Investigation of a new laser active medium in the form of gadolinium scandium gallium garnet crystals activated with chromium and neodymium

A general method is proposed for calculating the populations of excited acceptor states when they interact with energy donors under conditions of nonradiative losses in the acceptor subsystem. The method is suitable for dealing with continuous and pulsed pumping and no restrictions are imposed on the shape of the pump pulses. A study is made of the time dependence of the population of the upper active level ⁴F_3/2 of Nd³⁺ in gadolinium scandium gallium garnet (GSGG) crystals containing chromium and neodymium. An allowance is made for energy migration in the donor subsystem in the case of low and high Nd³⁺ ion concentrations when, in the latter case, concentration self-quenching of Nd³⁺ is observed. A quantitative agreement is obtained between the calculated and experimental results and an increase in the population of the ⁴F_3/2 level of Nd³⁺ because of sensitization of the Nd³⁺ luminescence by Cr³⁺ ions is found. The proposed calculation method is used to determine the optimal concentrations of Nd³⁺ in GSGG:Cr:Nd crystals under continuous and pulsed lasing conditions.