Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet, especially in dielectric targets. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the field ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than $5\times 10^{19}~\text{W}/\text{cm}^{2}$ that produce high relativistic electron current densities.

中文翻译：

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超强激光驱动的相对论电子在介电目标中的传输

超强激光驱动的相对论电子提供了一种将物质加热到与许多应用相关的高能量密度状态的方法。然而，相对论电子在固体靶中的传输尚未得到很好的理解，尤其是在介电靶中。我们通过包括场电离和碰撞电离过程，展示了硅靶中相对论电子传输的第一个详细的二维粒子细胞模拟。发现电离波在绝缘体中传播，其速度取决于激光强度并且比相对论电子速度慢。由于自由电子和离子的集体效应，在鞘场前观察到广泛分布的电场。电场比场电离的阈值电场弱得多。 $5\times 10^{19}~\text{W}/\text{cm}^{2}$ 产生高相对论电子电流密度。