Answer to Question #271658 in Physics for Almas Bashir

Question

Why population inversion are necessary for lasing action.

Answer 1

Population inversion is the state in which the number of atoms in higher energy state is more than those in lower energy state.

It is required in laser so that stimulated emission is more probable than induced absorption.

Generally, more no. of atoms are in lower energy states. When a photon having energy equal to the energy difference of two states of atom is incident, the probability of ir getting absorbed is ore as lower energy lower atom are more.

However, in population inversion state, the probability of photon causing stimulated emission is more a s more atoms are in higher energy state, causing amplification of light.