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Unlocking Chirality: Scientists Develop Novel Metasurfaces for Advanced Optical Control
EPFL, Switzerland – In a breakthrough with far-reaching implications for fields ranging from medicine too data security, scientists have developed a revolutionary new method for precisely controlling molecular “handedness,” or chirality, using artificial optical structures called metasurfaces. This innovation, detailed in the latest issue of Nature Communications, offers a powerful new toolkit for manipulating light and has the potential to unlock advanced applications in anticounterfeiting, biosensing, and quantum technologies.
Chirality, the property of a molecule existing in two mirror-image forms, is essential to life. Most DNA and sugars are right-handed,while amino acids,the building blocks of proteins,are predominantly left-handed. This subtle difference is critical; altering a molecule’s handedness can render it biologically inactive, or even harmful.
Light itself can also exhibit chirality. When circularly polarized, light’s electric field corkscrews through space in either a left-handed or right-handed spiral. Chiral structures interact differently with these twisted light beams, allowing scientists to probe a sample’s inherent handedness by observing how it absorbs, reflects, or delays each type of polarized light. However, this interaction is typically very weak, making precise control of chirality a important challenge.
Researchers at EPFL’s Bionanophotonic Systems Laboratory, in collaboration with Australian scientists, have overcome this hurdle by creating refined metasurfaces. These are two-dimensional lattices composed of meticulously designed nanoscale elements, or ”meta-atoms.” by precisely controlling the orientation of these meta-atoms within the lattice, the team can finely tune the metasurface’s chiral properties and its interaction with polarized light.
“Our ‘chiral design toolkit’ is elegantly simple,and yet more powerful than previous approaches,which tried to control light through very complex meta-atom geometries,” explains Hatice Altug,head of the Bionanophotonics Lab. “Instead, we leverage the interplay between the shape of the meta-atom and the symmetry of the metasurface lattice.”
The team’s innovative metasurface, constructed from germanium and calcium difluoride, features a gradient of meta-atoms whose orientations vary continuously across a chip. This intricate design, combining meta-atom shape, angles, and lattice symmetry, allows for unprecedented control over the metasurface’s response to polarized light.
In a compelling proof-of-concept experiment, the scientists demonstrated the ability to encode two distinct images simultaneously onto a metasurface designed for the invisible mid-infrared spectrum. One image, a cockatoo, was encoded in the size of the meta-atoms (acting as pixels) and revealed with unpolarized light. The second image, the iconic Swiss Matterhorn, was encoded using the orientation of the meta-atoms and became visible only when the metasurface was illuminated with circularly polarized light.
“This experiment showcased our technique’s ability to produce a dual layer ‘watermark’ invisible to the human eye, paving the way for advanced anticounterfeiting, camouflage and security applications,” says Ivan Sinev, a researcher at the Bionanophotonics Systems Lab.
Beyond its potential for robust data encryption and anticounterfeiting measures, this breakthrough holds significant promise for quantum technologies, manny of which rely on the precise manipulation of polarized light for computation. Moreover,the ability to map chiral responses across large surfaces could revolutionize biosensing.”We can use chiral metastructures like ours to sense,such as,drug composition or purity from small-volume samples,” notes Felix Richter,another researcher at the Bionanophotonics Systems Lab. “Nature is chiral, and the ability to distinguish between left- and right-handed molecules is essential, as it could make the difference between a medicine and a toxin.”
This pioneering work represents a significant leap forward in our ability to control and utilize chirality, opening doors to a new era of advanced optical technologies.