Purdue University researchers have achieved a significant breakthrough in the science of thermal radiation by discovering a novel approach for creating spinning thermal radiation in a controlled and efficient manner utilising artificially designed surfaces known as metasurfaces. The results were published in the journal Science Advances under the title “Observation of non-vanishing optical helicity in heat radiation from symmetry-broken metasurfaces,” headed by Zubin Jacob, Elmore Associate Professor of Electrical and Computer Engineering at Purdue.
Thermal radiation, which is caused by random oscillations in materials, has long been regarded as an incoherent signal. The radiated heat from most common thermal emitters has little or no circular polarisation. Surprisingly, many celestial objects’ thermal radiation reaching Earth has considerable circular polarisation. This remarkable phenomena leads to the finding of high magnetic fields in certain condensed stars, gives solutions for early cosmos mysteries, and even provides a probable signal of life.
“In nature, spinning thermal radiation is incredibly uncommon and only observed in a few condensed stars,” Jacob said. “Our research demonstrates a novel method for producing this sort of radiation, which has the potential to be employed in a wide range of applications, including thermal imaging and communication.”
For the first time, the researchers were able to create mostly left-handed circularly polarised heat radiation in all directions using a metasurface made up of an array of F-shaped structures, resulting in non-vanishing optical helicity. The team’s design achieved 39% of the basic limit in optical helicity, and they also demonstrated that the characteristics of released thermal photons may be tuned by the metasurface’s symmetries, proving effective control over thermal radiation in its many aspects.
“This discovery has the potential to have significant ramifications for understanding the ubiquitous thermal radiation phenomena and generating new technologies,” Jacob added. The metasurface might be used as a wide-angle, narrow-band circular-polarized mid-infrared light source for optical gas sensing and infrared imaging. Furthermore, the manufactured thermal emission’s unique spectrum, spatial, and spin properties may be used as passive infrared beacons in outdoor contexts, making them helpful in remote sensing technologies.
“We are quite thrilled about the possibilities of this finding,” Ph.D. student Xueji Wang said. “It not only expands our knowledge of thermal radiation, but it also offers up new avenues for technological growth in a range of disciplines.”
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