激光是二十世纪继原子能和半导体之后,在六十年代初迅速发展起来的又一项重大新技术。激光也是一种光。它与普通光的不同处在于:普通光是原子系统自发辐射占优势,而激光是原子系统受激辐射占优势。激光具有三个“集中”的特性。即(一)激光能量在空间高度集中,表现为在传播方向上高度集中和发光截面上的集中,即亮度很高。(二)激光能量在时间上高度集中,能在极短的时 Laser was another major new technology developed rapidly in the early 1960s after the atomic and semiconductor in the twentieth century. Laser is also a light. It differs from ordinary light in that ordinary light is dominated by spontaneous emission from atomic systems, and laser is dominated by stimulated radiation from atomic systems. Laser has three “focused” features. That is, (a) the laser energy is highly concentrated in space, which manifests itself in high concentration in the direction of propagation and concentration in the light-emitting cross-section, ie, high brightness. (B) laser energy is highly concentrated in time, in a very short time