Sound amplification by stimulated emission of radiation to the statement that the levels on which the laser should operate, must be in the k-space relatively to each other. K-space refers to a space where things are in terms of momentum and frequency instead of position and time. The conversion between real space and k-space is a mathematical transformation called the Fourier transform and thus k-space can be also called Fourier space. We note that, the difference in energy of the photon lasing levels has to be at least smaller than the Debye energy in the semiconductor. Here we can think of the Debye energy as the maximum
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