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 C o 2 + : M g A l 2 O 4 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 C 3 local symmetry axis, but also along the direction perpendicular to the C 3 axis, arising from the distortion of oxygen tetrahedrons about the C o 2 + ions along the four C 3 local symmetry axes. The obtained saturation curves are analyzed using a theoretical model taking into account the transition of C o 2 + ions along two orthogonal directions. The ground-state absorption cross sections for polarization parallel and perpendicular to the C 3 axis are calculated to be 3.4 × 10 − 19 c m 2 and 2.6 × 10 − 20 c m 2 , respectively. The excited-state absorption cross section for polarization parallel to the C 3 axis is estimated to be 4.2 × 10 − 20 c m 2 .