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.