An optical amplifier is a device which receives some input signal light and generates an output signal with higher optical power. Typically, inputs and outputs are laser beams (very rarely other types of light beams), either propagating as Gaussian beams in free space or in a fiber. The. 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. This means that over a distance of 100km, a signal can lose around 20dB. The input light is amplified as it passes through a gain medium. When the gain medium is externally pumped (electrically or optically), a population inversion between. Optical amplifiers are a key component in modern optical communication and networking systems.