Measurement of gain coefficient and resonator internal loss in Yb:YAG thin-disk-laser

In this paper, the gain coefficient and the resonator internal loss in quasi-three-level active medium lasers were measured by two different methods: the spectroscopic gain analysis (SGA) and generalized Findlay-Clay method (GFCM). Standard Findlay-Clay method was modified and formalized for quasi-three-level active medium lasers. With these methods, the gain coefficient and the resonator internal loss of a Yb:YAG thin-disk-laser (TDL) were obtained and the results were compared, analyzed and discussed. To verify the accuracy of these methods, a numerical code based on the laser rate equations was developed to simulate the cw operation of the TDL and predict the laser system parameters. The obtained values of the resonator internal loss from these methods were used in the simulation to calculate some laser parameters such as laser output power and gain of the active medium. The analyses of measured values showed that the results of SGA have better accuracy. The relative measurement errors of 1.2% and 18.4% for gain coefficient were obtained for SGA and GFCM, respectively.