paper

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

arXiv:2311.14956

Abstract

We investigate the hot electrons generated from two-plasmon decay (TPD) instability driven by laser pulses with intensity modulated by a frequency $I^ I ¨ _{m}$ . Our primary focus lies on scenarios where $I^ I ¨ _{m}$ is on the same order of the TPD growth rate $I^_{0}^{3}$ ( $I^ I ¨ _{m} \sim I^_{0}^{3}$ ), corresponding to moderate laser frequency bandwidths for TPD mitigation. With $I^ I ¨ _{m}$ 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 $I^ I ¨ _{m}$ , particularly when $I^ I ¨ _{m} \sim I^_{0}^{3}$ . With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, $f_{h o t}$ , changes significantly with $I^ I ¨ _{m}$ . While $f_{h o t}$ drops notably with increasing $I^ I ¨ _{m}$ at large $I^ I ¨ _{m}$ 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 $I^ I ¨ _{m}$ falls below a specific threshold frequency $I^ I ¨ _{c}$ . We find this threshold frequency primarily depends on $I^_{0}^{3}$ 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 $I^ I ¨ _{c}$ and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios.