Sound amplification by stimulated emission of radiation mechanism and an active medium. The pumping procedure can be induced for example by an alternating electric field or with some mechanical vibrations of resonators, followed by acoustic amplification in the active medium. The fact that a SASER operates on principles remarkably similar to a laser, can lead to an easier way of understanding the relevant operation circumstances. Instead of a feedback-built potent wave of electromagnetic radiation, a SASER delivers a potent sound wave. Some methods for sound amplification of GHz-THz have been proposed so far. Some have been explored only theoretically and others have been explored in non-coherent experiments.
Negative refraction propagation direction of the light, thus the sign of "n" must be chosen to match the physical situation. The principal symptom of negative refraction is just that – light rays are refracted on the "same" side of the normal on entering the material, as indicated in the diagram, and by a suitably general form of Snell's law. Negative refraction Negative refraction is the name for an electromagnetic phenomenon where light rays are refracted at an interface in the reverse sense to that normally expected. Such an effect can be obtained using a metamaterial which has been designed to achieve a