Passively Q-switched Tm:CaLu_0.1Gd_0.9AlO₄ laser at 2 µm with hematite nanosheets as the saturable absorber

We report the first passive Q-switching operation at 1.95 µm utilizing the disordered Tm:CaLu_0.1Gd_0.9AlO₄ (Tm:CLGA) crystal and the hematite (α-Fe₂O₃) nanosheets as the saturable absorber. The nonlinear saturable absorption properties of the hematite nanosheets were investigated by the conventional Z-scan technology. The modulation depth of 14.3% with the low saturation intensity of 205 kW/cm2 was obtained, indicating that the hematite could be a suitable saturable absorber for the mid-infrared pulse generation. Using the disordered Tm:CLGA crystal as the gain medium, the passive Q-switching operation could be realized with the hematite nanosheets as the saturable absorber, producing the shortest pulse duration of 402 ns with a repetition rate of 76 kHz. The experimental results convinced us that the hematite nanosheets could be of great interest in the optical pulse generation in the mid-infrared region.