A pump–probe technique with picosecond resolution was used to record and derive the differential and excited-state absorption (ESA) spectra of a Co<sup>2+</sup>:LaMgAl<sub>11</sub>O<sub>19</sub> (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 <sup>4</sup>T<sub>2</sub>(<sup>4</sup>F)→ <sup>4</sup>T<sub>1</sub>(<sup>4</sup>P) optical transition and to transitions from the thermally populated <sup>2</sup>E(<sup>2</sup>G) excited state to doublet levels that arise from the <sup>2</sup>F free-ion level of the tetrahedrally coordinated Co<sup>2+</sup> ion. Intensity-dependent transmission measurements were also carried out at 1.34 and 1.54 µm. Passive <i>Q</i> switching of Nd<sup>3+</sup>:YAlO<sub>3</sub> (1.34-µm) and of Er<sup>3+</sup>:glass (1.54-µm) lasers by use of the Co<sup>2+</sup>:LMA crystal as a saturable absorber was demonstrated. The pulse durations (energies) of the <i>Q</i>-switched Nd<sup>3+</sup>:YAlO<sub>3</sub> and Er<sup>3+</sup>:glass lasers were found to be 75 ns (3.8 mJ) and 50 ns (4.5 mJ), respectively.
© 1999 Optical Society of America
K. V. Yumashev, I. A. Denisov, N. N. Posnov, V. P. Mikhailov, R. Moncorgé, D. Vivien, B. Ferrand, and Y. Guyot, "Nonlinear spectroscopy and passive Q-switching operation of a Co2+ :LaMgAl11O19 crystal," J. Opt. Soc. Am. B 16, 2189-2194 (1999)