Understanding the solid target dynamics resulting from the interaction with an ultrashort laser pulse is a challenging fundamental multi-physics problem involving atomic and solid-state physics, plasma physics, and laser physics. Knowledge of the initial interplay of the underlying processes is essential to many applications ranging from low-power laser regimes like laser-induced ablation to high-power laser regimes like laser-driven ion acceleration. Accessing the properties of the so-called pre-plasma formed as the laser pulse’s rising edge ionizes the target is complicated from the theoretical and experimental point of view, and many aspects of this laser-induced transition from solid to overdense plasma over picosecond timescales are still open questions. On the one hand, laser-driven ion acceleration requires precise control of the pre-plasma because the efficiency of the acceleration process crucially depends on the target properties at the arrival of the relativistic intensity peak of the pulse. On the other hand, efficient laser ablation requires, for example, preventing the so-called “plasma shielding”. By capturing the dynamics of the initial stage of the interaction, we report on a detailed visualization of the pre-plasma formation and evolution. Nanometer-thin diamond-like carbon foils are shown to transition from solid to plasma during the laser rising edge with intensities < 10¹⁶ W/cm². Single-shot near-infrared probe transmission measurements evidence sub-picosecond dynamics of an expanding plasma with densities above 10²³ cm⁻³ (about 100 times the critical plasma density). The complementarity of a solid-state interaction model and kinetic plasma description provides deep insight into the interplay of initial ionization, collisions, and expansion.

了解与超短激光脉冲相互作用所产生的固体目标动力学是一个具有挑战性的基本多物理问题，涉及原子和固体物理、等离子体物理和激光物理。了解基础过程的初始相互作用对于许多应用至关重要，从低功率激光状态（如激光诱导烧蚀）到高功率激光状态（如激光驱动离子加速）。从理论和实验的角度来看，获取当激光脉冲的上升沿电离目标时形成的所谓前等离子体的特性是复杂的，并且这种激光诱导的在皮秒时间尺度上从固体到高密度等离子体的转变的许多方面都存在问题。仍有待解决的问题。一方面，激光驱动离子加速需要对前等离子体进行精确控制，因为加速过程的效率关键取决于脉冲相对论强度峰值到达时的目标特性。另一方面，有效的激光烧蚀需要防止所谓的“等离子体屏蔽”。通过捕获相互作用初始阶段的动态，我们报告了前等离子体形成和演化的详细可视化。纳米薄类金刚石碳箔在强度 < 10 ¹⁶ W/cm²的激光上升沿期间从固体转变为等离子体。单次近红外探针传输测量证明了密度高于 10 ²³ cm ^-3（大约是临界等离子体密度的 100 倍）的膨胀等离子体的亚皮秒动力学。固态相互作用模型和动力学等离子体描述的互补性提供了对初始电离、碰撞和膨胀的相互作用的深入了解。