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A material capable of halting and absorbing light is making "catching" rainbows possible. The innovative material is the work of Qiaoqiang Gan, a PhD researcher and an assistant professor of electrical engineering along with graduate students from the University of Buffalo (UB). They published a paper with their findings in February 2013 titled “Rainbow Trapping in Hyperbolic Metamaterial Waveguide”.
Research Behind New Breakthrough
Based on previous research carried out by Dr. Gan, the basis of the concept of hyperbolic metamaterials was from the electromagnetic absorbers currently used in military radar systems and compact light absorbers based on optically thick semiconductors or carbon nanotubes. Dr. Gan used these technologies as inspiration to try to develop absorbers in ultra-thin films with tuneable absorption bands.
As light moves at an incredibly fast speed, they are very difficult to tame and so originally cryogenic gases were used to slow the light down. Due to the extremely cold temperature of cryogenic gases, working outside laboratories with it was difficult. Dr. Gan had previously worked on research where he found a way to slow light without using cryogenic gases. Along with a team from Lehigh University, Dr. Gan created nanoscale-sized grooves in metallic surfaces at different depths which altered the optical properties of the metal.
Despite the success of the grooves, they did have limitations. One such drawback was that the energy of the incident light could not be transferred efficiently onto the metallic surface which in turn created issues with practicality.This issue was solved by the use of a hyperbolic metamaterial waveguide.
How does a Hyperbolic Metamaterial Waveguide Work
The hyperbolic metamaterial waveguide is essentially an advanced microchip composed of alternate ultra-thin films of metal and insulators and/or semiconductors. The waveguide is a large area of patterned film that stops light and absorbs different frequencies at slightly different places in a vertical direction, thereby catching a “rainbow” of wavelengths.
Hyperbolic metamaterials explained in 5 minutes
Video sourced from: Youtube - Dr. Quark
The waveguide can also be referred to as an artificial medium with subwavelength characteristics. Its surface frequency is hyperboloid, thus enabling the capture of a wide range of wavelengths in different frequencies including visible, mid-infrared, near-infrared, microwaves, and terahertz.
Benefits and Future Applications
The achievement of the UB research team is a huge step in the field of photonics, which could lead to significant technological breakthroughs in stealth technology, solar energy, and a variety of other fields. Light can now be manipulated for optical modulation, communication, switching, and light-matter interactions.
Dr. Gan states that the hyperbolic metamaterial waveguide can be applied to solar panels and other energy-harvesting devices. It could also be very useful in mid-infrared spectral regions as a thermal absorber for devices that recycle heat after sunset.
As the metamaterial absorber has the capacity to capture different wavelengths at a large amount of frequencies, it could be applied as a stealth coating material for aircraft or ships, thereby rendering them invisible to radar, infrared, sonar and other detection methods.
In the field of electronics, a phenomenon known as crosstalk occurs where a signal transmitted on one circuit causes an unwanted effect in another circuit. The waveguide absorber also has the potential to prevent this.
Photons are difficult to control, and they move at the speed of light. The ability to stop and control them for human use is indeed a major breakthrough in technology. The achievement of Dr. Gan and his team is very impressive and the numerous potential applications for the technology is remarkable.