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About Population Inversion in Laser - Definition, Diagram

Do you want to know about population inversion ? Here is the complete information on this topic of laser population inversion.In this we discuss in details on this topic.Laser light is totally different from conventional light. 
In conventional light sources,there is no coordination among different atoms emitting radiation.
There will be a population inversion occurs where more atoms are present in high energy states than in low ones.

Population Inversion


Population inversion is explained by levels E1, E2 and E3 of a system.Explain that E1, E2 and E3 are the excited states of ground state, metastable state, and system energies, respectively, such as E1 <E2 <E3. In a system, the population of atoms (N) at an energy level E, expressed at absolute temperature T .In terms of population (N1) in the ground state using Boltzmann's distribution law.

N = N1 exp (−E / KBT ) where KB = Boltzmann’s constant

population inversion diagram
population inversion diagram 

Definition of Population inversion 

Generally, the number of atoms (N1) present in the ground state (E1) in the system is larger than the number of atoms (N2) present in the high energy state. The process of making N2> N1 is called the population inverse.

Conditions for population inversion 

These are the Conditions for population inversion :

(a) The system must have a pair of at least one energy level (E2> E1), separated by an energy equal to the energy of a photon (hν).

(b) There should be a continuous supply of energy to the system such that atoms must be continuously raised in excited state.

Population inversion between E1 and E2 energy levels

How Population inversion can be achieved 

Population inversion can be achieved by following numbers of ways. Some of them are: 
(i) optical pumping 
(ii) electrical discharge 
(iii) inelastic collision of atoms
(iv) chemical reaction and 
(v) direct conversion.
In lasers, if the active medium is a transparent dielectric, the optical pumping method is used. If the active medium is conductive, the electric field is used to produce a population inverse.


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