In photonics-talk, a pump is a device that excites atoms in the gain medium of a laser or amplifier. In the case of semiconductor lasers or certain gaz lasers, the pump is directly the electrical current; in most solid-state lasers, some gaz lasers and EDFAs, the pump is light, either incoherent (from a flash lamp) or coherent (from another laser). In chemical lasers, the pump is a chemical reaction, more often exothermic, that produces vibrationally excited molecules.