5. Einstein coefficients for absorption, spontaneous emission and stimulated (or induced) emission
The reciprocal action of an electromagnetic wave and an atomic system characterized by its discrete energy levels can be treated by the processes of absorption, spontaneous emission and induced emission. Einstein defined these different mechanisms by coefficients reflecting the probabilities of each.
5.1 Absorption mechanism
Consider a cavity containing n0 atoms of which n1 are in the fundamental level, illuminated by a parallel beam of light of frequency ν, such that E2 – E1 = hν and energy spectral density ρ(ν), ρ(ν) represents the energy contained in the exciting beam per unit frequency interval and per unit volume. This density is related to the spectral energy intensity by the simple relation :
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Einstein coefficients for absorption, spontaneous emission and stimulated (or induced) emission
Resonant cavity and laser beam intensity
Bibliography
- (1) - Les Lasers et Leurs Applications Scientifiques et Médicales - Édition C. Fabre et J. P. Pocholle, Les Éditions de Physique (Paris) (1996). 1.1 C. FABRE, Les Lasers – Principes Fondamentaux, pp. 1-40. 1.2 G. BOULON, Matériaux pour Lasers à Solide, pp. 259-286. 1.3. H. MONERIE, Fibres optiques dopées et applications, - pp. 357-382. ...
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