Excited state absorption and passive Q-switch performance of Co2+ doped oxide crystals

Abstract

Excited state absorption spectra (ESA) of the LiGa5O8 (LGO), MgAl2O4 (MALO) and LaMgAl11O19 (LMA) crystals doped with the tetrahedral Co2+ ion were studied under excitation at the 4A2→4T1(4F) transition. The ESA band was observed near 710–740 nm and assigned to the 4T2→4T1(4P) transition of the Co2+ ion. The lifetime of the 4T2 level of Co2+ ion at room temperature was estimated to be 130–350 ns depending on the crystal host. Absorption saturation measurements were performed and ground state and excited state absorption cross sections were estimated at the wavelengths of 1.34 and 1.54 μm. The crystals studied were used to Q-switch flashlamp-pumped 1.34 μm Nd3+:YAlO3 and 1.54 μm Er3+:glass lasers. Passive Q-switching of a diode pumped 1.35 μm Nd:KGd(WO4)2 laser was demonstrated using Co2+:MALO saturable absorber.