Moving electron vortices have been observed in laser interaction with non-uniform near-critical-density plasma by multi-dimensional Particle-in-Cell simulations. In two dimensional geometry there are two vortices with opposite magnetic polarity, moving perpendicularly to the plasma density gradient direction. The field distribution and particle motion composing such moving structure have been clearly observed in simulations, which explains the vortex motion. Two components of loop currents are formed around each electron vortex, which dominate the vortex motion. The moving velocity can be as large as 0.2c level, forming relativistic vortices inside the plasma. Laser plasma conditions such as intensity, polarization, density profile and external magnetic field effects on the vortex motion and evolution are also studied. In three dimensions, the structure appears as an expanding magnetic ring with an internal magnetic field up to 1000 Tesla. Such vortex structures suggest an interesting way of energy (with more than 5% of the laser energy) transportation to ambient plasmas as far as 50µm away from the laser-plasma interaction region, which may have applications in laser plasma based inertial confinement fusion and laboratory astrophysics.

Structure and transportation of electron vortices in near-critical density plasmas driven by ultrashort intense laser pulses have been studied by multi-dimensional particle-in-cell simulations. Dimensional features of electron vortices are revealed. In two-dimensional geometry, two electron vortices and a quasi-static magnetic dipole are closely coupled. In three-dimensional geometry, a moving electron vortex ring associated with a closed magnetic ring moves in near-critical density plasmas. Such structure can transport some energy to the region where the laser pulse cannot reach. It is found that the motion of plasma ions makes the vortex magnetic energy dissipate quickly. These studies provide possible connection of electron vortices in nature with laser plasma experiments.

The influence of second-order dispersion (SOD) on stimulated Raman scattering (SRS) in the interaction of ultrashort intense laser with plasma was investigated. More significant backward SRS was observed with the increase of the absolute value of SOD (|ψ2|). The integrated intensity of the scattered light is positively correlated to the driver laser pulse duration. Accompanied by the side SRS, filaments with different angles along the laser propagation direction were observed in the transverse shadowgraph. A model incorporating Landau damping and above-threshold ionization was developed to explain the SOD-dependent angular distribution of the filaments.

The origin of [Formula: see text] ions in picosecond intense laser–gas interaction was experimentally and numerically investigated. A nanosecond laser pulse was used to modulate the plasma condition, which helps to distinguish the origin of the helium ions with different charge states. By comparing the energy spectra of [Formula: see text] and [Formula: see text] ions in the experiments with/without plasma shaping, we found neither ion–atom nor electron–ion recombination is responsible for the [Formula: see text] generation, which is supported by two-dimensional hydrodynamic simulations and theoretical calculations.

Generation of nonlinear structures, such as stimulated Raman side scattering waves, post-solitons and electron vortices, during ultra-short intense laser pulse transportation in near-critical-density (NCD) plasmas are studied by using multi-dimensional particle-in-cell (PIC) simulations. In two-dimensional geometries, both P- and S- polarized laser pulses are used to drive these nonlinear structures and to check the polarization effects on them. In the S-polarized case, the scattered waves can be captured by surrounding plasmas leading to the generation of post-solitons, while the main pulse excites convective electric currents leading to the formation of electron vortices through Kelvin-Helmholtz instability (KHI). In the P-polarized case, the scattered waves dissipate their energy by heating surrounding plasmas. Electron vortices are excited due to the hosing instability of the drive laser. These polarization dependent physical processes are reproduced in two different planes perpendicular to the laser propagation direction in three-dimensional simulation with linearly polarized laser driver. The current work provides inspiration for future experiments of laser-NCD plasma interactions.