The ability of any material to amplify light has tremendous possibilities for improvement of technologies that use light to make energy for example. When glass lens or parabolic reflectors are used to focus light before it impacts the surface of a solar cell, the power output of the cell is amplified.
What if the material itself could somehow amplify the light with out the use of huge and expensive peripheral reflection devices? It seems that one research team at UW-Madison has done just that.
In a paper published July 10, 2015 in the journal Physical Review Letters, Zongfu Yu, an assistant professor of electrical and computer engineering at UW-Madison, PhD student Ming Zhou, and their collaborators describe nanoscale device that that drastically outpaces previous technology in its ability to scatter light. They showed how a single nanoresonator can manipulate light to cast a very large “reflection.” The nanoresonator’s capacity to absorb and emit light energy is such that it can make itself—and, in applications, other very small things—appear 10,000 times as large as its physical size.
“Making an object look much 10,000 times larger than its physical size has lots of implications in technologies related to light,” Yu says.
The researchers realized the advance through materials innovation and a keen understanding of the physics of light. Much like sound, light can resonate, amplifying itself as the surrounding environment manipulates the physical properties of its wave energy. The researchers took advantage of this by creating an artificial material in which the wavelength of light is much larger than in a vacuum, which allows light waves to resonate more powerfully.
The device condenses light to a size smaller than its wavelength—meaning it can gather a lot of light energy—and then scatters the light over a very large area—meaning its output can be harnessed for imaging applications that make microscopic particles appear huge.
“The device makes an object super-visible by enlarging its optical appearance with this super-strong scattering effect,” Zhou says.
Much as a very thin string on a guitar can absorb a large amount of acoustic energy from its surroundings and begin to vibrate in sympathy, this one very small optical device can receive light energy from all around and yield a surprisingly strong output. In imaging, this presents clear advantages over conventional lenses, whose light-gathering capacity is limited by direction and size.
“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,” Yu says.
Given the nanoresonator’s capacity to absorb large amounts of light energy, the technology also has potential in applications that harvest the sun’s energy with high efficiency. In addition, Yu envisions simply letting the resonator emit that energy in the form of infrared light toward the sky, which is very cold. Because the nanoresonator has a large optical cross-section—that is, an ability to emit light that dramatically exceeds its physical size—it can shed a lot of heat energy, making for a passive cooling system.
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.
Zhou and Yu co-authored the Physical Review Letters paper with Lei Shi and Jian Zi of Fudan University in China. Yu’s research is supported by the Office of Naval Research and the Wisconsin Alumni Research Foundation (WARF).
Article and picture credit go to UW-Madison, PhD student Ming Zhou
About the picture
A diagram shows an optical nanoresonator embedded within a slab of low-index material to test its performance.
Gordon's expertise in the area of industrial energy efficiency and alternative energy. He is an experienced electrical engineer with a Masters degree in Alternative Energy technology. He is the co-founder of several renewable energy media sites including Solar Thermal Magazine.