Structured laser--plasma interactions at ultra-high intensities

Abstract

Light can carry and transfer a well-defined orbital angular momentum (OAM) [1] along the propagation axis and is often called twisted light. This quality opens new research in highly non-linear (I 1022 W/cm2) laser-plasma interactions, including magnetic field generation [2], electron/positron acceleration in laser-plasma accelerators [3], high orbital angular momentum harmonic generation [4], and direct laser acceleration of ions [5]. However, the full potential of twisted light interacting with plasma is yet unexplored.

We studied three novel scenarios analytically and through three-dimensional particle-in-cell simulations using OSIRIS [6]; enhanced proton acceleration, the light properties in the cutoff region of plasma, and wakefield acceleration through light with self-torque.

The main project focused on proton acceleration. By exploiting the benefits of a high-intensity twisted light pulse impinging a double-layer target, we could reduce the accelerated proton bunch divergence by almost an order of magnitude while maintaining its energy compared to the conventional Gaussian method [7]. Here, we identified that relativistic self-focusing in the near-critical plasma layer of the target and the light's OAM contents play a crucial role in improved proton acceleration.

We also explored light springs and light with self-torque by combining twisted light modes. First, a study of the properties of a light spring in the cutoff region of plasma has shown a similar characteristic behavior as a compressed mechanical spring [8]. Second, we identified that a wakefield configuration with self-torque in the non-linear regime leads to azimuthal forces and the formation of quasi-helical electron beams [9].

Twisted light is still an open field in laser-plasma research and has the potential to lead to new regimes of particle acceleration, radiation processes, and eventually laser fusion research.