A "PERFECT MIRROR," one that efficiently reflects a specified wavelength range of light coming in from all directions, has been built by MIT researchers (Yoel Fink, 617-253-8454), opening possibilities for energy-saving windows and better versions of optical fibers for telecommunications. Traditional metallic mirrors can reflect a wide range of colors from all directions, but they typically absorb a few percent of the light that strikes them. More recent "dielectric mirrors" (which consist of alternating layers of insulating materials) are highly reflective, but they work only for a narrow wavelength range of light hitting them straight on. Combining the best properties of both mirror types, the MIT group designed a dielectric mirror consisting of 9 alternating, micron-thick layers of the element tellurium and the polymer polystyrene. The highly contrasting indices of refraction in these layers enabled light (10-15 micron wavelength, in the infrared) coming in from all directions to be reflected at the interfaces. In addition to practical applications, the researchers speculate that this design might allow physicists to confine light for longer amounts of time than previously possible. (Fink et al., Science, 27 November 1998.)