Nonlinear optical properties of porous monoclinic BiVO4 at 2.3 µm for the passively Q-switching laser

In this work, we report the nonlinear optical response of porous monoclinic bismuth vanadate (m-BiVO4) at 2.3 µm for the first time. We adopted the conventional open/closed aperture (OA/CA) Z-scan techniques to systematically investigate the nonlinear optical (NLO) behavior. The effective nonlinear absorption coefficient βeff was −6.4 ± 0.02 cm MW−1, the nonlinear refractive index n2 was 9.88 ± 0.08 × 10-1 cm2 GW−1, and the NLO third-order susceptibility |χ(3)| was 2.69 × 10-7 esu. These NLO properties allowed it to be used as a fantastic saturable absorber for the generation of mid-infrared (MIR) pulses. As an application, we implemented a passively Q-switched Tm:YAP laser with the prepared porous m-BiVO4 saturable absorber for the first time. A minimum pulse duration of 349 ns and a maximum pulse repetition frequency of 193 kHz were achieved, resulting in a maximum pulse energy of 1.18 µJ. Our findings suggest that the porous m-BiVO4 could provide a route to the MIR optoelectronic applications.