A novel mechanism for injection, emittance selection, and postacceleration for laser wakefield electron acceleration is identified and described. It is shown that a laser prepulse can create an ionized plasma filament through multiphoton ionization and this heats the electrons and ions, driving an ellipsoidal blast-wave aligned with the laser-axis. The subsequent high-intensity laser-pulse generates a plasma wakefield which, on entering the leading edge of the blast-wave structure, encounters a sharp reduction in electron density, causing density down-ramp electron injection. The injected electrons are accelerated to $\sim 2\mathrm{MeV}$ within the blast-wave. After the main laser-pulse has propagated past the blast-wave, it drives a secondary wakefield within the homogenous background plasma. On exiting the blast-wave structure, the preaccelerated electrons encounter these secondary wakefields, are retrapped, and accelerated to higher energies. Due to the longitudinal extent of the blast-wave, only those electrons with small transverse velocity are retrapped, leading to the potential for the generation of electron bunches with reduced transverse size and emittance.

中文翻译：

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激光等离子加速器的预脉冲形气体靶中的电子俘获和再注入

确定并描述了一种新颖的注入，发射率选择和激光加速场电子加速后加速的机制。结果表明，激光预脉冲可以通过多光子电离产生离子化的等离子体灯丝，并加热电子和离子，从而驱动与激光轴对准的椭圆形爆炸波。随后的高强度激光脉冲产生等离子体唤醒场，该等离子体唤醒场在进入爆炸波结构的前沿时会遇到电子密度的急剧下降，从而导致密度下降的电子注入。注入的电子被加速到$〜2\mathrm{病毒}$在爆炸波中。主激光脉冲传播通过爆炸波后，它将在均匀的背景等离子体内驱动次级尾波场。在离开爆炸波结构时，预加速的电子遇到这些次级尾流场，被重新俘获，并被加速到更高的能量。由于爆炸波的纵向范围，只有那些具有较小横向速度的电子才被重新捕获，从而导致产生具有减小的横向尺寸和发射率的电子束的可能性。