Investigation of early-time dynamics of laser-produced carbon plasma by collective Thomson scattering

激光产生的等离子体（LPP）已经研究了50多年，因为它与几个突出的科学和工业应用相关，例如惯性控制聚变和半导体制造的极紫外光刻（EUVL）。因此，了解激光辐照下LPP的特性具有重要的研究意义。然而，在激光照射（< 50ns）期间和之后不久，LPP动力学的实验研究从未进行过。主要原因是LPP高度不均匀，在空间（在几十微米内）和时间（在纳秒内）变化迅速，使得早期的LPP动力学不清楚。我们首次证明了利用集体汤姆逊散射方法（CTS）进行此类研究是可能的。它提供了在激光峰值后0 ~ 14 ns的时间延迟下，碳LPPs在二维空间中具有高度空间和时间分辨的等离子体参数（电子密度、电子温度和速度场）。此外，我们在与实验相同的条件下进行了二维辐射流体动力学模拟。因此，该结果允许对现有理论模型和仿真代码进行首次测试。我们发现一维等温模型比公认的绝热模型更能描述LPP在这一早期阶段的膨胀。

Laser-produced plasma (LPP) has been studied for over 50 years due to its relevance to several prominent scientific and industrial applications, such as inertial controlled fusion and extreme ultraviolet lithography (EUVL) for semiconductor manufacturing. Therefore, understanding the LPP characteristics during the laser irradiance is of great research interest. However, experimental studies on LPP dynamics during and soon after (< 50ns) the laser irradiance have never been performed. The major reason for this is that LPP is highly non-uniform and changes rapidly in both space (within tens of micrometers) and time (within nanoseconds), making the early LPP dynamics unclear.For the first time, we have demonstrated that such investigations are possible by utilizing the collective Thomson scattering method (CTS). It provides highly spatial and temporal resolved plasma parameters (electron density, electron temperature, and velocity field) of carbon LPPs in a 2-dimensional space, at the time delay of 0 to 14 ns after the laser peak. Additionally, we performed a 2D radiation hydrodynamic simulation under identical conditions as those used in the experiments. Therefore, the results allow for a first test of existing theoretical models and simulation codes. We found that the 1-dimensional isothermal model could better describe the LPP expansion at this early stage, rather than the well-accepted adiabatic model.