Lin J, Ma Y, Schwartz R, Woodbury D, Nees J A, Mathis M, Thomas A G R, Krushelnick K, Milchberg H
Opt Express. 2019 Apr 15;27(8):10912-10923. doi: 10.1364/OE.27.010912.
There has been growing interest both in studying high intensity ultrafast laser plasma interactions with adaptive control systems as well as using long wavelength driver beams. We demonstrate the coherent control of the dynamics of laser-wakefield acceleration driven by ultrashort (∼ 100 fs) mid-infrared (∼ 3.9 μm) laser pulses. The critical density at this wavelength is 7.3 × 10 cm, which is achievable with an ordinary gas target system. Interactions between mid-infrared laser pulses and such near-critical-density plasma may be beneficial due to much higher absorption of laser energy. In addition, the normalized vector potential of the laser field a increases with longer laser wavelength, lowering the required peak laser intensity to drive non-linear laser-wakefield acceleration. Here, MeV level, collimated electron beams with non-thermal, peaked energy spectra are generated. Optimization of electron beam qualities are realized through adaptive control of the laser wavefront. A genetic algorithm controlling a deformable mirror improves the electron total charge, energy spectra, beam pointing and stability at various plasma density profiles. Particle-in-cell simulations reveal that the optimal wavefront causes an earlier injection on the density up-ramp and thus higher energy gain as well as less filamentation during the interaction, which leads to the improvement in electron beam collimation and energy spectra.
研究高强度超快激光与自适应控制系统的等离子体相互作用以及使用长波长驱动光束的兴趣与日俱增。我们展示了由超短（约100飞秒）中红外（约3.9微米）激光脉冲驱动的激光尾场加速动力学的相干控制。该波长下的临界密度为7.3×10厘米，这可以通过普通气体靶系统实现。由于激光能量的更高吸收，中红外激光脉冲与这种近临界密度等离子体之间的相互作用可能是有益的。此外，激光场的归一化矢量势a随着激光波长的增加而增加，降低了驱动非线性激光尾场加速所需的峰值激光强度。在此，产生了具有非热、尖峰能谱的兆电子伏特级准直电子束。通过对激光波前的自适应控制实现了电子束质量的优化。一种控制可变形镜的遗传算法改善了各种等离子体密度分布下的电子总电荷、能谱、束指向和稳定性。粒子模拟表明，最佳波前会在密度上升斜坡上更早注入，从而在相互作用期间获得更高的能量增益以及更少的丝状化，这导致电子束准直和能谱得到改善。
