Synchrotron Radiation in a Crystal

A new device bends visible light inside a crystal to produce synchrotron radiation via an accelerating light pulse on a scale a thousand times smaller than massive facilities around the world. (Source: Univ. of Michigan, M. Henstridge)

The DESY acce­lerator faci­lity in Hamburg, Germany, goes on for miles to host a particle making kilo­meter-long laps at almost the speed of light. Now researchers have shrunk such a facility to the size of a computer chip. A University of Michigan team in colla­boration with Purdue Univer­sity created a new device that still accom­modates speed along circular paths, but for producing lower light frequencies in the terahertz range of appli­cations such as identi­fying counter­feit dollar bills or distin­guishing between cancerous and healthy tissue.

“In order to get light to curve, you have to sculpt every piece of the light beam to a parti­cular inten­sity and phase, and now we can do this in an extremely surgical way,” said Roberto Merlin, the Univer­sity of Michigan’s Peter A. Franken Colle­giate Professor of Physics. Ultimately, this device could be con­veniently adapted for a computer chip. “The more terahertz sources we have, the better. This new source is also excep­tionally more efficient, let alone that it’s a massive system created at the milli­meter scale,” said Vlad Shalaev, Purdue’s Bob and Anne Burnett Distin­guished Professor of Electrical and Computer Engi­neering.

The device generates synchrotron-radiation, which is electro­magnetic energy given off by charged particles, such as electrons and ions, that are moving close to the speed of light when magnetic fields bend their paths. Several facilities around the world, like DESY, generate synchro­tron radiation to study a broad range of problems from biology to materials science. But past efforts to bend light to follow a circular path have come in the form of lenses or spatial light modu­lators too bulky for on-chip tech­nology.

A team led by Merlin and Meredith Hen­stridge, now a post­doctoral researcher at the Max Planck Institute for the Structure and Dynamics of Matter, substituted these bulkier forms with about 10 million tiny antennae printed on a lithium tantalite crystal, a meta­surface. The researchers used a laser to produce a pulse of visible light that lasts for one trillionth of a second. The array of antennae causes the light pulse to acce­lerate along a curved trajectory inside the crystal.

Instead of a charged particle spiraling for kilo­meters on end, the light pulse displaced electrons from their equilibrium positions to create dipole moments. These dipole moments acce­lerated along the curved tra­jectory of the light pulse, resulting in the emission of syn­chrotron radiation much more effi­ciently at the tera­hertz range. “This isn’t being built for a computer chip yet, but this work demon­strates that syn­chrotron radiation could even­tually help develop on-chip tera­hertz sources,” Shalaev said. (Source: Purdue U.)

Reference: M. Henstridge et al.: Synchrotron radiation from an accelerating light pulse, Science 362, 439 (2018); DOI: 10.1126/science.aat5915

Link: Center for Photonics and Multiscale Nanomaterials, University of Michigan, Ann Arbor, USA • Birck Nanotechnology Center, Purdue University, West Lafayette, USA

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