IGNOU PHE 9 2018 - Derive an expression to show that the condition of population inversio

Question

Derive an expression to show that the condition of population inversion is necessary

for laser action.

27 Jan 2018

Answer :

Word Count : 452

To understand the concept of a population inversion, it is necessary to understand some thermodynamics and the way that light interacts with matter. To do so, it is useful to consider a very simple assembly of atoms forming a laser medium.

Assume there are a group of N atoms, each of which is capable of being in one of two energy states: either

The ground state, with energy E1; or

The excited state, with energy E2, with E2 > E1.

The number of these atoms which are in the ground

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