title: Nonlinear optical properties of multilayer graphene in the infrared.
abstract: A negative value for the nonlinear refraction in graphene is experimentally observed and unambiguously verified by performing a theoretical analysis arising from the conductivity of the graphene monolayer. The nonlinear optical properties of multi-layer graphene are experimentally studied by employing the Z-scan technique. The measurements are carried out at 1150, 1550, 1900 and 2400 nm with a 100-femtosecond laser source. Under laser illumination the multi-layer graphene exhibits a transmittance increase due to saturable absorption, followed by optical limiting due to two-photon absorption. The saturation irradiance Isat and the two-photon absorption coefficient β are measured in the operating wavelength range. Furthermore, an irradiance-dependent nonlinear refraction is observed and discriminated from the conventional nonlinear refraction coefficient n2,which is not irradiance dependent. The values obtained for the irradiance-dependent nonlinear refraction are in the order of ∼10-9cm2W-1, approximately 8 orders of magnitude larger than any bulk dielectrics.
authors.forename: Giorgos
authors.initials: G
authors.lastname: Demetriou
authors.forename: Henry T
authors.initials: HT
authors.lastname: Bookey
authors.forename: Fabio
authors.initials: F
authors.lastname: Biancalana
authors.forename: Eitan
authors.initials: E
authors.lastname: Abraham
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Ji
authors.forename: Ajoy K
authors.initials: AK
authors.lastname: Kar