Cross relaxation in Tm-doped fiber lasers

Cross relaxation (CR) process in thulium ions is described. Performance of Tm-doped fiber lasers with different dopant concentrations is evaluated numerically with and without CR. Simulation shows that CR process can not only improve the slope efficiency and output of the laser system, but also lower the lasing threshold and extend the growth momentum of the laser performance. Backward LD-clad-pumped Tm-doped fiber lasers are built with Tm-doped fibers of different doping levels. A maximum output of 35.3W around 2μm is obtained with a slope efficiency of 47.2% from the 4.5wt.%- doped fiber laser while a higher slope efficiency of 54.1% was achieved from the 6.8wt.%-doped fiber laser. And, modeling shows that these laser systems are much more efficient than that without CR process.