Understanding the behaviour of matter under conditions of extreme temperature, pressure, density and electromagnetic fields has profound effects on our understanding of cosmologic objects and the formation of the universe. Lacking direct access to such objects, our interpretation of observed data mainly relies on theoretical models. However, such models, which need to encompass nuclear physics, atomic physics and plasma physics over a huge dynamic range in the dimensions of energy and time, can only provide reliable information if we can benchmark them to experiments under well-defined laboratory conditions. Due to the plethora of effects occurring in this kind of highly excited matter, characterizing isolated dynamics or obtaining direct insight remains challenging. High-density plasmas are turbulent and opaque for radiation below the plasma frequency and allow only near-surface insight into ionization processes with visible wavelengths. Here, the output of a high-harmonic seeded laser-plasma amplifier using eight-fold ionized krypton as the gain medium operating at a 32.8 nm wavelength is ptychographically imaged. A complex-valued wavefront is observed in the extreme ultraviolet (XUV) beam with high resolution. Ab initio spatio-temporal Maxwell–Bloch simulations show excellent agreement with the experimental observations, revealing overionization of krypton in the plasma channel due to nonlinear laser-plasma interactions, successfully validating this four-dimensional multiscale model. This constitutes the first experimental observation of the laser ion abundance reshaping a laser-plasma amplifier. The presented approach shows the possibility of directly modelling light-plasma interactions in extreme conditions, such as those present during the early times of the universe, with direct experimental verification.

了解物质在极端温度，压力，密度和电磁场条件下的行为，会对我们对宇宙学物体和宇宙形成的理解产生深远影响。由于无法直接访问此类对象，因此我们对观测数据的解释主要依赖于理论模型。但是，这样的模型需要在能量和时间的巨大动态范围内涵盖核物理学，原子物理学和等离子物理学，如果我们能够在明确定义的实验室条件下对它们进行基准测试，则它们只能提供可靠的信息。由于在这种高度激发的物质中会发生多种效应，因此表征孤立的动力学或获得直接的洞察力仍然具有挑战性。高密度等离子体对于低于等离子体频率的辐射来说是湍流且不透明的，并且仅允许近表面洞察可见波长的电离过程。在此，对使用八倍离子化k作为在32.8 nm波长下工作的增益介质的高谐波种子激光等离子体放大器的输出进行了谱图成像。在高分辨率的极紫外（XUV）光束中观察到复数值波前。从头开始的时空Maxwell-Bloch模拟显示与实验观察结果非常吻合，揭示了由于非线性激光-等离子体相互作用，等离子体通道中的over过度离子化，成功验证了此多维多尺度模型。这是重塑激光等离子体放大器的激光离子丰度的首次实验观察。