7th International Conference on Matter and Radiation at Extremes (ICMRE2024)

We present our investigations on the hot electrons generated from two-plasmon decay (TPD) instability driven by laser pulses with intensity modulated by a frequency ∆ω_m. Our primary focus lies on scenarios where ∆ω_m is on the same order of the TPD growth rate γ₀ (∆ω_m ~ γ₀), corresponding to moderate laser frequency bandwidths for TPD mitigation. With ∆ω_m conveniently modeled by a basic two-color scheme of the laser wave fields in fully-kinetic particle-in-cell simulations, we demonstrate that the energies of TPD modes and hot electrons exhibit intermittent evolution at the frequency ∆ω_m, particularly when ∆ω_m ~ γ₀. With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, f_hot, changes significantly with ∆ω_m. While f_hot drops notably with increasing ∆ω_m at large ∆ω_m limit as expected, it goes anomalously beyond the hot electron energy ratio for a single-frequency incident laser pulse with the same average intensity when ∆ω_m falls below a specific threshold frequency ∆ω_c. We find this threshold frequency primarily depends on γ₀ and the collisional damping rate of plasma waves, with relatively lower sensitivity to the density scale length. We develop a scaling model characterizing the relation of ∆ω_c and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios. Interestingly, the 3ω₀/2 scattering due to TPD can be lower for ∆ω_m that corresponds to enhanced f_hot, qualitatively agreeing with the recent experiments on Kunwu broadband laser facility .
 

inertial confinement fusion,Two-plasmon decay instability,broadband laser,intensity modulations,Hot electron