We report on [Formula: see text]-scan investigations of the nonlinear optical properties of thin pyrolytic carbon films and two- and three-layer graphene films, utilizing an 800[Formula: see text]nm pulsed laser generating ultrashort 180[Formula: see text]fs pulses. We analyze the sign and magnitude of nonlinear refraction and absorption in these materials, given contradictory results in this respect in the literature. In particular, we find that nonlinear refraction of graphene changes sign with changing light intensity with concomitant subtle changes in nonlinear absorption, a behavior not reported previously that suggests an interplay of several mechanisms that depend on intensity. Pyrolytic carbon films, on the contrary, exhibit positive refraction, whose magnitude (nonlinear refractive index [Formula: see text][Formula: see text]cm2/W) is comparable to that of graphene, and strong negative absorption, i.e., bleaching, contrary to previously reported results. We discuss implications and possible mechanisms of the observed phenomena.

中文翻译：

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石墨烯和热解碳的非线性光学性质：比较研究

我们报告了[公式：见文本]-利用 800 [公式：见文本]nm 脉冲激光产生超短 180 [公式：见文本]fs 脉冲。我们分析了这些材料中非线性折射和吸收的符号和大小，在文献中给出了这方面的矛盾结果。特别是，我们发现石墨烯的非线性折射随着光强度的变化而变化，伴随着非线性吸收的细微变化，这种行为以前没有报道过，表明依赖于强度的几种机制的相互作用。相反，热解碳膜表现出正折射，其大小（非线性折射率[公式：见正文][公式：见正文]cm2/W) 与石墨烯相当，并且具有很强的负吸收，即漂白，与先前报道的结果相反。我们讨论了观察到的现象的含义和可能的机制。