Demetriou Giorgos, Bookey Henry T, Biancalana Fabio, Abraham Eitan, Wang Yu, Ji Wei, Kar Ajoy K
Opt Express. 2016 Jun 13;24(12):13033-43. doi: 10.1364/OE.24.013033.
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 cmW, approximately 8 orders of magnitude larger than any bulk dielectrics.
通过对单层石墨烯电导率进行理论分析，实验观测并明确验证了石墨烯中非线性折射的负值。采用Z扫描技术对多层石墨烯的非线性光学特性进行了实验研究。测量是在1150、1550、1900和2400纳米波长下，使用100飞秒激光源进行的。在激光照射下，多层石墨烯由于饱和吸收而呈现透射率增加，随后由于双光子吸收而出现光限幅现象。在工作波长范围内测量了饱和辐照度Isat和双光子吸收系数β。此外，还观测到了与辐照度相关的非线性折射，并将其与不依赖辐照度的传统非线性折射系数n2区分开来。所获得的与辐照度相关的非线性折射值约为10 cmW量级，比任何体电介质大约8个数量级。
