room temperature. This makes it difficult to detect light beyond the visible red range of our eyes.

Specialized detectors are needed for this task. These detectors are chilled to very low temperatures, both expensive and energy-intensive.

Scientists at the University of Cambridge have developed a new approach to detect infrared light. By trapping light into tiny crevices of gold, they have coaxed molecules to convert invisible infrared into visible light. Their concept of new low-cost detectors for sensing shows how to convert it into visible light, which is easily detected.

Scientists used a single layer of molecules to absorb the mid-infrared light inside their vibrating chemical bonds. These shaking molecules give their energy to the light they experience, ‘upconverting’ it to emissions closer to the blue end of the spectrum, which modern visible-light cameras can then detect.

First author Angelos Xomalis from Cambridge’s Cavendish Laboratory said, “We had to make sure the quaking molecules met the visible light quickly enough. This meant we had to trap light tightly around the molecules by squeezing it into crevices surrounded by gold.”

Scientists sandwiched single molecular layers between a mirror and tiny chunks of gold. They did this by using meta-materials that can twist and squeeze light into much smaller volumes.

Co-author Dr. Rohit Chikkaraddy from the Cavendish Laboratory, who devised the experiments based on his simulations of light in these building blocks, said, “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.”

Professor Jeremy Baumberg of the NanoPhotonics Centre at Cambridge’s Cavendish Laboratory, who led the research, said, “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.”

Scientists noted, “While it is early days, there are many ways to optimize the performance of these inexpensive molecular detectors, which then can access rich information in this window of the spectrum.”

This new detector can be used in astronomical observations of galactic structures, sensing human hormones, or early signs of invasive cancers. In simple words, many technologies can benefit from this new detector advance.

Journal Reference:

  1. Angelos Xomalis et al. ‘Detecting mid-infrared light by molecular frequency upconversion with dual-wavelength hybrid nanoantennas,’ Science (2021). DOI: 10.1126/science.abk2593

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