We experimentally determined the dispersion of third-order optical susceptibility χ(3) of graphene oxide (GO) in the visible region (450 - 750 nm) by combining spectroscopic ellipsometry and ultrafast pump and probe spectroscopy in the femtosecond regime. In order to mitigate the damage of wide-spectrum laser to photonic devices, GO has become a promising material for optical limiting (OL) devices. However, there is no report about the χ(3) dispersion of GO, which is a complex quantity that directly corresponds to nonlinear refraction and absorption and is a crucial parameter for the manipulation and application of its OL properties. Here, we identified that the linear optical response of GO shows a flat dispersion in the visible region. In contrast, its nonlinear optical response exhibits saturable absorption (SA) at the short wavelength and reverse saturable absorption (RSA) at the long wavelength. These results propel the application of GO in the broadband OL devices based on the RSA behavior. In addition, by controlling the fraction of sp2 and sp3 hybridizations, it also provides opportunities to tailor the NLO properties and OL performance of GO.

中文翻译：

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氧化石墨烯三阶光学磁化率的实验色散

我们通过在飞秒范围内结合光谱椭偏仪和超快泵浦和探针光谱，通过实验确定了氧化石墨烯 (GO) 在可见光区 (450 - 750 nm) 中的三阶光学磁化率 χ(3) 的色散。为了减轻宽光谱激光对光子器件的损伤，GO已成为一种有前途的光学限制（OL）器件材料。然而，没有关于 GO 的 χ(3) 色散的报道，它是一个复数，直接对应于非线性折射和吸收，是其 OL 特性的操纵和应用的关键参数。在这里，我们发现 GO 的线性光学响应在可见光区域显示出平坦的色散。相比之下，其非线性光学响应在短波长表现出饱和吸收 (SA)，在长波长表现出反饱和吸收 (RSA)。这些结果推动了 GO 在基于 RSA 行为的宽带 OL 设备中的应用。此外，通过控制 sp2 和 sp3 杂交的比例，它还提供了定制 GO 的 NLO 特性和 OL 性能的机会。