In addition to absorption and spontaneous emission, Einstein deduced that a third kind of interaction must exist, one in which a photon could induce an excited atom to emit another photon.

• 除了吸收与自发放射之外，爱因斯坦推论出必须存在第三种交互作用，也就是光子会诱使受激发的原子放射出另一个光子。