[en] Cobalt-doped magnesium aluminate spinel (Co:MgAl₂O₄) could be the most effective saturable absorber (SA) for Q-switching solid-state lasers operating at 1.5 μm. Using LiF as the sintering aid, highly transparent Co:MgAl₂O₄ ceramics were fabricated by hot pressing (HP) of the commercial spinel and the co-precipitated Co:MgAl₂O₄ powder mixture. The optical properties of Co:MgAl₂O₄ ceramics were investigated, and the ground state absorption cross section (σ_gas) of Co²⁺ was calculated from the curve of the absorption coefficient. For the Co:MgAl₂O₄ ceramics hot-pressed at 1600 °C for 2 h under 30 MPa with 1 wt.% LiF addition, the in-line transmittance reaches about 77% at 1000 nm and 1700 nm, and the ground state absorption cross section of Co²⁺ is 2.55 × 10⁻¹⁹ cm² at the wavelength of 1540 nm, which is promising as a saturable absorber for solid-state pulse laser operating at 1.5 μm. - Highlights: • Transparent Co:MgAl₂O₄ ceramics were fabricated by hot pressing with LiF addition. • The σ_gas of Co²⁺ in 0.05 at.% Co:MgAl₂O₄ ceramics is 2.55 × 10⁻¹⁹ cm² at 1540 nm. • Co:MgAl₂O₄ optical ceramics is a promising saturable absorber for 1.5 μm pulse laser.