Understanding the collaborative behaviors of the excitons and phonons that result from light–matter interactions is important for interpreting and optimizing the underlying fundamental physics at work in devices made from atomically thin materials. In this study, the generation of exciton‐coupled phonon vibration from molybdenum disulfide (MoS₂) nanosheets in a pre‐excitonic resonance condition is reported. A strong rise‐to‐decay profile for the transient second‐harmonic generation (TSHG) of the probe pulse is achieved by applying substantial (20%) beam polarization normal to the nanosheet plane, and tuning the wavelength of the pump beam to the absorption of the A‐exciton. The time‐dependent TSHG signals clearly exhibit acoustic phonon generation at vibration modes below 10 cm⁻¹ (close to the Γ point) after the photoinduced energy is transferred from exciton to phonon in a nonradiative fashion. Interestingly, by observing the TSHG signal oscillation period from MoS₂ samples of varying thicknesses, the speed of the supersonic waves generated in the out‐of‐plane direction (Mach 8.6) is generated. Additionally, TSHG microscopy reveals critical information about the phase and amplitude of the acoustic phonons from different edge chiralities (armchair and zigzag) of the MoS₂ monolayers. This suggests that the technique could be used more broadly to study ultrafast physics and chemistry in low‐dimensional materials and their hybrids with ultrahigh fidelity.

中文翻译：

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MoS2纳米片超快载流子动力学的瞬态SHG成像

理解由光-物质相互作用引起的激子和声子的协同行为，对于解释和优化由原子薄材料制成的设备在工作中的基本物理原理很重要。在这项研究中，据报道在激子共振之前，由二硫化钼（MoS ₂）纳米片产生的激子耦合声子振动。通过施加垂直于纳米片平面的大量（20％）光束偏振并将泵浦光束的波长调整到吸收波长，可实现探测脉冲的瞬态二次谐波（TSHG）的强上升到衰减曲线激子的 随时间变化的TSHG信号在振动模式低于10 cm ^-1时清楚地显示出声子产生在光致能量以非辐射方式从激子转移到声子后（接近Γ点）。有趣的是，通过观察厚度不同的MoS ₂样本的TSHG信号振荡周期，可以产生沿平面外方向（马赫数8.6）产生的超声波的速度。此外，TSHG显微镜还从MoS ₂单层的不同边缘手性（扶手椅和之字形）中揭示了有关声子的相位和幅度的关键信息。这表明该技术可以更广泛地用于研究低维材料及其具有超高保真度的杂化材料的超快物理学和化学。