Conformal Graphene Directly Synthesized on a Femtosecond Laser-Scribed In-Fiber Microstructure for High-Energy Ultrafast Optical Pulses.

Despite extensive efforts to explore femtosecond lasers functionalized by nonlinear graphene (Gf) that relies on the traditional transfer process, maximizing the efficiency, customizing the nonlinear interaction, and minimizing the optical loss remain critical challenges, especially in high-energy pulse generation. We demonstrate an ultrafast nonlinear all-fiber device based on conformal Gf directly synthesized in three dimensions on the surface of an in-fiber microstructure. A femtosecond laser-induced selective etching process is used to fabricate a customized microstructure that ensures the minimum but efficient laser-Gf interaction as well as possesses excellent surface conditions to suppress absorption and scattering loss. Conformal Gf is prepared by a spatial diffusion-based atomic carbon spraying process that enables nanocrystals to be synthesized homogeneously even onto the complex surface of the microstructure. The demonstration of high-energy pulses from the Gf saturable absorber highlights its simple, process-efficient, adjustable, and robust performance. The resultant hyperbolic secant pulses display individual pulse energy and peak power of up to 13.2 nJ and 20.17 kW, respectively.