一个原子吸收能量之后,从低能态到高能态的过程称为激发过程。处于激发状态的原子是不稳定的,总是自发地回到低能态, 同时有光子发出,这一过程叫“自发辐射”。如果原子吸收外界光能则跃迁到高能级,而受外界光感应产生辐射则又回到低能态,这一过程叫“受激发射”。但是,只有采用一种办法使物质中大量粒子同时处于激发态,并通过外界光感应,使所有处于激发态的粒子几乎同步完成受激辐射回到低能态,这时物质才能发出一束强大的光束,称为“激光”。打个比方,激光的产生过程好比用水泵将水抽到水塔顶部,然后突然打开闸门,这时水就会以强大的力量喷射而出。当然,激光的产生过程要远比上面的例子复杂得多。在固体激光器中,能产生激光的晶体或 After an atom absorbs energy, the process from the low energy state to the high energy state is called the excitation process. The excited atoms are unstable, always spontaneously return to the low energy state, while photons are emitted, a process called “spontaneous emission.” If the atomic absorption of external light energy is to transition to a high energy level, and the external light-induced radiation is returned to the low energy state, the process is called “stimulated emission.” However, only by using a method to make a large number of particles in the excited state at the same time, and by external light sensing, so that all particles in the excited state almost complete synchronization of the stimulated emission back to the low energy state, then the material can issue a powerful Beam, called “laser.” For example, the process of laser generation is like pumping the water to the top of the water tower with a water pump, then suddenly opening the water gate, when the water is jetted out with powerful force. Of course, the laser generation process is far more complicated than the above example. In solid-state lasers, can produce laser crystal or