6. Role of the optical cavity

6.1 Laser oscillator

All the pieces of the puzzle seem to be in place: choice of active medium pumping mechanism and knowledge of the emission lines. However, we know that a single pass of the incident wave triggers a stimulated emission which produces a limited amplifying effect. Moreover, the assumption in the calculation requires a unidirectional effect (figure  6 ). If the active medium is placed between two plane parallel mirrors, these difficulties disappear. The amplification becomes periodic and directivity is assured because the sole preferred direction of propagation is...