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

The nonlinear transmission curves of the Co2+ : MgAl2O4 crystal at 1.5 mu m 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 Co2+ 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 Co2+ 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 x 10(-19) cm(2) and 2.6 x 10(-20) cm(2), respectively. The excited-state absorption cross section for polarization parallel to the C-3 axis is estimated to be 4.2 x 10(-20) cm(2). (C) 2022 Optica Publishing Group