In this article, we set up a theoretical model to investigate the physical mechanism of circularly polarized (CP) high-harmonic generation (HHG) by two-color relativistic driving lasers (with one at fundamental and the other at second harmonic). The compression effect of the electron density profile and the boundary oscillating are responsible for the harmonic emission. Based on this model, the scaling law between the intensity of the 4th harmonic and that of the fundamental driving laser can be successfully acquired. Our theoretical model holds only when the second-harmonic laser is much weaker than the fundamental laser. For more general cases, particle-in-cell (PIC) simulations are performed to demonstrate that the HHG efficiency. The intensity of higher order harmonics can be effectively tuned by gradually enhancing the intensity of the second-harmonic driving laser.

中文翻译：

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双色相对论圆偏振激光脉冲与高密度等离子体相互作用产生高次谐波的理论模型

在本文中，我们建立了一个理论模型来研究双色相对论驱动激光器（一个在基波，另一个在二次谐波）产生圆偏振（CP）高次谐波（HHG）的物理机制。电子密度分布的压缩效应和边界振荡是造成谐波发射的原因。基于该模型，可以成功获得4次谐波强度与基波驱动激光强度之间的标度律。我们的理论模型仅在二次谐波激光比基本激光弱得多时才成立。对于更一般的情况，执行细胞内粒子 (PIC) 模拟以证明 HHG 效率。