A nonlinear material capable of backward phase matching has been developed by researchers at the School of Electrical and Computer Engineering at Georgia Tech. Such a material does not exist in nature, but the idea was first theorized a decade ago.
A nonlinear mirror, as the material is also known, is able to direct light in ways that normal mirrors cannot. In standard mirrors, the angle of incidence is equal to the angle of reflection. For example, if a beam of light strikes a mirror at 45 degrees, it will bounce off at 45 degrees from the surface. Because of this, if you can see someone in a mirror, they can also see you. But if a beam of light strikes a nonlinear mirror at a 45-degree angle, it might bounce of at a 60-degree angle, for example. This property opens up possibilities not avalaible with standard materials.
Engineered metamaterials have already been used to develop faster computer chips, more efficient solar cells, sensing devices and invisibility cloaks, albeit with limited success.
For years, researchers have attempted to develop a negative-index material. Light, like a guitar string being plucked, has both fundamental and harmonic frequencies. When a note is played on a guitar, the string produces not just that single note, but other related notes as well. This property is one important aspect of why the same note sounds different on a saxophone compared than it does on a piano. In order to create this first negative-index material, researchers had to alter the refractive index at the fundamental as well as harmonic frequencies.
The development of the nonlinear mirror is not likely to be used to develop new technologies in the short term. However, researchers hope the new material could lead to a wave of new discoveries and inventions in the near future.
"[S]tudies of nonlinear metamaterials may have a revolutionary impact on the field of nonlinear optics. The unconventional electromagnetic parameters made possible by metamaterials will provoke us to rethink and re-evaluate many of the established rules of nonlinear optics," said Wenshan Cai from Georgia Tech's School of Electrical and Computer Engineering.
The known laws of physics governing non-linear optics could also be greatly expanded by the development of the new material.
Metamaterials, constructed of small repeated units of material, have a unique effect on light. At frequencies between that of red and infrared, these units can act as "meta-atoms" in order to alter the path of light in ways not possible using natural materials.
Light travels through materials at specific speeds, depending on the substance. As it passes from one medium to another, as when it goes from air into glass, it bends. This new metamaterial is composed of two flat sheets of silver, with a thin dielectric sheet between them.
Development of the new metamaterial was detailed in the journal Nature Materials.