Nonlinear spectroscopy and passive Q-switching operation of a Co^2+ :LaMgAl_11O_19 crystal

A pump–probe technique with picosecond resolution was used to record and derive the differential and excited-state absorption (ESA) spectra of a Co2+:LaMgAl11O19 (LMA) single crystal in the visible and near-infrared spectral regions. Time resolution allowed us to observe ESA bands that can be assigned to a 4T2(4F)→4T1(4P) optical transition and to transitions from the thermally populated 2E(2G) excited state to doublet levels that arise from the 2F free-ion level of the tetrahedrally coordinated Co2+ ion. Intensity-dependent transmission measurements were also carried out at 1.34 and 1.54 µm. Passive Q switching of Nd3+:YAlO3 (1.34-µm) and of Er3+:glass (1.54-µm) lasers by use of the Co2+:LMA crystal as a saturable absorber was demonstrated. The pulse durations (energies) of the Q-switched Nd3+:YAlO3 and Er3+:glass lasers were found to be 75 ns (3.8 mJ) and 50 ns (4.5 mJ), respectively.