Attospiral generation upon interaction of circularly polarized intense laser pulses with conelike targets

Highly efficient harmonic vortex generation from a laser irradiated hollow-cone target

It has been recently reported that ultraviolet harmonic vortices can be produced when a high-power circular-polarized laser pulse travels through a micro-scale waveguide. However, the harmonic generation quenches typically after a few tens of microns of propagation, due to the buildup of electrostatic potential that suppresses the amplitude of the surface wave. Here we propose to use a hollow-cone channel to overcome this obstacle. When traveling in a cone target, the laser intensity at the entrance is relatively low to avoid extracting too many electrons, while the slow focusing by the cone channel subsequently counters the established electrostatic potential, allowing the surface wave to maintain a high amplitude for a much longer distance. According to three-dimensional particle-in-cell simulations, the harmonic vortices can be produced with very high efficiency >20%. The proposed scheme paves the way for the development of powerful optical vortices sources in the extreme ultraviolet regime-an area of significant fundamental and applied physics potential.

Attosecond bunches of gamma photons and positrons generated in nanostructure targets

The subatomic experimental exploration of physical processes on extremely short time scales has become possible by the generation of high-quality electron bunches and x-ray pulses with subfemtosecond durations. Increasing the photon energy from the x-ray to gamma-ray regime makes probing of extremely small space-time domains accessible. Here, a mechanism for generating attosecond gamma photon and positron bunches with small divergence using laser intensities below 10^{23}W/cm^{2} is proposed. In contrast with previous works, in our scheme a single laser pulse is sufficient instead of two counterpropagating pulses. Numerical simulations are used to formulate the conditions for confined radiation and to characterize the generated photon and positron bunches.

GigaGauss solenoidal magnetic field inside bubbles excited in under-dense plasma

This paper proposes a novel and effective method for generating GigaGauss level, solenoidal quasi-static magnetic fields in under-dense plasma using screw-shaped high intensity laser pulses. This method produces large solenoidal fields that move with the driving laser pulse and are collinear with the accelerated electrons. This is in contrast with already known techniques which rely on interactions with over-dense or solid targets and generates radial or toroidal magnetic field localized at the stationary target. The solenoidal field is quasi-stationary in the reference frame of the laser pulse and can be used for guiding electron beams. It can also provide synchrotron radiation beam emittance cooling for laser-plasma accelerated electron and positron beams, opening up novel opportunities for designs of the light sources, free electron lasers, and high energy colliders based on laser plasma acceleration.

Energetic electron-bunch generation in a phase-locked longitudinal laser electric field

Energetic electron acceleration processes in a plasma hollow tube irradiated by an ultraintense laser pulse are investigated. It is found that the longitudinal component of the laser field is much enhanced when a linear polarized Gaussian laser pulse propagates through the plasma tube. This longitudinal field is of π/2 phase shift relative to the transverse electric field and has a π phase interval between its upper and lower parts. The electrons in the plasma tube are first pulled out by the transverse electric field and then trapped by the longitudinal electric field. The trapped electrons can further be accelerated to higher energy in the presence of the longitudinal electric field. This acceleration mechanism is clearly illustrated by both particle-in-cell simulations and single particle modelings.