Er:YAG three-micron laser: performances and limits

Mathematical modeling is used to estimate the performances of the three-micron Er:YAG laser in various generation regimes. The model, based on simple rate equations, uses exclusively spectroscopic data and includes upconversion from both initial (/sup 4/I/sub 11/2/) and terminal (/sup 4/I/sub 13/2/) levels as well as the cross-relaxation from the pump level (/sup 4/S/sub 3/2/). Despite the unfavorable ratio between the lifetimes of the laser levels, the recirculation of the excitation on the metastable levels produced by the effective energy transfer processes at high erbium concentrations leads to rather high emission efficiency in the continuous wave (CW) regime. In contrast, in the Q-switch regime, the energy transfer processes are practically frozen during the giant pulse generation and the access to the stored energy is limited. In this paper, simple analytical expressions for emission efficiency in CW and Q-switch regimes are presented. Due to the growing interest in short laser pulses for medical applications, we discuss in more detail the Q-switch regime (pump conditions, co-doping, etc.).