Ni-Doped Metal-Organic Frameworks as Nonlinear Optical Material Used in Saturable Absorption for Q-Switched Tm: YAP Laser

Metal-organic frameworks (MOFs) have received significant attention owing to their nanometer-sized void spaces, large surface areas, and tunable bandgaps. The properties of MOFs can be adjusted by doping other metal motifs or organic ligands. MOFs are widely employed in nanodevices and optical thin film materials; however, their third-order nonlinear optical (NLO) properties are rarely investigated, and their application in solid-state laser (SSL) has not been reported. In this paper, the NLO properties of Ni-doped MOFs are investigated comprehensively, wherein the value of the nonlinear refractive index and that of the real part of the third-order nonlinear optical susceptibility are obtained, i.e., 6.10 × 10−9 cm2/W and 6.20 × 10−7 esu, respectively. Consequently, an SSL that coupls Ni-doped MOFs with a saturable absorber (SA) is constructed. An average output power of 0.68/1.10 W is acquired with a 1.5% or 2.5% transmission of the output coupler (OC) under a passive Q-switch mode operation, corresponding to a per pulse energy of 6.29/10.90 μJ. When coupled with Tm: YAP, the as-constructed SSL exhibits a stable and short pulse (1.97 μs) at 1987.5 nm, indicating that Ni-doped MOFs can be applied to broadband SAs to achieve a fast photonic in the near-infrared spectra.