标题： 压缩超快摄影揭示了由密集气体激光击穿形成的等离子体内部过程在早期阶段占主导地位 显示英文标题

标题： Compressed Ultrafast Photography of Plasmas Formed from Laser Breakdown of Dense Gases Reveals that Internal Processes Dominate Evolution at Early Times

摘要： 压缩超快摄影（CUP）应用于氩气和氙气在高达40atm压力下的激光击穿，以获得单次事件的等离子体动力学二维图像，空间分辨率为250x100像素，等效帧率500 GHz。 通过红、绿、蓝和宽频带滤波器测量光发射随位置和时间的变化。 通常用于CUP的空间编码和时间剪切图像现在通过引入由空间积分和时间剪切未编码信号给出的约束得到增强。 这些数据提供了关于温度、不透明度、等离子体形成过程以及等离子体内部和周围环境气体中热流的见解。 恒定发射的轮廓表明，由足够密集气体形成的等离子体在具有几电子伏特温度的情况下会收缩而不是膨胀。 由相对低压气体如7atm氩气形成的等离子体可以以接近单位的发射率辐射。 将输运和不透明度建模为来自逆轫致辐射需要电离程度远高于根据Saha方程预期的值，即使通常修改以包括密度和屏蔽效应。 根据这个模型，电子和离子都与等离子体系数>1强烈耦合。 在形成后的最初几个纳秒内， 斯特藩-玻尔兹曼辐射和向周围气体的热传导太弱，无法解释观察到的冷却速率，这表明等离子体内部的输运主导其演化。 然而，等离子体本身的热传导也很小，正如热不均匀性的持续时间远长于时间尺度所表明的那样。 等离子体与周围环境隔离的事实使其成为通过所述系统和技术研究此类高密度等离子体的状态方程和流体力学的理想系统。 显示英文摘要

摘要： Compressed ultrafast photography (CUP) is applied to laser breakdown in argon and xenon under pressures up to 40atm to obtain 2D images of the plasma dynamics of single events with a spatial resolution of 250x100 pixels and an equivalent frame rate of 500 GHz. Light emission as a function of position and time is measured through red, green, blue, and broad-band filters. The spatially encoded and temporally sheared image normally used in CUP is now enhanced by the introduction of a constraint given by a spatially integrated and temporally sheared unencoded signal. The data yield insights into the temperature, opacity, the plasma formation process, and heat flow within the plasma and to the surrounding ambient gas. Contours of constant emission indicate that plasmas formed from sufficiently dense gas contract rather than expand despite having a temperature of a few eV. Plasmas formed from relatively low pressure gases such as 7atm argon can radiate with emissivity near unity. Modeling transport and opacity as arising from inverse Bremsstrahlung requires a degree of ionization that strongly exceeds expectations based on Saha's equation even as customarily modified to include density and screening. According to this model, both electrons and ions are strongly coupled with a plasma coefficient >1. During the first few nanoseconds after formation, Stefan-Boltzmann radiation and thermal conduction to ambient gas are too weak to explain the observed cooling rates, suggesting that transport within the plasma dominates its evolution. Yet, thermal conduction within the plasma itself is also small as indicated by the persistence of thermal inhomogeneities for far longer timescales. The fact that plasma is isolated from the surroundings makes it an excellent system for the study of the equation of state and hydrodynamics of such dense plasmas via the systems and techniques described.