The probing of coherent lattice vibrations in solids has been conventionally carried out using time-resolved transient spectroscopy where only the relative oscillation amplitude can be obtained. Using time-resolved X-ray techniques, absolute electron-phonon coupling strength could be extracted. However, the complexity of such an experiment renders it impossible to be carried out in conventional laboratories. Here we demonstrate that the electron-phonon, anharmonic phonon-phonon coupling, and their relaxation dynamics can be probed in real-time using high-harmonic spectroscopy. Our technique is background-free and has extreme sensitivity directly in the energy domain. In combination with the optical deformation potential calculated from density functional perturbation theory and the absolute energy modulation depth, our measurement reveals the maximum displacement of neighboring oxygen atoms in α-quartz crystal to tens of picometers in real space. By employing a straightforward and robust time-windowed Gabor analysis for the phonon-modulated high-harmonic spectrum, we successfully observe channel-resolved four-phonon scattering processes in such highly nonlinear interactions. Our work opens a new realm for accurate measurement of coherent phonons and their scattering dynamics, which allows for potential benchmarking ab-initio calculations in solids
Two-color harmonic spectroscopy of ultrafast Dirac electron dynamics
Technion – Israel Institute of Technology（以色列理工学院）；Guangdong Technion – Israel Institute of Technology（广东以色列理工学院）；Eastern Institute of Technology（东方理工）
Extreme Ultraviolet Time- and Angle-Resolved Photoemission Spectroscopy with 21.5 meV Resolution using High-Order Harmonic Generation from a Turn-Key Yb:KGW Amplifier
表征和控制量子材料的电子性质需要在动量空间的大区域上直接测量非平衡电子能带结构。在这里，我们展示了一个实验装置的时间和角度分辨的光电子能谱使用高次谐波探测脉冲产生的一个强大的，中等高功率（20 W）Yb：KGW放大器与可调重复频率在50和150 kHz之间。通过驱动高次谐波产生（HHG）的基本1025 nm的激光脉冲的二次谐波，我们表明，在21.8 eV的光子能量的单谐波探测脉冲可以有效地隔离，而不使用单色器。在50 kHz下，靶上光子通量可以达到5 x 10^10光子/秒，并且测量的时间分辨率为320 fs。Yb驱动的HHG源的相对较长的脉冲持续时间使我们能够达到21.5 meV的优异能量分辨率，这是通过在150 kHz的较高重复率下使用1.5 x 10^8光子/秒的低光子通量抑制空间电荷展宽来实现的。通过测量拓扑半金属ZrSiS和拓扑绝缘体Sb 2-xGdxTe 3的设置的能力证明。
