石墨烯纳米片悬浮液中Laser诱导微泡作为光限幅散射中心的光声识别
Photoacoustic Identification of Laser-induced Microbubbles as Light Scattering Centers for Optical Limiting in Liquid Suspension of Graphene Nanosheets
摘要：
碳纳米管、石墨烯和过渡金属二硫属化物的悬浮液在光限幅方面表现出优异的性能。然而，潜在的机制仍然难以捉摸，通常归因于其优越的非线性光学性质，如非线性吸收或非线性散射。使用石墨烯作为一个例子，我们表明，光热微泡是负责的光限幅作为强光散射中心：石墨烯片吸收入射光，并成为加热到水的沸点以上，导致蒸汽和微泡的产生。这一结论是基于对激光束上方气泡的直接观察以及激光诱导超声与光限幅之间的强相关性。石墨烯的原位拉曼散射进一步证实，在激光脉冲下石墨烯的温度升高到水的沸点以上，但仍然保持太低而不能蒸发石墨烯并产生石墨烯等离子体气泡。光热气泡散射不是一个非线性光学过程，需要非常低的激光强度。这种理解有助于我们设计更有效的光限幅材料，并了解纳米材料的内在非线性光学性质。
英文摘要：
Liquid suspensions of carbon nanotubes, graphene and transition metal dichalcogenides have exhibited excellent performance in optical limiting. However, the underlying mechanism has remained elusive and is generally ascribed to their superior nonlinear optical properties such as nonlinear absorption or nonlinear scattering. Using graphene as an example, we show that photo-thermal microbubbles are responsible for the optical limiting as strong light scattering centers: graphene sheets absorb incident light and become heated up above the boiling point of water, resulting in vapor and microbubble generation. This conclusion is based on direct observation of bubbles above the laser beam as well as a strong correlation between laser-induced ultrasound and optical limiting. In-situ Raman scattering of graphene further confirms that the temperature of graphene under laser pulses rises above the boiling point of water but still remains too low to vaporize graphene and create graphene plasma bubbles. Photo-thermal bubble scattering is not a nonlinear optical process and requires very low laser intensity. This understanding helps us to design more efficient optical limiting materials and understand the intrinsic nonlinear optical properties of nanomaterials.
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