Coherent addition (or coherent combining) of lasers is a method of power scaling. It allows increasing the output power and brightness of single-transversal mode laser.
Usually, the term coherent addition applies to fiber lasers. As the ability of pumping and/or cooling of a single laser is saturated, several similar lasers can be forced to oscillate in phase with a common coupler. The first nonlinear theory of the coherent addition of laser sets had been developed by Nikolay Basov with co-workers in 1965. For Nd:YAG laser set beam combination had been realized by means of SBS phase conjugating mirror. The coherent addition was demonstrated in power scaling of Raman lasers.