Laser-produced plasmas (LPPs) engulf exotic and complex conditions ranging in temperature, density, pressure, magnetic and electric fields, charge states, charged particle kinetics, and gas-phase reactions based on the irradiation conditions, target geometries, and background cover gas. The application potential of the LPP is so diverse that it generates considerable interest for both basic and applied research areas. The fundamental research on LPPs can be traced back to the early 1960s, immediately after the invention of the laser. In the 1970s, the laser was identified as a tool to pursue inertial confinement fusion, and since then several other technologies have emerged out of LPPs. These applications prompted the development and adaptation of innovative diagnostic tools for understanding the fundamental nature and spatiotemporal properties of these complex systems. Although most of the traditional characterization techniques developed for other plasma sources can be used to characterize the LPPs, care must be taken to interpret the results because of their small size, transient nature, and inhomogeneities. The existence of the large spatiotemporal density and temperature gradients often necessitates nonuniform weighted averaging over distance and time. Among the various plasma characterization tools, optical-based diagnostic tools play a key role in the accurate measurements of LPP parameters. The optical toolbox contains optical spectroscopy (emission, absorption, and fluorescence), as well as passive and active imaging and optical probing methods (shadowgraphy, Schlieren imaging, interferometry, Thomson scattering, deflectometry, and velocimetry). Each technique is useful for measuring a specific property, and its use is limited to a certain time span during the LPP evolution because of the sensitivity issues related to the selected measuring tool. Therefore, multiple diagnostic tools are essential for a comprehensive insight into the entire plasma behavior. Recent improvements in performance in laser and detector systems have expanded the capability of the aforementioned passive and active diagnostic tools. This review provides an overview of optical diagnostic tools frequently employed for the characterization of the LPPs and emphasizes techniques, associated assumptions, and challenges. Considering that most of the industrial and other applications of the LPP belong to low to moderate laser intensities (${10}^8–{10}^{15}{\mathrm{W}\mathrm{cm}}^{-2}$), this review focuses on diagnostic tools pertaining to this regime.

中文翻译：

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激光产生的等离子体的光学诊断

激光产生的等离子体 (LPP) 涵盖了基于辐照条件、目标几何形状和背景覆盖气体的奇异且复杂的条件，包括温度、密度、压力、磁场和电场、电荷状态、带电粒子动力学和气相反应。 LPP 的应用潜力如此广泛，以至于它引起了基础和应用研究领域的极大兴趣。 LPP 的基础研究可以追溯到 20 世纪 60 年代初，即激光发明之后。 20 世纪 70 年代，激光被认为是实现惯性约束聚变的工具，从那时起，LPP 中又出现了其他几种技术。这些应用促进了创新诊断工具的开发和适应，以了解这些复杂系统的基本性质和时空特性。虽然为其他等离子体源开发的大多数传统表征技术可用于表征 LPP，但由于其尺寸小、瞬态性质和不均匀性，必须小心解释结果。大时空密度和温度梯度的存在通常需要在距离和时间上进行非均匀加权平均。在各种等离子体表征工具中，基于光学的诊断工具在 LPP 参数的精确测量中发挥着关键作用。光学工具箱包含光谱（发射、吸收和荧光），以及被动和主动成像和光学探测方法（阴影摄影、纹影成像、干涉测量、汤姆逊散射、偏转测量和测速）。每种技术都可用于测量特定属性，并且由于与所选测量工具相关的敏感性问题，其使用仅限于 LPP 演进过程中的特定时间跨度。因此，多种诊断工具对于全面了解整个等离子体行为至关重要。激光和探测器系统性能的最新改进扩展了上述被动和主动诊断工具的能力。本综述概述了常用于表征 LPP 的光学诊断工具，并强调了技术、相关假设和挑战。考虑到 LPP 的大多数工业和其他应用都属于低到中等激光强度（${10}^8–{10}^{15}{\mathrm{瓦}\mathrm{厘米}}^{-2}$），本次审查重点关注与该制度相关的诊断工具。