Yb 3+ to Er 3+ energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca 2Al 2SiO 7

Abstract

Rate equations formalism is used to predict the population ratio of the Er 3+ 4 I 13 2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er 3+ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10 −16 and 0.45 x 10 −16 cm 3 s −1, respectively. Attempts of codoping the system with Nd 3+, Eu 3+ and Ce 3+ have been realised in order to increase the population of the Er 3+ 4 I 13 2 laser emitting level. Best results are obtained with Ce 3+ ion since in the sample containing 6 x 10 20 Ce 3+/cm 3, the Er 3+ 4 I 11 2 level lifetime is divided by a factor of 3 while the Er 3+ 4 I 13 2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd 3+ or Eu 3+ ions simultaneously decreases the Er 3+ 4 I 11 2 and 4 I 13 2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.