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Let us learn about population inversion in laser.

Population Inversion :

• Population inversion is a condition of a system in which number of atoms in the higher energy level are greater than in the number of atoms in the lower energy level.

• The E1, E2 and E3 are to be considered as the energy level of the system where, E3>E2>E1.

• In this system E1 is the ground state or normal state and E2 is the metastable state.

• The atoms get excited from state E1 to E2 by means of external source and stay there for a short period of time.

• Then the atoms undergoes continuous movement from E2 to E1.

• Population inversion is an important condition for lasing action, that allows the amplification of light.