Spontaneous and Stimulated Emissions

SPONTANEOUS AND STIMULATED EMISSIONS

Process - 2 

Spontaneous emission

The atom in the excited state E2 (higher energy state) returns to ground state E1 (lower energy state) by emitting a photon of energy hv (ΔE = E2- E1) without the influence of any external agency (Fig. 5.2).

Such emission of light radiation which is not triggered by any external influence is called spontaneous emission.

It is a random and also uncontrollable process.

Process - 3 

Stimulated emission

Einstein suggested that there must be another mechanism by which an atom in excited state can return to ground state.

He found that there is an interaction between the atom in excited state and a photon. During this interaction, the photon triggers the excited atom to make transition to ground state E1 (Fig. 5.3).

This transition produces a second photon which is similar to triggering photon with respect to frequency, phase and propagation direction.

Such kind of forced emission of photons by the incident photons is called stimulated emission. It is also known as induced emission. It plays a key factor