Sound amplification by stimulated emission of radiation pumping energy into the system we can have a stimulated emission of radiation—which means that the pump forces the system to release a big amount of energy at a specific time. A fundamental characteristic of lasing, like the population inversion, is not actually possible in a two-level system and therefore a two level-laser is not possible. In a two-level atom the pump is, in a way, the laser itself. The amplification of coherent terahertz sound in a Wannier-Stark ladder superlattice has been achieved in 2009 according to a paper publication from the School of Physics and Astronomy in the University
Maser slightly since its introduction. Initially the acronym was universally given as "microwave amplification by stimulated emission of radiation", which described devices which emitted in the microwave region of the electromagnetic spectrum. The principle and concept of stimulated emission has since been extended to more devices and frequencies. Thus, the original acronym is sometimes modified, as suggested by Charles H. Townes, to ""molecular" amplification by stimulated emission of radiation." Some have asserted that Townes's efforts to extend the acronym in this way were primarily motivated by the desire to increase the importance of his invention, and his reputation in the scientific