Simple technique for measuring the energy-transfer-upconversion parameter in solid-state laser materials

This paper describes an alternative and easier method for measuring the upconversion parameter based on measuring laser threshold pump power as a function of resonator loss. This approach exploits the fact that upconversion loss is larger for higher excitation densities and that the excitation density in a laser can be increased by simply increasing the resonator loss. An analytical model is developed for the dependence of threshold pump power, P_pth on the upconversion parameter and the resonator loss for both four-level and quasi-three-level lasers.