Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309-0440, USA.
Rev Sci Instrum. 2023 Mar 1;94(3):033001. doi: 10.1063/5.0127119.
High harmonic generation (HHG) makes it possible to measure spin and charge dynamics in materials on femtosecond to attosecond timescales. However, the extreme nonlinear nature of the high harmonic process means that intensity fluctuations can limit measurement sensitivity. Here we present a noise-canceled, tabletop high harmonic beamline for time-resolved reflection mode spectroscopy of magnetic materials. We use a reference spectrometer to independently normalize the intensity fluctuations of each harmonic order and eliminate long term drift, allowing us to make spectroscopic measurements near the shot noise limit. These improvements allow us to significantly reduce the integration time required for high signal-to-noise (SNR) measurements of element-specific spin dynamics. Looking forward, improvements in the HHG flux, optical coatings, and grating design can further reduce the acquisition time for high SNR measurements by 1-2 orders of magnitude, enabling dramatically improved sensitivity to spin, charge, and phonon dynamics in magnetic materials.
高次谐波产生（HHG）使得在飞秒到阿秒时间尺度上测量材料中的自旋和电荷动力学成为可能。然而，高次谐波过程的极端非线性性质意味着强度波动可能会限制测量的灵敏度。在这里，我们提出了一种用于时间分辨反射模式磁性材料光谱学的消噪、台式高次谐波光束线。我们使用参考光谱仪独立地对每个谐波阶的强度波动进行归一化，并消除长期漂移，从而使我们能够在接近散粒噪声极限的条件下进行光谱测量。这些改进使得我们能够显著减少对特定元素自旋动力学的高信噪比（SNR）测量所需的积分时间。展望未来，高次谐波通量、光学涂层和光栅设计的改进可以将高 SNR 测量的采集时间进一步减少 1-2 个数量级，从而极大地提高对磁性材料中自旋、电荷和声子动力学的灵敏度。
