Nonlinear Absorption of Submicrometer Grain‐Size Cobalt‐Doped Magnesium Aluminate Transparent Ceramics

Transparent cobalt‐doped magnesium aluminate spinel ( Co : MgAl 2 O 4 ) ceramics with a submicrometer grain size were prepared by spark plasma sintering. For the first time, the nonlinear absorption of Co : MgAl 2 O 4 transparent ceramics was experimentally demonstrated. Both ground state absorption (σ GSA ) and excited state absorption (σ ESA ) were estimated using the solid‐state slow saturable absorber model based on absorption saturation measurements performed at 1.535 μm. σ GSA and σ ESA for 0.03 at.% Co : MgAl 2 O 4 were found to be 4.1 × 10 −19  cm 2 and 4.0 × 10 −20  cm 2 , respectively. In the case of 0.06 at.% Co : MgAl 2 O 4 ceramics, σ GSA = 2.6 × 10 −19  cm 2 and σ ESA = 5.3 × 10 −20  cm 2 were determined.