Electron Acceleration in Ionizing Gas by Self-Divergent Amplitude-Modulated Laser Pulses

We investigate electron acceleration driven by a self-diverging laser filament propagating through a tunnel-ionizing gas. When a high-intensity, amplitude-modulated laser interacts with the gas, it ionizes the medium and generates plasma. Due to local plasma density gradients, the laser filament diverges as it propagates, altering the dynamics of electron acceleration. Electrons can gain energy from the rising edge of the laser pulse, while the subsequent divergence of the laser helps mitigate deceleration by reducing the overlap between the trailing fields and the electron trajectory. Consequently, a significant portion of the acquired energy can be retained. To optimize the acceleration process, the spatial alignment between the laser pulse peak and the electron position is crucial. We develop a theoretical model to describe the divergence behavior of the laser filament and its impact on electron dynamics. Using this model, we estimate the achievable electron energy gain and derive scaling laws to guide the optimization and control of the acceleration process. This work suggests a novel mechanism for enhancing electron energy gain through the interaction of amplitude-modulated laser filaments with gas jets.