Tailliez C, Davoine X, Debayle A, Gremillet L, Bergé L
CEA, DAM, DIF, F-91297 Arpajon, France and Université Paris-Saclay, CEA, LMCE, 91680 Bruyères-le-Châtel, France.
Phys Rev Lett. 2022 Apr 29;128(17):174802. doi: 10.1103/PhysRevLett.128.174802.
Relativistic interactions between ultraintense (>10^{18} W cm^{-2}) laser pulses and magnetized underdense plasmas are known to produce few-cycle Cerenkov wake radiation in the terahertz (THz) domain. Using multidimensional particle-in-cell simulations, we demonstrate the possibility of generating high-field (>100 GV m^{-1}) THz bursts from helium gas plasmas embedded in strong (>100 T) magnetic fields perpendicular to the laser path. We show that two criteria must be satisfied for efficient THz generation. First, the plasma density should be adjusted to the laser pulse duration for a strong resonant excitation of the electromagnetic plasma wake. Second, in order to mitigate the damping of the transverse wake component across the density gradients at the plasma exit, the ratio of the relativistic electron cyclotron and plasma frequencies must be chosen slightly above unity, but not too large, lest the wake be degraded. Such conditions lead the outgoing THz wave to surpass in amplitude the electrostatic wakefield induced in a similar, yet unmagnetized plasma.
已知超强（>10^{18} W cm^{-2}）激光脉冲与磁化欠稠密等离子体之间的相对论相互作用会在太赫兹（THz）波段产生少周期切伦科夫尾波辐射。通过多维粒子模拟，我们证明了在垂直于激光路径的强（>100 T）磁场中嵌入的氦气等离子体产生高场（>100 GV m^{-1}）太赫兹脉冲串的可能性。我们表明，高效产生太赫兹需要满足两个条件。首先，应将等离子体密度调整到与激光脉冲持续时间匹配，以便对电磁等离子体尾波进行强共振激发。其次，为了减轻等离子体出口处密度梯度对横向尾波分量的阻尼，相对论电子回旋频率与等离子体频率之比必须选择略高于1，但不能太大，以免尾波退化。这些条件使得出射的太赫兹波在幅度上超过在类似但未磁化的等离子体中感应出的静电尾波场。
