Nonlinear spectroscopy and passive Q-switching operation of a Co2+:LaMgAl11O19 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+:LaMgA(11)O(19) (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 T-4(2)(F-4) --> T-4(1)(P-4) optical transition and to transitions from the thermally populated E-2((2)G) excited state to doublet levels that arise from the F-2 free-ion level of the tetrahedrally coordinated Co2+ ion. Intensity-dependent transmission measurements were also carried out at 1.34 and 1.54 mu m. Passive Q switching of Nd3+:YAlO3 (1.34-mu m) and of Er3+:glass (1.54-mu m) 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. (C) 1999 Optical Society of America. [S0740-3224(99)01411-3].