雷射(laser)

能产生极强干涉光（光波间有恒定相位差的光）的器件。laser一词乃英文中「将受激发而辐射的光放大」（light amplification by stimulated emission of radiation）几个英文字的第一个字母拼成的，描述了它的光束是如何产生的。第一支雷射管是梅曼（T. Maiman, 1927～）在汤斯先前的工作基础上於1960年制作出来的，用的是一段红宝石棒。从一个闪光灯发出波长合适的光，把红宝石的原子激发到更高的能级上去。受激的原子很快衰退到较低的能级（通过声子反应），然後逐渐回到基态，同时发出一定波长的光。光趋向於在红宝石棒两个抛光好的端面上来回反射，刺激进一步的发射。在显微手术、光碟（CD）播放机、通信和全息术中雷射都有很有价值的应用；雷射还可以用来在硬质材料上打孔，在隧道掘进时对准，用於远距离的测量以及描绘精致的细节等。

English version：

laser

Device that produces an intense beam of coherent light (light composed of waves having a constant difference in phase). Its name, an acronym derived from “light amplification by stimulated emission of radiation,” describes how its beam is produced. The first laser, constructed in 1960 by Theodore Maiman (born 1927) based on earlier work by Charles H. Townes, used a rod of ruby. Light of a suitable wavelength from a flashlight excited (see excitation) the ruby atoms to higher energy levels. The excited atoms decayed swiftly to slightly lower energies (through phonon reactions) and then fell more slowly to the ground state, emitting light at a specific wavelength. The light tended to bounce back and forth between the polished ends of the rod, stimulating further emission. The laser has found valuable applications in microsurgery, compact-disc players, communications, and holography, as well as for drilling holes in hard materials, alignment in tunnel drilling, long-distance measurement, and mapping fine details.