Upconversion rate in Nd-doped Ta2O5 waveguides and influence on the cw laser performance

The non-linear upconversion processes in Nd-doped Ta2O5 waveguides have been investigated to determine the depopulation rate of the 4F3/2 laser level due to energy transfer upconversion (ETU). A rate-equation analysis has been used to obtain analytical expressions of the population and average lifetime of the 4F3/2 level under modulated cw excitation. The analysis of lifetime measurements as a function of excitation power yielded to an ETU rate of about 22 800 s−1. Equations for the four level cw laser performance have been obtained using a rate-equation approximation that includes ETU processes. The effect of upconversion on the laser performance has been estimated using the parameters obtained for the Nd-doped Ta2O5 waveguide lasers.