Enhancement of high-order harmonic generation based on Landau damping in laser interactions with plasma

High-order harmonic generation (HHG) plays a key role in producing coherent extreme ultraviolet (EUV) and x-ray radiation, which is crucial for applications in attosecond science and high-energy density physics. The intensity and order of high-order harmonics are crucial for advancing their applications. In this paper, a scheme is proposed to generate harmonics by the relativistic oscillating mirror (ROM) based on the energy exchange between electron and excited plasma wave by Landau damping, which employs dual laser pulses to sequentially excite the plasma surface electron oscillation to enhance the intensity and order of harmonics. Through theory and numerical analysis, we discover that our scheme significantly enhances the intensity of higher-order harmonics by an order of magnitude compared to typical harmonic generation methods of the same energy, and observe the higher-order harmonics. Furthermore, we investigate the essential factors affecting energy exchange in Landau damping and find that there exists an optimal pulse interval and energy ratio to maximize the energy exchange. The scheme based on Landau damping for generating high-order harmonics offers an alternative perspective for advancing HHG research and applications.