Passively Q-switched near-infrared lasers with bismuthene quantum dots as the saturable absorber

摘要： Bismuthene quantum dots (Bi-QDs) were synthesized via the liquid phase exfoliation (LPE) method for the passive Q-switching operation in near-infrared (NIR) region. The nonlinear optical properties of the prepared Bi-QDs were investigated by the open-aperture Z-scan technology. The modulation depths were 18.1% and 5.1% at 1.06 and 1.34 μm, respectively. Based on the Bi-QDs saturable absorber, passively Q-switched Nd:GdVO4 lasers operating at 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2 transitions were demonstrated, showing the wideband optical modulation in NIR regime. For the 4F3/2 → 2I13/2 transition lasing at 1.34 μm, the shortest pulse duration of 155 ns was obtained with a repetition rate of 457 kHz. With respect to the 4F3/2 → 2I11/2 transition at 1.06 μm, the minimum pulse duration was 150 ns with a repetition rate of 424 kHz, leading to a single pulse energy of 261 nJ and a peak power of 1.68 W. In addition, the ground state absorption cross section and the excited state absorption cross section of Bi-QDs were also investigated for the ?rst time. The impact of the excited state lifetime on the output parameters was numerically stimulated by the coupled rate equations. Our work con-?rmed that the trap state in Bi-QDs played an important role in the pulse generation mechanism.