Functional graphene metamaterials by femtosecond laser reduction

Achieving broadband total light absorption of unpolarized light within a subwavelength ultrathin film is critical for optoelectronic applications such as photovoltaics, photodetectors, thermal emitters and optical modulators. Here we experimentally demonstrate a low-cost and scalable multilayer graphene ultra-broadband total light absorber of record-high 90% of unpolarized light absorption at near infrared wavelengths with a bandwidth of more than 300 nm. The thin metamaterial consists of alternating monolayer graphene and dielectric material prepared by a low-cost wet chemical layer-by-layer method. A simple grating is fabricated using flexible femtosecond laser writing that simultaneously removes the graphene in the ablated regions and converts the remaining graphene oxide to graphene via photo-reduction. Our results open a novel, flexible and viable approach to practical applications of nanostructured photonic devices based on 2D materials, which require strong absorption.