Calculated enhancement for intracavity spectroscopy with a single-mode laser

A semiclassical description of the laser is employed to calculate the change in laser intensity due to the small perturbation of an absorbing medium within the laser cavity. The laser is assumed to be operating in a single-mode near its threshold of oscillation. An expression is derived for the enhancement in detection sensitivity of laser intracavity absorption measurements over conventional absorption measurements and estimates of detection sensitivity are given