Second-Harmonic Generation Through Backward Raman Scattering in Magnetized Plasmas Driven by Circularly Polarized Intense Lasers

The nonlinear dynamics of backward Raman scattering (BRS) in a magnetized plasma channel driven by an intense circularly polarized laser pulse are investigated through a combined analytical and numerical approach, with emphasis on the emergence and controllability of a secondary spectral peak. The analysis is performed in the relativistic laser–plasma interaction regime under experimentally relevant plasma densities and axial magnetic-field strengths. A fluid-based theoretical framework is developed to describe the nonlinear cascade linking primary BRS-driven plasma wave amplification, oscillating two-stream instability (OTSI), nonlinear current generation within a self-formed ponderomotive channel, and radiation of the secondary electromagnetic mode. Systematic parameter studies reveal a strong sensitivity of the entire cascade to the relative handedness of laser polarization and axial magnetic field direction, as well as to cyclotron resonance strength. Resonant right-handed circular polarization significantly enhances ponderomotive expulsion, channel depth, BRS and OTSI growth rates, nonlinear current density, and the amplitude of the secondary harmonic, whereas non-resonant left-handed polarization effectively suppresses these processes. Fully kinetic particle-in-cell simulations using EPOCH, together with macroscopic finite-element modelling in COMSOL Multiphysics, corroborate the polarization- and magnetization-dependent wake modulation and channelling efficiency across a wide range of laser wavelengths, pulse durations, and plasma densities. The temporal evolution and saturation of OTSI, resilience to density inhomogeneities, and wavenumber-resolved resonance tuning illustrate axial magnetization as a flexible control mechanism for adjusting the intensity, spectral position, bandwidth, and stability of multi-peak Raman spectra. These findings demonstrate that cyclotron resonance and polarization control are effective methods for manipulating nonlinear Raman emission in high-intensity laser–magnetized plasma interactions, offering predictive insights for forthcoming kinetic simulations and experimental implementations. PACS: 52.38.-r, 52.35.Mw, 52.65.Rr