Upconversion processes, luminescence kinetics, and CW diode pumped 2.8 -μm laser action inEr doped double fluoride crystals

摘要

We studied theoretically and experimentally the luminescence decay from excited erbium levels and laser action at 2.8μm of lithium-yttrium double-fluoride LiYF_4:Er~(3+) (YLF:Er~(3+)) crystals. Experimental studies of the luminescence decay curves were carried out using selective laser excitation at ~4I_(13/2) level by Q-switch pulsed Yb-Er glass laser ( λ_(pump)=1.53μm). The spectroscopic model was developed to simulate the population kinetics of excited Er levels, emitting in VIS and IR spectral regions including the 3 μm laser transition levels in YLF:Er~(3+) crystals. The rate equations for the six lowest energy levels of YLF:Er~(3+) were numerically solved for short pulse excitation. It is shown the theoretical and experimental results are in good agreement. Single mode CW laser action at 2.8-μm was demonstrated in YLF:Er~(3+) and BaY_2F_8:Er~(3+) crystals under LD pumping for the first time. Output power as high as 0.32 W and slope efficiencies about 20% were obtained with YLF:Er~(3+) (10%) laser rod in longitudinal pump scheme. No spike structure was observed in output beam. The dependences of output power versus absorbed pump power were studied in laser rods with erbium concentrations 10 at.% using LD pumping module (Model DL-5M) with fiber output.