Classical theory of laser noise

The classical theory of laser noise treats light in a classical manner, yet agrees with quantum theory for large particle numbers. The basic concept is that laser noise is caused by atomic jumps between lower and upper levels, and that atoms subjected to classically-prescribed optical fields are independent. The treatment of amplitude noise of single-mode cavities containing resonant three-level atoms is applicable to semiconductor lasers at moderate power. At high power one must account for the dependence of the gain on optical power and for state-occupancy fluctuations. The phasor theory that attributes noise to the beat between the oscillating field and the field spontaneously emitted in the mode by excited-state atoms cannot be understood consistently in semiclassical terms.