The effects of laser polarization and wavelength on injection dynamics of a laser wakefield accelerator
The effects of laser polarization and wavelength on injection dynamics of a laser wakefield accelerator
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DOI：
10.1063/5.0051125
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发表时间：
2021-06
影响因子：
2.2
通讯作者：
Yong Ma;D. Seipt;A. Hussein;S. Hakimi;N. Beier;S. Hansen;J. Hinojosa;A. Maksimchuk;J. Nees;K. Krushelnick;A. Thomas;F. Dollar
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作者：
Yong Ma;D. Seipt;A. Hussein;S. Hakimi;N. Beier;S. Hansen;J. Hinojosa;A. Maksimchuk;J. Nees;K. Krushelnick;A. Thomas;F. Dollar
本文研究了激光偏振和波长对激光韦克菲尔德加速器中电子注入动力学的影响。在电离过程中，电子通过阈值以上电离获得剩余动量和动能，这与激光偏振有很强的依赖性。与线偏振激光脉冲相比，圆偏振激光脉冲使电离电子获得更高的剩余动量和动能增益。由于粒子捕获对初始条件的敏感性，这种剩余动量导致粒子注入，并在实验和粒子模拟中增强了总注入束电荷。由于阈值以上电离与激光波长的强相关性，在这项工作中，我们使用粒子模拟将研究扩展到长波长（高达20 μm）的驱动脉冲。由于动能的增益，可以预期，对于圆偏振，捕获的电荷将随着激光波长的增加而一致地增加，但这没有观察到。相反，在线性和圆偏振情况之间的相对捕获电荷中存在波长振荡，这是由于等离子体上的电离和加热效应而产生的。我们的研究突出了几种不同的物理效应之间的复杂的相互作用，包括注入制度高于阈值电离辅助注入，载波包络相位效应和电离注入电离梯度诱导的激光脉冲演化的破波注入，和热修改的尾流结构时，需要考虑外推激光韦克菲尔德场加速到不同的波长制度。
Here, we investigate the effects of laser polarization and wavelength on electron injection dynamics in a laser wakefield accelerator. During the ionization process, electrons gain residual momentum and kinetic energy via above threshold ionization, which has a strong dependence on laser polarization. A circularly polarized laser pulse results in a much higher residual momentum and kinetic energy gain for the ionized electrons compared with the linearly polarized case. This residual momentum results in particle injection because of the sensitivity of particle trapping to the initial conditions and enhanced the total injected beam charge in both experiments and particle-in-cell simulations. Due to the strong correlation of above threshold ionization with laser wavelength, in this work we extended the investigation to long wavelength (up to 20 μm) drive pulses using particle-in-cell simulations. Owing to the gain in kinetic energy, it may be expected that the charge trapped would consistently increase for circular polarization with increasing laser wavelength, but this was not observed. Instead, there are oscillations with wavelength in the relative trapped charge between linear and circular polarization cases, which arise because of ionization and heating effects on the plasma. Our studies highlight the complex interplay between several different physical effects, including injection regimes—above threshold ionization assisted injection, wave-breaking injection by carrier-envelope-phase effects and ionization injection—ionization gradient induced laser pulse evolution, and thermal modifications to the wake structure that need considering when extrapolating laser wakefield acceleration to different wavelength regimes.