Optical amplifiers are a key component in modern optical communication and networking systems. They have an essential role in long-distance fiber-optic communication. Optical amplifiers are used to create laser guide stars which provide feedback to the adaptive optics control systems which dynamically adjust the shape of the mirrors in the largest astronomical telescopes. An illustration of the effective gainis given below. This principle dictates that a photon can interact with an atom already in an excited energy state, forcing the excited atom to immediately release its stored energy as a second photon.
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