When light of suitable frequency incident on the substance, the atom of the substance go to the excited states by absorbing this light. The atom in the excited state come to the ground state or lower energy state by the emission of light or electromagnetic radiation.
Einstein predicted that the emission of light or electromagnetic radiation by an atom may be Spontaneous Emission and Stimulated Emission.
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Spontaneous Emission and Stimulated Emission
There are two types of emission
- Spontaneous Emission
- Stimulated Emission
Spontaneous Emission
The atom in the excited state jumps back to the ground state by emitting a photon of energy ( hv = E2 – E1 ) without the aid of external agency after 10-8 s. Such emission of radiation is known as spontaneous emission. This process is random and the emitted radiation are incoherent.
Stimulated Emission
In 1917, Albert Einstein predicted another type of emission known as Stimulated emission of radiation in addition to the spontaneous emission of radiation.
An atom in the exited state can also be forced to jump to the ground state by emitting a photon of energy hv. When a photon of energy hv (called stimulated photon) is incident on the atom in the excited state, then this atom jumps to the ground state by emitting another photon of energy hv. Such emission is known as stimulated emission.
In this process, two photons each having energy hv come out. These photons are exactly in phase. Thus, we get coherent photons or radiation. These photon can stimulate other atoms in the excited state to emit photons in a chain of similar process. This multiplication of photons ( or amplification) give rise to intense, monochromatic, coherent and unidirectional beam of LASER.
Frequently Asked Questions on Spontaneous Emission and Stimulated Emission
What is meant by spontaneous emission?
The atom in the excited state jumps back to the ground state by emitting a photon of energy ( hv = E2 – E1 ) without the aid of external agency after 10-8 s. Such emission of radiation is known as spontaneous emission.
What is meant by stimulated emission?
When a photon of energy hv (called stimulated photon) is incident on the atom in the excited state, then this atom jumps to the ground state by emitting another photon of energy hv. Such emission is known as stimulated emission.