Optical parametric amplification by two-dimensional semiconductors

Optical parametric amplification is a coherent mechanism whereby an optical signal is amplified by a pump via the generation of an idler field and it is the key ingredient of parametric oscillators. Here we demonstrate optical parametric amplification by monolayer transition-metal dichalcogenides, showing that amplification can be attained over a propagation through an atomic layer. The surface-like second-order nonlinear interaction bypasses phase-matching constraints, enabling ultrabroadband collinear amplification, generally unattainable due to material dispersion. Moreover, the amplification process is invariant over signal and pump in-plane polarizations. Our experimental findings pave the way for innumerable applications in nanophotonics and quantum information technology.