Module 8 : Laser- II
Lecture   : Rate equations for Lasers
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2.10.1 Rate Equations for a Four Level System :
 

We denote the ground state as level 1 and the pumping level as level 4. Lasing transition occurs between levels 2 and 3 ( $ 2\rightarrow 3$). Let $ W_p = W_{1\rightarrow 4}= W_{4\rightarrow 1}$be pumping induced transition rate between the ground level and the uppermost level. The lifetime of the lasing transition $ \tau_{3,2}$is much greater than all other lifetimes in the problem.

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