Material That Slows Light Opens New Possibilities in Solar Energy

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.

They developed a hyperbolic metamaterial waveguide, which is an advanced microchip made of alternate ultra-thin films of metal and semiconductors and insulators. The waveguide halts and ultimately absorbs each frequency of light, at slightly different places in a vertical direction, to catch series of wavelengths.

Electromagnetic absorbers have been studied for many years, especially for military radar systems. 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.

 Ultra-thin films are developed that will slow the light and therefore allow much more efficient absorption. Light is made of photons; because they move extremely fast are difficult to control. In their initial attempts to slow light, researchers relied upon cryogenic gases. But because cryogenic gases are very cold, this process is not industrially feasible.

Earlier researchers made nano-scale-sized grooves in metallic surfaces at different depths, which altered the optical properties of the metal. While the grooves worked, they had limitations; the energy of the incident light cannot be transferred onto the metal surface efficiently, which hindered its use for practical applications. 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.

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.

 

 

For further reading: http://www.nature.com/srep/2013/130213/srep01249/full/srep01249.html