Anomalous hot electron generation from two-plasmon decay instability driven by broadband laser pulses with intensity modulations

We investigate the hot electrons generated from two-plasmon decay (TPD) instability driven by laser pulses with intensity modulated by a frequency Δ ω m using theoretical and numerical approaches. Our primary focus lies on scenarios where Δ ω m is on the same order of the TPD growth rate γ 0 ( Δ ω m ∼ γ 0 ), corresponding to moderate laser frequency bandwidths for TPD mitigation. With Δ 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 Δ ω m , particularly when Δ ω m ∼ γ 0 . With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, f hot , changes significantly with Δ ω m . While f hot drops notably with increasing Δ ω m at large Δ 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 Δ ω m falls below a specific threshold frequency Δ ω c . This anomaly arises from the pronounced sensitivity of f hot to variations in laser intensity. We find this threshold frequency Δ ω c primarily depends on γ 0 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 Δ ω c and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios.