Localized plasmons formed in ultrathin metallic nanogaps can lead to robust absorption of incident light. Plasmonic metasurfaces based on this effect can efficiently generate energetic charge carriers, also known as hot electrons, owing to their ability to squeeze and enhance electromagnetic fields in confined subwavelength spaces. However, it is very challenging to accurately identify and quantify the dynamics of hot carriers, mainly due to their ultrafast time decay. Their nonequilibrium temperature response is one of the key factors missing to understand the short time decay and overall transient tunable absorption performance of gap-plasmon metasurfaces. Here, we systematically study the temperature dynamics of hot electrons and their transition into thermal carriers at various timescales from femto to nanoseconds by using the two-temperature model. Additionally, the hot electron temperature and generation rate threshold values are investigated by using a hydrodynamic nonlocal model approach that is more accurate when ultrathin gaps are considered. The derived temperature dependent material properties are used to study the ultrafast transient nonlinear modification in the absorption spectrum before plasmon-induced lattice heating is established leading to efficient tunable nanophotonic absorber designs. We also examine the damage threshold of these plasmonic absorbers under various pulsed laser illuminations, an important quantity to derive the ultimate input intensity limits that can be used in various emerging nonlinear optics and other tunable nanophotonic applications. The presented results elucidate the role of hot electrons in the response of gap-plasmon metasurface absorbers which can be used to design more efficient photocatalysis, photovoltaics, and photodetection devices.

中文翻译：

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揭示可调谐间隙等离子体超表面吸收器中的温度动力学和热电子产生

在超薄金属纳米间隙中形成的局部等离子体可以导致对入射光的强烈吸收。基于这种效应的等离子体超表面可以有效地产生高能电荷载流子，也称为热电子，因为它们能够在有限的亚波长空间中压缩和增强电磁场。然而，准确识别和量化热载流子的动力学非常具有挑战性，这主要是由于它们的超快时间衰减。它们的非平衡温度响应是了解间隙等离子体超表面的短时间衰减和整体瞬态可调谐吸收性能的关键因素之一。这里，我们通过使用双温度模型系统地研究了从飞秒到纳秒的不同时间尺度的热电子的温度动力学及其向热载体的转变。此外，通过使用流体动力学非局部模型方法研究热电子温度和生成速率阈值，当考虑超薄间隙时，该方法更准确。导出的与温度相关的材料特性用于研究在等离子激元诱导晶格加热建立之前吸收光谱中的超快瞬态非线性修改，从而实现有效的可调谐纳米光子吸收器设计。我们还检查了这些等离子体吸收体在各种脉冲激光照射下的损伤阈值，推导出最终输入强度极限的重要量，可用于各种新兴的非线性光学和其他可调谐纳米光子应用。所呈现的结果阐明了热电子在间隙等离子体超表面吸收剂响应中的作用，可用于设计更有效的光催化、光伏和光电检测装置。