  We demonstrate greatly enhanced light absorption by monolayer graphene over a
broad spectral range, from visible to near infrared, based on the attenuated
total reflection. In the experiment, graphene is sandwiched between two
dielectric media referred as superstrate and substrate. Based on numerical
calculation and experimental results, the closer the refractive indices of the
superstrate and the substrate, the higher the absorption of graphene will be.
The light absorption of monolayer graphene up to 42.7% is experimentally
achieved.
