Terahertz-driven positron acceleration assisted by ultra-intense lasers.

Generation and acceleration of energetic positrons based on laser plasma have attracted intense attention due to their potential applications in medical physics, high energy physics, astrophysics and nuclear physics. However, such compact positron sources face a series of challenges including the beam dispersion, dephasing and unstability. Here, we propose a scheme that couples the all-optical generation of electron-positron pairs and rapid acceleration of copious positrons in the terahertz (THz) field.

Ultra-brilliant GeV betatronlike radiation from energetic electrons oscillating in frequency-downshifted laser pulses.

Electrons can be accelerated to GeV energies with high collimation via laser wakefield acceleration in the bubble regime and emit bright betatron radiation in a table-top size. However, the radiation brightness is usually limited to the third-generation synchrotron radiation facilities operating at similar photon energies. Using a two-stage plasma configuration, we propose a novel scheme for generating betatronlike radiation with an extremely high brilliance.

Tunable elliptically polarized Hermite-Gaussian terahertz radiation driven by two-color twisted laser pulses.

We propose a scheme for tunable elliptically polarized terahertz (THz) radiation by two-color linearly polarized Laguerre-Gaussian lasers irradiating gas plasmas. Three-dimensional particle-in-cell simulations show that the field strength of THz radiation can achieve MV/cm-scale, and the radiation frequency is determined by the plasma frequency and the electron cyclotron frequency. The emitted THz radiation is Hermite-Gaussian (HG) with a broadband waveform which can be attributed to the axial magnetic fields induced by the twisted drive pulses.

Extremely brilliant GeV γ-rays from a two-stage laser-plasma accelerator.

Recent developments in laser-wakefield accelerators have led to compact ultrashort X/γ-ray sources that can deliver peak brilliance comparable with conventional synchrotron sources. Such sources normally have low efficiencies and are limited to 10 photons/shot in the keV to MeV range. We present a novel scheme to efficiently produce collimated ultrabright γ-ray beams with photon energies tunable up to GeV by focusing a multi-petawatt laser pulse into a two-stage wakefield accelerator.

Copious positron production by femto-second laser via absorption enhancement in a microstructured surface target.

Laser-driven positron production is expected to provide a non-radioactive, controllable, radiation tunable positron source in laboratories. We propose a novel approach of positron production by using a femto-second laser irradiating a microstructured surface target combined with a high-Z converter. By numerical simulations, it is shown that both the temperature and the maximum kinetic energy of electrons can be greatly enhanced by using a microstructured surface target instead of a planar target.

Dense relativistic electron mirrors from a Laguerre-Gaussian laser-irradiated micro-droplet.

We investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly polarized Laguerre-Gaussian lasers. The surface electrons are expelled from the droplet by the laser's radial electric field and evolve into dense sheets after leaving the droplet. These electrons are trapped in the potential well of the laser's transverse ponderomotive force and are steadily accelerated to about 100 MeV by the longitudinal electric field.

Attosecond electron bunches from a nanofiber driven by Laguerre-Gaussian laser pulses.

Generation of attosecond bunches of energetic electrons offers significant potential from ultrafast physics to novel radiation sources. However, it is still a great challenge to stably produce such electron beams with lasers, since the typical subfemtosecond electron bunches from laser-plasma interactions either carry low beam charge, or propagate for only several tens of femtoseconds. Here we propose an all-optical scheme for generating dense attosecond electron bunches via the interaction of an intense Laguerre-Gaussian (LG) laser pulse with a nanofiber.

Ultra-bright γ-ray emission and dense positron production from two laser-driven colliding foils.

Matter can be transferred into energy and the opposite transformation is also possible by use of high-power lasers. A laser pulse in plasma can convert its energy into γ-rays and then e e pairs via the multi-photon Breit-Wheeler process. Production of dense positrons at GeV energies is very challenging since extremely high laser intensity ~10 Wcm is required.

Ultra-bright γ-ray flashes and dense attosecond positron bunches from two counter-propagating laser pulses irradiating a micro-wire target.

We propose a novel scheme to generate ultra-bright ultra-short γ-ray flashes and high-energy-density attosecond positron bunches by using multi-dimensional particle-in-cell simulations with quantum electrodynamics effects incorporated. By irradiating a 10 PW laser pulse with an intensity of 10 W/cm onto a micro-wire target, surface electrons are dragged-out of the micro-wire and are effectively accelerated to several GeV energies by the laser ponderomotive force, forming relativistic attosecond electron bunches. When these electrons interact with the probe pulse from the other side, ultra-short γ-ray flashes are emitted with an ultra-high peak brightness of 1.

All-optical bright γ-ray and dense positron source by laser driven plasmas-filled cone.

An all-optical scheme for bright γ-rays and dense ee pair source is proposed by irradiating a 10 W/cm laser onto a near-critical-density plasmas filled Al cone. Two-dimensional (2D) QED particle-in-cell (PIC) simulations show that, a dense electron bunch is confined in the laser field due to the radiation reaction and the trapped electrons oscillate transversely, emitting bright γ-rays forward in two ways: (1) nonlinear Compton scattering due to oscillation of electrons in the laser field, and (2) Compton backwardscattering resulting from the bunch colliding with the reflected laser by the cone tip. Finally, the multi-photon Breit-Wheeler process is initiated, producing abundant ee pairs with a density of ∼ 10m.

Bright betatronlike x rays from radiation pressure acceleration of a mass-limited foil target.

By using multidimensional particle-in-cell simulations, we study the electromagnetic emission from radiation pressure acceleration of ultrathin mass-limited foils. When a circularly polarized laser pulse irradiates the foil, the laser radiation pressure pushes the foil forward as a whole. The outer wings of the pulse continue to propagate and act as a natural undulator.

Stable laser-driven proton beam acceleration from a two-ion-species ultrathin foil.

By using multidimensional particle-in-cell simulations, we present a new regime of stable proton beam acceleration which takes place when a two-ion-species shaped foil is illuminated by a circularly polarized laser pulse. In the simulations, the lighter protons are nearly instantaneously separated from the heavier carbon ions due to the charge-to-mass ratio difference. The heavy ion layer expands in space and acts to buffer the proton layer from the Rayleigh-Taylor-like (RT) instability that would have otherwise degraded the proton beam acceleration.