Determination of the Nonlinear Optical Properties of Single- and Few-Layered Graphene Dispersions under Femtosecond Laser Excitation: Electronic and Thermal Origin Contributions
Michalis Stavrou, Ioannis Dalamaras, Νικόλαος Καραμπίτσος, Stelios Couris
Abstract
In the present work, the nonlinear optical properties of some single- and few-layered graphene dispersions under femtosecond laser excitation were studied using the Z-scan technique and are compared in order to evaluate the effect of the number of graphenic layers and the influence of the laser excitation conditions on the measurements. The experimental evidences obtained indicate that the nonlinear optical response of these graphenes’ dispersions under low repetition rate laser excitation conditions (i.e., 10 Hz) is several orders of magnitude lower than that reported using higher repetition rate laser excitation conditions (as e.g., kHz, MHz). To further investigate these experimental findings, Z-scan combined with a thermal lensing measurement technique was used to study the presence and the building of thermal/cumulative effects occurring under high repetition rate conditions. It was shown that thermal/cumulative effects were dominant, obscuring entirely the observation of the electronic origin nonlinear optical response. The contributions of both mechanisms were evaluated and unambiguously distinguished. To the best of our knowledge, this is the first work, investigating the nonlinear optical properties of single- and few-layered graphene, under low and high repetition rate laser excitation, providing a more accurate insight about the nonlinear optical response of graphene.