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 Maser A maser (, an acronym for "microwave amplification by stimulated emission of radiation") is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, James P. Gordon, and H. J. Zeiger at Columbia University in 1953. Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are used as the timekeeping device in atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes and deep space spacecraft communication ground stations. Modern masers can be designed