Forget about leprechauns, engineers are catching rainbows

February 15, 2013

BUFFALO, N.Y. - University at Buffalo engineers have created a more efficient way to catch rainbows, an advancement in photonics that could lead to technological breakthroughs in solar energy, stealth technology and other areas of research.

Qiaoqiang Gan, PhD, an assistant professor of electrical engineering at UB, and a team of graduate students described their work in a paper called "Rainbow Trapping in Hyperbolic Metamaterial Waveguide," published Feb. 13 in the online journal Scientific Reports.

They developed a "hyperbolic metamaterial waveguide," which is essentially an advanced microchip made of alternate ultra-thin films of metal and semiconductors and/or insulators. The waveguide halts and ultimately absorbs each frequency of light, at slightly different places in a vertical direction (see image at http://www.buffalo.edu/news/releases/2013/02/016.html), to catch a "rainbow" of wavelengths.

Gan is a researcher within UB's new Center of Excellence in Materials Informatics.

"Electromagnetic absorbers have been studied for many years, especially for military radar systems," Gan said. "Right now, researchers are developing compact light absorbers based on optically thick semiconductors or carbon nanotubes. However, it is still challenging to realize the perfect absorber in ultra-thin films with tunable absorption band.

"We are developing ultra-thin films that will slow the light and therefore allow much more efficient absorption, which will address the long existing challenge."

Light is made of photons that, because they move extremely fast (i.e., at the speed of light), are difficult to tame. In their initial attempts to slow light, researchers relied upon cryogenic gases. But because cryogenic gases are very cold - roughly 240 degrees below zero Fahrenheit - they are difficult to work with outside a laboratory.

Before joining UB, Gan helped pioneer a way to slow light without cryogenic gases. He and other researchers at Lehigh University made nano-scale-sized grooves in metallic surfaces at different depths, a process that altered the optical properties of the metal. While the grooves worked, they had limitations.

For example, the energy of the incident light cannot be transferred onto the metal surface efficiently, which hampered its use for practical applications, Gan said.

The hyperbolic metamaterial waveguide solves that problem because it is a large area of patterned film that can collect the incident light efficiently. It is referred to as an artificial medium with subwavelength features whose frequency surface is hyperboloid, which allows it to capture a wide range of wavelengths in different frequencies including visible, near-infrared, mid-infrared, terahertz and microwaves.

It could lead to advancements in an array of fields.

For example, in electronics there is a phenomenon known as crosstalk, in which a signal transmitted on one circuit or channel creates an undesired effect in another circuit or channel. The on-chip absorber could potentially prevent this.

The on-chip absorber may also be applied to solar panels and other energy-harvesting devices. It could be especially useful in mid-infrared spectral regions as thermal absorber for devices that recycle heat after sundown, Gan said.

Technology such as the Stealth bomber involves materials that make planes, ships and other devices invisible to radar, infrared, sonar and other detection methods. Because the on-chip absorber has the potential to absorb different wavelengths at a multitude of frequencies, it could be useful as a stealth coating material.
-end-
Additional authors of the paper include Haifeng Hu, Dengxin Ji, Xie Zeng and Kai Liu, all PhD candidates in UB's Department of Electrical Engineering. The work was sponsored by the National Science Foundation and UB's electrical engineering department.

To view this story online, with downloadable images, go to www.buffalo.edu/news.

University at Buffalo

Related Solar Energy Articles from Brightsurf:

'Transparent solar cells' can take us towards a new era of personalized energy
Solar power has shown immense potential as a futuristic, 'clean' source of energy.

CU Denver researcher analyzes the use of solar energy at US airports
By studying 488 public airports in the United States, University of Colorado Denver School of Public Affairs researcher Serena Kim, PhD, found that 20% of them have adopted solar photovoltaic (PV), commonly known as solar panels, over the last decade.

Researchers develop molecule to store solar energy
Researchers at Linköping University, Sweden, have developed a molecule that absorbs energy from sunlight and stores it in chemical bonds.

Converting solar energy to hydrogen fuel, with help from photosynthesis
Global economic growth comes with increasing demand for energy, but stepping up energy production can be challenging.

New nanodevice could use solar energy to produce hydrogen
Amsterdam, June 9, 2020 - Solar energy is considered by some to be the ultimate solution to address the current energy crisis and global warming and the environmental crises brought about by excessive consumption of fossil fuels.

Physicists develop approach to increase performance of solar energy
Experimental condensed matter physicists in the Department of Physics at the University of Oklahoma have developed an approach to circumvent a major loss process that currently limits the efficiency of commercial solar cells.

Lasers etch a 'perfect' solar energy absorber
In Light: Science and Applications, University of Rochester researchers demonstrate how laser etching of metallic surfaces creates the ''perfect solar energy absorber.'' This not only enhances energy absorption from sunlight, but also reduces heat dissipation at other wavelengths.

Mapping the energy transport mechanism of chalcogenide perovskite for solar energy use
Researchers from Lehigh University have, for the first time, revealed first-hand knowledge about the fundamental energy carrier properties of chalcogenide perovskite CaZrSe3, important for potential solar energy use.

New hybrid device can both capture and store solar energy
Researchers have reported a new device that can both efficiently capture solar energy and store it until it is needed, offering promise for applications ranging from power generation to distillation and desalination.

Materials that can revolutionize how light is harnessed for solar energy
Columbia scientists designed organic molecules capable of generating two excitons per photon of light, a process called singlet fission.

Read More: Solar Energy News and Solar Energy Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.