Influence of gain distribution on the properties of unstable resonators.

It was first pointed out by Siegman (1) that the advantageous properties of unstable optical resonators include excellent transverse mode discrimination, large mode volumina, high beam quality and the possibility of solely using metal mirrors. It is these properties that make unstable optical resonator widely and successfully used for high power lasers. Further theoretical and experimental investigations on unstable optical resonators have been carried out by numerous authors (2,3,4,5,6). Most of them have been concentrating on the mode properties of passive resonators and the influence of inhomogeneous refraction index with the assumption that the gain is distributed homogeneously. However, in practice, the gain is not always homogeneously distributed and the gain distribution depends on e.g. the used pumping techniques and the uniformity of the electric field (7). To study the influence of gain distribution on the properties of unstable optical resonators, a program has been develope d which is based on the Fox and Li method. With this program the dependence of the output power as well as the beam quality of a laser with unstable resonators on the gain distribution has been studied. The result will be presented later. Experimental investigations have been made. The result corresponds to the theoretical results