Explain

The principle behind the laser is like this. Suppose we can produce a large number of atoms all in excited states. If one of the atoms emitted spontaneously, then the emitted photon would stimulate other atoms to emit. These emitted photons would, in turn, stimulate further emission. The result would be an intense burst of coherent radiation.

These issues have been discussed below: A representative laser system is shown in Figure (2). It consists of three basic parts.

 

	An active medium with a suitable set of energy levels to support laser action.		A source of pumping energy in order to establish a population inversion.
	An optical cavity or resonator to introduce optical feedback and so maintain the gain of the system overcoming all losses.