Laser diffraction limit. All such devices are classified as "lasers" based on their method of producing light, i.e., stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies. The word "laser" started as an acronym for "light amplification by stimulated emission of radiation". In this usage, the term "light" includes electromagnetic radiation of any frequency, not only visible light, hence the terms "infrared laser", "ultraviolet laser", "X-ray laser" and "gamma-ray laser". Because the microwave predecessor of the laser, the maser, was developed first, devices of this sort operating at microwave
Sound amplification by stimulated emission of radiation operates at about 440 GHz, while the Caltech device operates in the megahertz range. According to a member of the Nottingham group, the two approaches are complementary and it should be possible to use one device or the other to create coherent phonons at any frequency in the megahertz to terahertz range. A significant result rises from the operating frequency of these devices. The differences between the two devices suggest that SASERs could be made to operate over a wide range of frequencies. Work on the SASER continues at the University of Nottingham, the "Lashkarev Institute of Semiconductor Physics" at