4. Optical amplification

With pumping and population inversion mastered and with stimulated emission once and for all accepted in order to abide by the fundamental laws of physics, the analysis of a population of excited atoms leads to an interesting result, shown in figure  5 : if n incident photons (here n  = 5) illuminate a population of atoms in an inversion state, some are going to trigger stimulated emissions by interaction with the excited atoms (3 in the figure), some others will not undergo any interaction (1 in the configuration here). On average the number of photons present can increase because the number of excited atoms...