As we have discussed in the previously, that principle of laser is stimulated emission and for it to take place, population inversion has to be achieved and maintained. For this, there must be a source of external energy, which can continuously supply energy to energy to laser medium, so that population inversion can be achieved. Such a source of external energy is called pump or pumping source and the process of supplying external energy to laser medium so as to achieve the population inversion is called pumping.

Next time we will discuss the various types of pumping source.