Abstract

It has been widely accepted that the rate of spontaneous emission from an atom into any one cavity mode is on average equal to the rate of stimulated emission induced by one photon in the same mode. This can be derived from an analysis of the interaction between a collection of atoms and the quantized electromagnetic field. From this fundamental result, one can derive the Schawlow-Townes laser linewidth expression. A few years ago, however, a reformulation of the laser equations using the trae cavity eigenmodes predicted that the conventional description of quantum spontaneous emission for each cavity eigenmode should be enhanced by an excess noise factor K_p due to eigenmode nonorthogonality [1, 2]. An important consequence of this is the appearance of an excess noise factor K_p multiplying the Schawlow-Townes formula for the quantum-limited laser linewidth. The value of K_p will be only slightly larger than unity for stable-cavity lasers, but can be as large as hundreds or thousands for unstable-cavity lasers.

© 1996 Optical Society of America