Extraction efficiency and thermal lensing in Tm: YAG lasers

Abstract

We model and compare with experiment the threshold, extraction efficiency and temperature effects in Tm:YAG lasers. In particular, we are concerned with high pump powers where lasing can cease abruptly. We simulate the pump depletion equation with the forward and reverse lasing equations combined with the CW rate equations which include cross-relaxation. The resonator is single-pass, end-pumped Fabry-Perot. Consequently, the equations must be solved numerically with a shooter. Our simulation of these equations gives the z-dependence of the intensities, of the populations and of the heat source. Heating is created by nonradiative decay from the two upper manifolds and by the cross-relaxation energy deficit. This leads to thermal lensing as a function of incident pump power which causes lasing shut-off as the resonator becomes unstable. Our simulations for the slope efficiency, threshold and laser shut-off agree with experiment. Additionally, we show that for pump powers in the range of 15–20 W the core temperature rise is about 40 K and the thermal focal length is in the range 5–6 cm.