But MIT researchers expect that their new approach to making a mirror will take much of the scientific community by surprise. This would open up a myriad of technological and research possibilities. The familiar metallic mirror is omnidirectional, which means it reflects light from every angle. It also absorbs a significant portion of the incident light. Dielectric mirrors, unlike metals, do not conduct electricity and therefore can reflect light more efficiently.
Light travels in dielectric materials at speeds that are lower than in air.
When light traveling in a particular direction through one type of dielectric material encounters another type, part of the light is reflected while the other part is transmitted at a different angle. Dielectric mirrors are made of multiple layers of transparent dielectric materials. Such materials, which can be made to be extremely low loss compared to their metallic counterparts, are used to reflect a prescribed range of frequencies coming from within a limited set of angles. Dielectric mirrors are used in devices such as lasers, which need very high reflectivity. The new kind of mirror developed at MIT can reflect light from all angles and polarizations, just like metallic mirrors, but also can be as low-loss as dielectric mirrors.