Some features of laser excitation of ytterbium-erbium glasses

An analysis is made of some processes that occur under conditions of accumulation of population inversion due to the ⁴I_13/2–⁴I_15/2 resonant transition in Er³⁺ ions in ytterbium–erbium (Yb–Er) glasses of various compositions. Methods of measuring the parameters of direct and reverse excitation energy transfer between Er³⁺and Yb³⁺ ions are also studied. It is found that, under certain conditions achieved in practice, appreciable bleaching of the medium should be observed at the frequency of the pump radiation, particularly under conditions of high-intensity reverse transfer of excitation energy from Er³⁺ to Yb³⁺ ions. This is typical of glasses having a low rate of intracenter relaxation of Er³⁺ ions. It is also shown that nonsteady-state rate equations that assume a linear relationship between the rate of interionic transfer and the ground state population of the acceptor consistently describe the energy characteristics of the excitation processes of Yb–Er glasses. In this case, it is not necessary to introduce in the calculation model additional excitation losses that increase nonlinearly with the pump radiation.