Enhanced Nonlinear Optical Responses in MoS2 via Femtosecond Laser-Induced Defect-Engineering

2D materials are a promising platform for applications in many fields as they possess a plethora of useful properties that can be further optimized by careful engineering, for example, by defect introduction. While reliable high-yield defect engineering methods are in demand, most current technologies are expensive, harsh, or non-deterministic. Optical modification methods offer a cost-effective and fast mechanism to engineer the properties of 2D materials at any step of the device fabrication process. In this paper, the nonlinear optical responses of mono-, bi-, and trilayer molybdenum disulfide (MoS2) flakes are enhanced by deterministic defect-engineering with a femtosecond laser. A 50-fold enhancement in the third harmonic generation (THG) and a 3.3-fold increase in the second harmonic generation (SHG) in the optically modified areas is observed. The enhancement is attributed to resonant SHG and THG processes arising from optically introduced mid-band gap defect states. These results demonstrate a highly controllable, sub-micrometer resolution tool for enhancing the nonlinear optical responses in 2D materials, paving the way for prospective future applications in optoelectronics, quantum technologies, and energy solutions.