Amplifying light a few hundred times with magnifying lenses is easy. Amplifying light by altering the resonant properties of light itself is a much more difficult proposition. However, if recent research by engineers at the University of Wisconsin-Madison (UWM) engineers is anything to go by, the effort is well worth it: They claim to have constructed a nanoscale device that can emit light as powerfully as an object more than 10,000 times its size.
According to the researchers, the light-amplifying properties of the device – known as a nanoresonator – are analogous to that of a guitar string that vibrates in sympathy to local acoustic energy. As such, this tiny optical device receives light energy from its surroundings to produce a light output much larger than expected. This, according to the team, offers many advantages in imaging techniques over normal lenses, as the device's light-harvesting ability is not limited by its physical properties to direction and size.
"Making an object look much 10,000 times larger than its physical size has lots of implications in technologies related to light," says assistant professor Zongfu Yu. "We are developing photodetectors based on this technology, and, for example, it could be helpful for photographers wanting to shoot better quality pictures in weak light conditions."
Just as sound can be made to resonate and amplify when a standing wave is generated in a low-loss reflection chamber, so too can light be amplified by an environment that manipulates the physical properties of light-wave energy. The UWM researchers exploited this fact in their research to engineer an artificial material in which the wavelength of light is much longer than in a vacuum, thereby allowing the light to resonate much more strongly.
The material also condenses light to a size smaller than its wavelength, which means that a large amount of light energy is captured before being reflected onto a much larger surface where it is widely scattered, providing a much-magnified version of the original light energy. In this way, even microscopically-small objects can be made to appear enormous in the amplified light image.
"The device makes an object super-visible by enlarging its optical appearance with this super-strong scattering effect," says PhD student of electrical and computer engineering at UWM, Ming Zhou.
With the nanoresonator’s ability to absorb copious amounts of energy from light, the team also believes that their device presents possibilities in high-efficiency solar cells. Yu believes that the ability to re-emit unwanted energy in the infrared during solar capture would allow the device to be self-cooling, further increasing its efficiency.
"This research opens up a new way to manipulate the flow of light, and could enable new technologies in light sensing and solar energy conversion," says Yu.
The results of the research were recently published in the journal Physical Review Letters.
Source: University of Wisconsin-Madison
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