SPECTROSCOPIC AND STIMULATED EMISSION PROPERTIES OF Er-DOPED CRYSTALS FOR THREE-MICRON LASERS

Abstract
Based on spectroscopic data the various processes (energy transfers, excited state absorption) that influence the population dynamics of the excited levels in concentrated Er³⁺ doped laser crystals are discussed and their role in determining the population inversion between the ⁴I_11/2 and ⁴I_13/2 involved in three-micron laser emission is estimated by solving the laser rate equations for stationary regime under selective or non-selective pumping. The role of co-doping the crystals with ions that modify the mechanism of population of the initial laser level (such as Cr³⁺)or of ions that de-excite the terminal level (such as Nd³⁺, Tm³⁺ or Ho³⁺)is also discussed. It is thus shown that by a proper choice of the active medium and by correlation of the spectroscopic properties with the pump conditions a good control of the emission (wave length, regime of emission, efficiency and so on) could be obtained.