环境空气中的等离子体加速在紧密聚焦的超短红外激光束中
Ambient air plasma acceleration in tightly-focused ultrashort infrared laser beams
AI总结：
研究通过PIC模拟探讨了在环境空气中紧密聚焦超短红外激光束中利用相对论性ponderomotive力加速电子的机制，并验证了在2.5μm波长时电子动能可达1.6MeV。
摘要：
最近的实验和理论结果已经证明了通过在环境空气中紧密聚焦几个周期的激光束可以将电子加速到MeV范围的可能性。利用粒子-细胞（PIC）模拟，这种配置在更精确的建模方法下被重新审视，以分析和优化导致电子加速的机制。特别是，推导出一个线性极化的紧密聚焦超短激光场的解析模型，并将其与PIC代码耦合，使我们能够建模由高数值孔径镜面反射的激光束与激光诱导等离子体的相互作用。进行了一系列3D PIC模拟，其中激光波长从800nm变化到7.0μm，而电场的归一化振幅从a0=3.6变化到a0=7.0。电子的优先向前加速，以及等离子体中激光强度演变的分析和电子数密度的数据，证实了相对论性 ponderomotive 力是加速的原因。我们还证明，当中心波长为2.5μm时，电子的动能达到最大值约为1.6MeV。
英文摘要：
Recent experimental and theoretical results have demonstrated the possibility of accelerating electrons in the MeV range by focusing tightly a few-cycle laser beam in ambient air. Using Particle-In-Cell (PIC) simulations, this configuration is revisited within a more accurate modelling approach to analyze and optimize the mechanism responsible for electron acceleration. In particular, an analytical model for a linearly polarized tightly-focused ultrashort laser field is derived and coupled to a PIC code, allowing us to model the interaction of laser beams reflected by high-numerical aperture mirrors with laser-induced plasmas. A set of 3D PIC simulations is performed where the laser wavelength is varied from 800 nm to 7.0 $μ$m while the normalized amplitude of the electric field is varied from $a_{0} = 3.6$ to $a_{0} = 7.0$. The preferential forward acceleration of electrons, as well as the analysis of the laser intensity evolution in the plasma and data on electron number density, confirm that the relativistic ponderomotive force is responsible for the acceleration. We also demonstrate that the electron kinetic energy reaches a maximum of $\approx1.6$ MeV when the central wavelength is of 2.5 $μ$m.
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