2D materials such as graphene and transition metal dichalcogenides (TMDCs) can be layered together in many configurations to create van-der-Waals (vdW) heterostructures. Within these heterostructures, the optical and electrical properties are influenced by interlayer coupling. Because graphene and MoS₂ have complementary properties, vdW heterostructures composed of these two materials have been shown to be useful for optoelectronic devices.

Baitao Zhang, Yanlu Li, and colleagues, Shandong University, China, have used density functional theory (DFT) calculations to find the theoretical optimal thickness and layering of a graphene-MoS₂ heterostructure for use in lasers. The layer thickness influences the interlayer coupling. The team then synthesized the heterostructures using chemical vapor deposition (CVD) and used them as saturable absorbers in a femtosecond solid-state laser.

The researchers found that heterostructures composed of one to four layers of MoS₂ were the most efficient. The thickness of MoS₂ in the heterostructure affects the nonlinear optical response. The prepared vdW heterostructures have work functions between 4.63 and 5.00 eV. When the heterostructures were incorporated into a laser, it achieved pulses as short as 236 fs and an output power of 0.55 W. According to the researchers, these are the best results ever achieved with a heterostructure-based mode-locked laser.

• Tunable Ultrafast Nonlinear Optical Properties of Graphene/MoS₂ van der Waals Heterostructures and Their Application in Solid-State Bulk Lasers,
  Xiaoli Sun, Baitao Zhang, Yanlu Li, Xingyun Luo, Guoru Li, Yanxue Chen, Chengqian Zhang, Jingliang He,
  ACS Nano 2018.
  https://doi.org/10.1021/acsnano.8b06236