LASER stands for Light Amplification by Stimulated Emission of Radiation:
It's a fairly long string of words. Well, don't let it stop you from reading further. What we wish to bring out here is that lasers produce a very special kind of light. The light that lasers produce has several useful properties that make it different from ordinary light. It is becarise of these properties that laser light can be put to work in a number of ways. You may wonder what the difference between ordinary light and light from a laser is. Light from the Sun or from a lamp in your home is a mixture of many wavelengths. Each wavelength produces a different colour. These colours mix and form ordinary light. We have all seen colours in the sunlight separating out to form a rainbow in the sky after a rainy day. Moreover. light waves from an ordinary source of light are all jumbled up and uncoordinated in their movement.
Laser light is made up of waves of the same wavelength. What is more, all the nvavek in a laser beam are organised to proceed exactiy in step (in phase) with each other. This property of lasers is called coherence. It reminds you of contingents of smartly dressed mean moving in unison in the Republic Day parade. Or of the uniform movement of oars in boat races of Kerala held on Onam. Does it not? As a result of coherence, light waves in a laser beam can travel laige distames without spreading apart. Because a laser beam does not spread out. there is a large concentruriort of energy per unit area on the object on which the laser beam falls. "