Theory of intracavity detection using a tunable semiconductor laser with an external resonator

A theory is developed of the behavior of a semiconductor laser with an external resonator when frequency-selective losses are introduced into the resonator. The equations of lasing kinetics are deduced allowing for spontaneous radiation and quantum noise. Expressions are obtained for the amplitude of the signal and the limit of detection of intracavity absorption for arbitrary values of an external optical feedback, intensity of spontaneous transitions, and rate of tuning of the frequency of the internal resonator.