Measurement of absorption cross sections of Co2+:MgAl2O4 crystals with transition of Co2+ ions along two orthogonal directions.

Abstract

The nonlinear transmission curves of the Co2+:MgAl2O4 crystal at 1.5 µm are experimentally measured by the pump-probe technique. The measurement results demonstrate that the transition into the near-infrared absorption band is polarized not only along the C3 local symmetry axis, but also along the direction perpendicular to the C3 axis, arising from the distortion of oxygen tetrahedrons about the Co2+ ions along the four C3 local symmetry axes. The obtained saturation curves are analyzed using a theoretical model taking into account the transition of Co2+ ions along two orthogonal directions. The ground-state absorption cross sections for polarization parallel and perpendicular to the C3 axis are calculated to be 3.4×10-19cm2 and 2.6×10-20cm2, respectively. The excited-state absorption cross section for polarization parallel to the C3 axis is estimated to be4.2×10-20cm2.