Mishra Yogeshwar Nath, Wang Peng, Bauer Florian J, Zhang Yide, Hanstorp Dag, Will Stefan, Wang Lihong V
Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical Engineering, Department of Electrical Engineering, California Institute of Technology, 1200 East California Boulevard, Mail Code 138-78, Pasadena, CA, 91125, USA.
NASA-Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA.
Light Sci Appl. 2023 Feb 21;12(1):47. doi: 10.1038/s41377-023-01095-5.
Unburnt hydrocarbon flames produce soot, which is the second biggest contributor to global warming and harmful to human health. The state-of-the-art high-speed imaging techniques, developed to study non-repeatable turbulent flames, are limited to million-frames-per-second imaging rates, falling short in capturing the dynamics of critical species. Unfortunately, these techniques do not provide a complete picture of flame-laser interactions, important for understanding soot formation. Furthermore, thermal effects induced by multiple consecutive pulses modify the optical properties of soot nanoparticles, thus making single-pulse imaging essential. Here, we report single-shot laser-sheet compressed ultrafast photography (LS-CUP) for billion-frames-per-second planar imaging of flame-laser dynamics. We observed laser-induced incandescence, elastic light scattering, and fluorescence of soot precursors - polycyclic aromatic hydrocarbons (PAHs) in real-time using a single nanosecond laser pulse. The spatiotemporal maps of the PAHs emission, soot temperature, primary nanoparticle size, soot aggregate size, and the number of monomers, present strong experimental evidence in support of the theory and modeling of soot inception and growth mechanism in flames. LS-CUP represents a generic and indispensable tool that combines a portfolio of ultrafast combustion diagnostic techniques, covering the entire lifecycle of soot nanoparticles, for probing extremely short-lived (picoseconds to nanoseconds) species in the spatiotemporal domain in non-repeatable turbulent environments. Finally, LS-CUP's unparalleled capability of ultrafast wide-field temperature imaging in real-time is envisioned to unravel mysteries in modern physics such as hot plasma, sonoluminescence, and nuclear fusion.
未燃尽的碳氢化合物火焰会产生烟灰，这是全球变暖的第二大元凶，且对人体健康有害。为研究不可重复的湍流火焰而开发的先进高速成像技术，成像速率限制在每秒百万帧，在捕捉关键物种的动态方面有所不足。不幸的是，这些技术无法完整呈现对理解烟灰形成至关重要的火焰 - 激光相互作用。此外，多个连续脉冲引起的热效应会改变烟灰纳米颗粒的光学特性，因此单脉冲成像至关重要。在此，我们报告了用于火焰 - 激光动力学每秒十亿帧平面成像的单次激光片压缩超快摄影（LS - CUP）。我们使用单个纳秒激光脉冲实时观测到了激光诱导的白热发光、弹性光散射以及烟灰前体——多环芳烃（PAHs）的荧光。PAHs发射、烟灰温度、初级纳米颗粒尺寸、烟灰聚集体尺寸以及单体数量的时空图，为火焰中烟灰起始和生长机制的理论及模型提供了有力的实验证据。LS - CUP是一种通用且不可或缺的工具，它结合了一系列超快燃烧诊断技术，涵盖烟灰纳米颗粒的整个生命周期，用于在不可重复的湍流环境中探测时空域内极短寿命（皮秒到纳秒）的物种。最后，LS - CUP无与伦比的实时超快宽场温度成像能力有望揭开现代物理学中诸如热等离子体、声致发光和核聚变等奥秘。
