U-M Researchers Develop Small Device That Bends Light, Distinguishes Between Cancerous and Healthy Tissue

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Physicists at the University of Michigan in Ann Arbor today announced they have developed a device the size of a match head that can bend light inside a crystal to generate synchrotron radiation.

This type of radiation can be used to study the behavior of atoms and molecules, scan for items hidden in clothing and packaging crates, and generate imaging for the biomedical sciences.

“Terahertz radiation is useful for imaging in the biomedical sciences,” says Meredith Henstridge, one of the U-M researchers, lead author of the study, and a postdoctoral scientist at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany.

“For instance, it has been used to distinguish between cancerous and healthy tissue. An on-chip, single-frequency terahertz source, such as a tiny light-driven synchrotron such as our device, can allow for new advancements in all of these applications.”

When physicists bend very intense beams of charged particles in circular orbits near the speed of light, the bending throws off bits of light, or X-rays, called synchrotron radiation. The researchers used their device to bend visible light to produce light in a wavelength in the terahertz range. This range of wavelength is larger than that of visible light but smaller than waves produced by microwaves. They can penetrate clothing.

Synchrotron radiation is usually generated at large-scale facilities, typically the size of several football stadiums. U-M researchers Henstridge, Roberto Merlin, and their team printed a pattern of microscopic gold antennae on the polished face of a lithium tantalite crystal, called a metasurface.

The team, which also included researchers from Purdue University, used a laser to pulse light through the pattern of antennae, which bent the light and produced synchrotron radiation.

“Instead of using lenses and spatial light modulators to perform this kind of experiment, we figured out by simply patterning a surface with a metasurface, you can achieve a similar end,” says Merlin, professor of physics, and electrical engineering and computer science. “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.”

Anthony Grbic, professor of electrical engineering and computer science at U-M, led the team that designed the metasurface, which is composed of about 10 million tiny boomerang-shaped antennae. Each antenna is smaller than the wavelength of the impinging light, says Henstridge. The researchers use a laser that produces ultrashort bursts or pulses of light that last for one trillionth of a second. The array of antennae causes the light pulse to accelerate along a curved trajectory inside the crystal.

The light creates a collection of electric dipoles, or a group of positive and negative charge pairs. This collection accelerates along the curved trajectory of the light pulse, resulting in the emission of synchrotron radiation.

The device produces synchrotron radiation that contains many terahertz frequencies because the light pulses travel just a fraction of a circle. The researchers hope to refine their device so the light pulse revolves continuously along a circular path, producing synchrotron radiation at a single terahertz frequency.

The study was published in the journal Science.

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