Spectral compression using holographie two-wave mixing

Abstract

An ideal laser emits coherent radiation which has a δ-function spectral distribution. Such coherent radiation contains only single-frequency components. In practice, however, a laser emits a quasi-monochromatic radiation which contains a finite spread in its frequency distribution. This frequency spread can be due to spontaneous emission, multi-longitudinal mode operation, as well as other perturbations. Depending on the quality of the laser, this finite spread can range anywhere from zero to multigigahertz.