Optical losses in YVO4 :RE (RE = Nd3+, Er3+, Tm3+) laser crystals

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO4:Nd and YVO4:Er is not significant except for that from the I-4(11/2) level of Er3+. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO4:Er laser slope efficiency when the Er3+ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the F-3(4)-H-3(6) laser operation near 1800 nm in the YVO4:Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks.