Theoretical Investigation of Saturable Absorption in Graphene

Abstract

The ultrafast saturable absorption of graphene has recently been studied intensively as graphene has been demonstrated as a promising saturable absorber. In this thesis, we applied a photodynamic model for quantitative explanations on the spectral dependence of saturation intensity in graphene in addition to the effects of graphene layer numbers and substrates. We found that the saturation intensity of graphene shows little dependence on its thickness, while the saturation depth is proportional to the number of layers of graphene. Moreover, the graphene placed on a substrate with higher refractive index (n2) saturates at higher intensity. It is also shown that the saturation depth of the graphene sample decreases as n2 increases. In the visible-near infrared spectral regions, we found that the saturation intensity of graphene decrease as the light wavelength increases. These theoretical findings are validated by a host of experiments on graphene samples produced by epitaxial method or exfoliation.