Engineering Physics

10.3 Spontaneous and stimulated emission

In lasers, the interaction between matter and light is of three different types. They are: absorption, spontaneous emission and stimulated emission. In these processes, two energy levels of atoms are involved. As shown in Fig. 10.1, Let E₁ and E₂ be ground and excited states of an atom. The dot in Fig. 10.1, represents an atom. Transition between these states involves absorption or emission of a photon of energy E₂ − E₁ = hν₁₂, where ‘h’ is Planck’s constant. Now, we study these processes in detail.

 

Figure 10.1 (a) Absorption; (b) Spontaneous emission; (c) Stimulated emission

(a) Absorption: As shown ...