Laser science the laser and maser in 1917, via a paper in which he re-derived Max Planck’s law of radiation using a formalism based on probability coefficients (Einstein coefficients) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation. The existence of stimulated emission was confirmed in 1928 by Rudolf W. Ladenburg. In 1939, Valentin A. Fabrikant made the earliest laser proposal. He specified the conditions required for light amplification using stimulated emission. In 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission; in 1950, Alfred Kastler
Sound amplification by stimulated emission of radiation are more excited electrons than electrons in the lowest energy state in the system. As electron releases energy (e.g. phonon) it interacts with another excited electron to release its energy too. Therefore, we have a stimulated emission, which means a lot of energy (e.g., acoustic radiation, phonons) is released at the same time. One can mention that the stimulated emission is a procedure where we have a spontaneous and an induced emission at the same time. The induced emission comes from the pumping procedure and then is added to the spontaneous emission. A SASER device should consist of a pumping