Saturable absorption and self-defocusing response of 2D monoelemental germanium nanosheets in broadband spectra.

Germanium has caused a research boom in recent years due to its high carrier mobility and good stability. Although germanium has been proven to have application potential in photodetectors and other fields, its nonlinear optical properties are rarely reported. Herein, we prepared 2D germanium nanosheets by liquid phase-exfoliation (LPE) method and studied its third-order nonlinear optical response. It is found that the germanium nanosheets exhibit a broadband nonlinear optical response such as it has a large nonlinear absorption coefficient αNL ≈ -0.87 cm GW-1 and a negative nonlinear refractive index n2 ≈ -6.30 × 10-13 cm2 W-1 at 1064 nm wavelength. The experimental results show the excellent nonlinear optical performance of germanium nanosheets and indicate that 2D germanium nanosheets have promising potential in a wide range of photonics device applications.