Putting Photons to Work

15 May 2009 (All day)

Matt Eichenfield and Jasper Chan, Nature

Nano vibrator. A tiny device called a zipper cavity can convert laser light into mechanical energy.

Researchers have built a nanoscale device that vibrates when struck by incoming laser light. The contraption, which is sensitive to the energy of a single photon, could speed the development of new optical communications systems. It could also help scientists probe some of the fundamental properties of matter with greater precision.

Light beams might not seem capable of performing mechanical work (photons, the carriers of light waves, have no mass), but at the atomic level they can accomplish a surprising amount. For instance, scientists have used laser light to trap, hold, and manipulate individual atoms. The question has been whether the same principle works at the nano scale, at which components are much larger than atoms but still only billionths of a meter in size.

That's what a team from the California Institute of Technology (Caltech) in Pasadena set out to answer. First, the researchers fabricated a pair of planks only a few hundred nanometers wide out of silicon microchip material. Then they chemically etched a series of holes in each of them. The team calls the device a "zipper cavity," because of its resemblance to a zipper (see image). As the researchers report this week in Nature, the holes channel and capture a laser beam's energy and the device vibrates. The frequency of the vibrations depends on the intensity of the laser light bombarding it, says physicist and co-author Oskar Painter of Caltech.

The device behaves like an audio speaker, whose membrane vibrates depending on the intensity of an incoming electronic signal delivered by an amplifier. Conversely, like a microphone, the zipper cavity can modify the light's intensity via its vibrations. Together, the effects enable the zipper cavity to act as a tiny radio transmitter or receiver controlled entirely by light, says Painter, but with much greater range than a similarly sized electronic device.

Physicist Tobias Kippenberg of the Max Planck Institute for Quantum Optics in Garching, Germany, says that scientists could use such nanoscale devices to explore the behavior of matter at the quantum scale, at which electronic devices are unusable. Painter explains that because the device's vibrations occur on the order of 10 million to 150 million cycles per second, it could greatly improve the resolving power of atomic-force microscopes. Those devices, which are used to examine molecules and atoms, operate at only thousands of cycles per second. "The prospects are exciting for both fundamental research and new applications," Kippenberg says.

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