Ebrahimpour Zeinab, Cojoc Dan, Principi Emiliano, Mincigrucci Riccardo
FERMI, Elettra-Sincrotrone Trieste, Area Science Park, Basovizza, 34149 Trieste, Italy.
CNR - Istituto Officina Dei Materiali, Area Science Park, Basovizza, 34149 Trieste, Italy.
J Synchrotron Radiat. 2025 Sep 1;32(Pt 5):1184-1193. doi: 10.1107/S1600577525005430. Epub 2025 Jul 21.
We present a technique based on the optical force of a femtosecond laser acting on liquid micro-droplets for their precise manipulation in a vacuum, enabling an efficient sample delivery system for soft X-ray experiments. Conventional liquid jet methods, which are utilized in soft X-ray experiments, consume large sample volumes and offer limited control over droplet trajectories, leading to significant sample waste. Our approach uses optical forces from a femtosecond-pulsed focused laser to deflect free-falling droplets, guiding them with high precision toward the interaction region. This significantly reduces sample waste while enabling real-time control over droplet positioning. To understand the behavior of droplets in vacuum and their interaction with the focused laser beam, we employ theoretical analysis and numerical simulations. Hertz-Knudsen equations describe the thermodynamics of free-falling and deflected droplets, allowing estimation of their temperature and size as a function of time and position. The optical force acting on the droplets is determined using the transfer matrix method and Lorenz-Mie theory. The proposed technique provides fine tuning over delivery time and thermodynamic properties of the liquid sample, offering a promising platform for investigating supercooled liquid micro-droplets and phase transitions. It is a particularly well suited liquid sample delivery method for ultrafast X-ray experiments using tabletop sources, as well as current and future free-electron laser and high harmonic generation facilities.
我们提出了一种基于飞秒激光对液体微滴的光力作用的技术，用于在真空中对其进行精确操控，从而实现一种用于软X射线实验的高效样品输送系统。在软X射线实验中使用的传统液体喷射方法会消耗大量样品体积，并且对液滴轨迹的控制有限，导致大量样品浪费。我们的方法利用飞秒脉冲聚焦激光产生的光力使自由下落的液滴偏转，将它们高精度地引导至相互作用区域。这显著减少了样品浪费，同时实现了对液滴定位的实时控制。为了理解真空中液滴的行为及其与聚焦激光束的相互作用，我们采用理论分析和数值模拟。赫兹 - 克努森方程描述了自由下落和偏转液滴的热力学，从而可以估计它们的温度和尺寸随时间和位置的变化。作用在液滴上的光力使用转移矩阵法和洛伦兹 - 米理论来确定。所提出的技术可对液体样品的输送时间和热力学性质进行微调，为研究过冷液体微滴和相变提供了一个有前景的平台。它是一种特别适合使用桌面光源的超快X射线实验以及当前和未来的自由电子激光及高次谐波产生设施的液体样品输送方法。
