A theoretical model of high-harmonic generation from two-color relativistic circularly polarized laser pulse interacting with over-dense plasmas

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.