Four characteristics of laser

 Along a straight line rather than divergence

-High brightness

 In the high concentration of space and time, it can get very high energy from the unit area and time.

-High security

 The spectral width is very narrow and the color is very pure. It is divided into infrared light and ultraviolet which is called common light.

-High coherence

 The same frequency, and the vibration direction of the same two wave has a phase constant encounter department. Laser can  maintain a constant phase difference time.