A New Type of Medium Interface Features Negative Refraction

A new type of medium interface features negative refraction or, depending on the angle of incidence, positive (conventional) refraction. This switch-hitting optical ability (the technical name for it is "amphoteric" refraction) is a first. Furthermore, the same type of interface can be used to refract (negative or positive) a ballistic beam of electrons (electrons traveling, as waves, over a very short distance in a straight line). Refraction, a change in direction, is what happens when light waves (or other kinds of waves) move from a material with one index of refraction (say, air) into a medium (water, say) with a different index. Physicists at the National Renewable Energy Lab in Colorado have devised their material sample not from a collection of tiny rods and split rings mounted on boards, as was the case with previously reported negative-refraction materials. Instead they used a YVO4 bicrystal. Negative-refraction materials are also called "left handed materials," or LHM, because they refract light in a way which is contrary to the normal "right handed" rules of electromagnetism (see past summary in Update #628). LHM researchers hope that the peculiar properties will lead to superior lenses, and might provide a chance to observe some kind of negative analog of other prominent optical phenomena, such as the Doppler shift and Cerenkov radiation. According to Yong Zhang (303-384-6617), an additional feature of their material is that it inhibits all reflection. When considering the refraction process, reflection can be thought of as a sort of energy-loss penalty paid by waves when they are refracted, and so a reflection-less lens would be of enormous value in, for example, the transport of high-power laser beams. (Zhang et al., Physical Review Letters, 10 October 2003; see figure)