Analysis of the laser performance of Tm~(3+), Tb~(3+) (Ho~(3+)):YVO_4 crystals at ～1.5 μm wavelength

摘要

The absorption spectra of Tb,Tm:YVO_4 and Ho,Tm:YVO_4 are measured. The radiant and non-radiant transition probabilities from higher level to lower level, A_(i,j) and ω_(i,j), and the cross-relaxation probability are calculated in virtue of Judd-Ofelt and Dexter theories. The fluorescence lifetime of Tm~(3+) in the Tb~(3+) (or Ho~(3+)) co-doped crystal is calculated. It indicates that the lifetime of initial level ~3H_4 of the laser transition can be shorter than that of terminal level ~3F_4 of the transition if the atomic percentage of Tb~(3+) (or Ho~(3+)) ions is bigger than about 1 at%: namely, by means of the co-doping Tb~(3+) (or Ho~(3+)) ions the self-termination phenomenon of laser light can be eliminated. Inserting the optic parameters to the formula deduced here on the laser threshold power P_(th)~(4) and the slope efficiency η_s~(4) of the four-energy-level system, we obtain the relationship of threshold power P_(th)~(4) to the concentration of Tm~(3+) ions and discuss the effect of Tb~(3+) (or Ho~(3+)) ion concentration on the laser threshold power P_(th)~(4) around 1.5 μm wavelength. The result shows that Tb,Tm:YVO_4 crystal is a better choice to make the laser at t～1.5 μm wavelength than Ho,Tm:YVO_4 crystal. We give the appropriate composition of (1―2) at% Tb, (1―2) at% Tm:YVO_4, just for reference.