We numerically investigate the impact of Coulomb collisions on the ion dynamics in high-$Z$, solid density caesium hydride and copper targets, irradiated by high-intensity ($I\approx2{-}5\times10^{20}{\rm\,Wcm^{-2}}$), ultrashort (${\sim}10{\rm\,fs}$), circularly polarized laser pulses, using particle-in-cell simulations. Collisions significantly enhance electron heating, thereby strongly increasing the speed of a shock wave launched in the laser-plasma interaction. In the caesium hydride target, collisions between the two ion species heat the protons to ${\sim}100{-}1000{\rm\,eV}$ temperatures, however, in contrast to previous work [A.E.~Turrell et~al., 2015~\emph{Nat.~Commun.}~{\bf 6}~8905], this process happens in the upstream only, due to a nearly total proton reflection. In the case of a copper target, the ion reflection can start as a self-amplifying process, bootstrapping itself. Afterwards, collisions between the reflected and upstream ions heat these two populations significantly. When increasing the pulse duration to $60{\rm\,fs}$, the shock front more clearly decouples from the laser piston, and so can be studied without direct interference from the laser. The shock wave formed at early times exhibits properties typical of both hydrodynamic and electrostatic shocks, including ion reflection. At late times, the shock is seen to evolve into a hydrodynamic blast wave.

中文翻译：

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超强短脉冲激光驱动的薄箔目标静电冲击动力学的碰撞效应

我们数值研究了库仑碰撞对高强度 ($I\approx2{-}5\times10^{20}{\rm \,Wcm^{-2}}$)、超短 (${\sim}10{\rm\,fs}$)、圆偏振激光脉冲，使用细胞内粒子模拟。碰撞显着增强了电子加热，从而大大增加了激光-等离子体相互作用中发射的冲击波的速度。在氢化铯靶中，两种离子物质之间的碰撞将质子加热到 ${\sim}100{-}1000{\rm\,eV}$ 温度，然而，与之前的工作相反 [AE~Turrell et~al ., 2015~\emph{Nat.~Commun.}~{\bf 6}~8905]，由于几乎全质子反射，这个过程只发生在上游。在铜靶的情况下，离子反射可以作为一个自我放大过程开始，自我引导。之后，反射离子和上游离子之间的碰撞显着加热这两个群体。当脉冲持续时间增加到 $60{\rm\,fs}$ 时，激波前沿更清楚地与激光活塞分离，因此可以在没有激光直接干扰的情况下进行研究。早期形成的冲击波表现出流体动力冲击和静电冲击的典型特性，包括离子反射。在后期，可以看到冲击演变成流体动力冲击波。因此可以在没有激光直接干扰的情况下进行研究。早期形成的冲击波表现出流体动力冲击和静电冲击的典型特性，包括离子反射。在后期，可以看到冲击演变成流体动力冲击波。因此可以在没有激光直接干扰的情况下进行研究。早期形成的冲击波表现出流体动力冲击和静电冲击的典型特性，包括离子反射。在后期，可以看到冲击演变成流体动力冲击波。