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 Δωm using theoretical and numerical approaches. Our primary focus lies on scenarios where Δωm is on the same order of the TPD growth rate γ0 ( ), corresponding to moderate laser frequency bandwidths for TPD mitigation. With Δωm 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 Δωm, particularly when . With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, , changes significantly with Δωm. While drops notably with increasing Δωm at large Δωm 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 Δωm falls below a specific threshold frequency Δωc. This anomaly arises from the pronounced sensitivity of to variations in laser intensity. We find this threshold frequency Δωc 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 Δωc and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios.