Abstract

The unstable resonator belongs to the class of laser cavities that may possess excess spontaneous emission factor due to the nonorthogonal transverse modes. In this paper, we present results of an experimental study of the spontaneous emission factor in unstable-resonator semiconductor lasers. The spontaneous emission factor in an unstable-resonator laser having a convex mirror with 2-mm radius of curvature is measured to be 2 × 10⁻³, compared to 10⁻⁵ typical of a Fabry-Perot semiconductor laser of the same dimensions. The excess spontaneous emission factor results in multi-longitudinal-mode operation and damped relaxation oscillation. A linkage between the spontaneous emission factor, the cavity structure, and the longitudinal-mode spectra has been observed. In addition, we have observed a drastic reduction in the spontaneous emission factor, by as much as 2 orders of magnitude, due to the development of thermal wave-guiding.

© 1992 Optical Society of America