Abstract

One of the most fundamental properties of single-mode laser light is its narrow linewidth. The ultimate limit to this linewidth is due to quantum fluctuations. Specifically, spontaneous emission events give rise to phase diffusion of the laser light and thus to spectral broadening. This is described by the famous Schawiow-Towaes formula for the laser linewidth, $\Delta v={\Gamma }_c/2n=\pi hv{\Gamma }_c^2/P$, where Γ_c is the linewidth of the passive cavity, n the number of photons in the lasing cavity mode and P the power produced by stimulated emission.

© 1990 Optical Society of America