Optical gain measurements with the amplified spontaneous emission technique.

An amplified spontaneous emission technique is described for the evaluation of optical gain as a function of the length of the pumped pencil-shaped area of the active medium. Continuous measurements of emission intensity are made while a movable screen varies the pumped length. Inhomogeneities of the pumping beam can be taken into account by employing two different pump intensities in alternate sequence. The system allows low-gain measurements minimizing the effect of pump intensity drifts, rf interferences, and efficiency loss of the active medium. In the presence of reabsorption the system suffers some modifications.