Distinction between Spontaneous and Stimulated Emission of Radiation

Some of the differences between spontaneous and stimulated emission of radiation are given as follows:

1. In spontaneous emission, an atom in excited state falls to the ground state on its own without any incident photon while in stimulated emission transition takes place by stimulating photons or by an external agency.

2. In stimulated emission for each incident photon there are two outgoing photons in the same direction while in spontaneous emission the emitted photons move randomly in any direction.

3. The photons emitted in spontaneous emiss ion have a random phase and hence are incoherent while in stimulated emission the emitted photons are in phase and hence are coherent.

4. The rate of spontaneous emission is proportional to only the number of atoms in the excited state while the rate of stimulated emission is proportional to the number of atoms left in the excited state as well as on the energy density of the incident radiation.

5. In stimulated emission of radiation an amplified beam is achieved while in spontaneous emission there is no such amplification.

6. The light emitted through the spontaneous emission is not monochromatic while in stimulated transition monochromatic radiation is obtained.

7. Spontaneous emission is not controllable from outside while stimulated emission is controllable from outside.

8. In spontaneous emission, the net intensity is proportional to the number of radiating atoms while in stimulated emission it is proportional to the square of the number of radiation atoms.