Proton acceleration in a near-critical-density gas driven by a light spring (LS) pulse with a helical structure in its intensity profile is investigated using three-dimensional particle-in-cell simulations. Compared with other pulse modes with the same laser power, such as the Gaussian pulse or the donut Laguerre–Gaussian (LG) pulse, the LS structure significantly enhances the peak intensity and drives a stronger longitudinal acceleration field and transverse focusing field. Both the high intensity and helical structure of the LS pulse contribute to the formation of a bubble-like structure with a fine electron column on the axis, which is critical for stable proton acceleration. Therefore, it is very promising to obtain ultra-high-energy protons using LS pulses with a relatively lower power. For example, by using LS pulses with the same power of 4.81 PW, the proton in the gas can be accelerated up to 8.7 GeV, and the witness proton can be accelerated to 10.6 GeV from 0.11 GeV, which shows the overwhelming advantage over the Gaussian and LG pulse cases.

The production of broadband, terawatt terahertz (THz) pulses has been demonstrated by irradiating relativistic lasers on solid targets. However, the generation of extremely powerful, narrow-band and frequency-tunable THz pulses remains a challenge. Here, we present a novel approach for such THz pulses, in which a plasma wiggler is elaborated by a table-top laser and a near-critical density plasma. In such a wiggler, the laser-accelerated electrons emit THz radiations with a period closely related to the plasma thickness. The theoretical model and numerical simulations predict that a THz pulse with a laser–THz energy conversion of over 2.0%, an ultra-strong field exceeding 80 GV/m, a divergence angle of approximately 20° and a center frequency tunable from 4.4 to 1.5 THz can be generated from a laser of 430 mJ. Furthermore, we demonstrate that this method can work across a wide range of laser and plasma parameters, offering potential for future applications with extremely powerful THz pulses.

Polarimetry is a highly sensitive method to quantify changes of the polarization state of light when passing through matter and is therefore widely applied in material science. The progress of synchrotron and X-ray free electron laser (XFEL) sources has led to significant developments of X-ray polarizers, opening perspectives for new applications of polarimetry to study source and beamline parameters as well as sample characteristics. X-ray polarimetry has shown to date a polarization purity of less than $1.4\times {10}^{-11}$, enabling the detection of very small signals from ultrafast phenomena. A prominent application is the detection of vacuum birefringence. Vacuum birefringence is predicted in quantum electrodynamics and is expected to be probed by combining an XFEL with a petawatt-class optical laser. We review how source and optical elements affect X-ray polarimeters in general and which qualities are required for the detection of vacuum birefringence.

Laser-accelerated electrons are promising in producing gamma-photon beams of high peak flux for the study of nuclear photonics, obtaining copious positrons and exploring photon–photon interaction in vacuum. We report on the experimental generation of brilliant gamma-ray beams with not only high photon yield but also low divergence, based on picosecond laser-accelerated electrons. The 120 J 1 ps laser pulse drives self-modulated wakefield acceleration in a high-density gas jet and generates tens-of-MeV electrons with 26 nC and divergence as small as $1.51{}^{\circ}$. These collimated electrons produce gamma-ray photons through bremsstrahlung radiation when transversing a high-Z solid target. We design a high-energy-resolution Compton-scattering spectrometer and find that a total photon number of $2.2\times {10}^9$ is captured within an acceptance angle of $1.1{}^{\circ}$ for photon energies up to $16\;\mathrm{MeV}$. Comparison between the experimental results and Monte Carlo simulations illustrates that the photon beam inherits the small divergence from electrons, corresponding to a total photon number of $2.2\times {10}^{11}$ and a divergence of $7.73{}^{\circ}$.

Spatiotemporal optical vortex (STOV) pulses carrying purely transverse intrinsic orbital angular momentum (TOAM) are attracting increasing attention because the TOAM provides a new degree of freedom to characterize light–matter interactions. In this paper, using particle-in-cell simulations, we present spatiotemporal high-harmonic generation in the relativistic region, driven by an intense STOV beam impinging on a plasma target. It is shown that the plasma surface acts as a spatial–temporal-coupled relativistic oscillating mirror with various frequencies. The spatiotemporal features are satisfactorily transferred to the harmonics such that the TOAM scales with the harmonic order. Benefitting from the ultrahigh damage threshold of the plasma over the optical media, the intensity of the harmonics can reach the relativistic region. This study provides a new approach for generating intense spatiotemporal extreme ultraviolet vortices and investigating STOV light–matter interactions at relativistic intensities.

High harmonic generation (HHG) is an ideal probing source. In general, all harmonics are coupled with the corresponding input laser when generated, and for applications, they are separated using additional spectrometers. Herein, we report the angular isolation of relativistic harmonics at a predicted emission angle upon generation and, most importantly, a new phase-matching chain selection rule is derived to generate harmonics. Based on the laser plasma mechanism involving two non-collinear relativistic driving lasers, the nth harmonic carrying the information of both input lasers originates from its adjacent (n – 1)th harmonic coupled with one of the input lasers. Meanwhile, the intensity and emission angle of the generated isolated harmonic are both greatly increased compared with those in the gas scheme. These results are satisfactorily verified by theoretical analysis and three-dimensional particle-in-cell simulations, which have physical significance and are essential for practical applications.

Multidimensional instabilities always develop with time during the process of radiation pressure acceleration, and are detrimental to the generation of monoenergetic proton beams. In this paper, a sharp-front laser is proposed to irradiate a triple-layer target (the proton layer is set between two carbon ion layers) and studied in theory and simulations. It is found that the thin proton layer can be accelerated once to hundreds of MeV with monoenergetic spectra only during the hole-boring (HB) stage. The carbon ions move behind the proton layer in the light-sail (LS) stage, which can shield any further interaction between the rear part of the laser and the proton layer. In this way, proton beam instabilities can be reduced to a certain extent during the entire acceleration process. It is hoped such a mechanism can provide a feasible way to improve the beam quality for proton therapy and other applications.

The collimated electron jets ejected from cylindrical plasma are produced in particle-in-cell simulation under the applied longitudinal magnetostatic field and radial electrostatic field, which is a process that can be conveniently performed in a laboratory. We find that the applied magnetostatic field contributes significantly to the jet collimation, whereas the applied electrostatic field plays a vital role in the jet formation. The generation mechanism of collimated jets can be well understood through energy gain of the tagged electrons, and we conclude that the longitudinal momentum of the electrons is converted from the transverse momentum via the transverse-induced magnetic field. It has been found that the ejecting velocity of the jets is close to the speed of light when the applied electrostatic field reaches 3 × 1010 V/m. The present scheme may also give us an insight into the formation of astrophysical jets in celestial bodies.

A method for inertial confinement fusion driven by powerful long wavelength electromagnetic pulses (EMPs), such as ${\rm CO}_{2}$ laser pulses or high power microwave pulses, is proposed. Due to the high efficiency of generating such long wavelength electromagnetic pulses, this method is especially important for the future fusion electricity power Special fuel targets are designed to overcome the shortcomings of the long wavelength electromagnetic pulses.

Plasma wakefield excited by a short TeV-scale proton beam is investigated in the highly nonlinear regime. Analysis of the “bubble” field illustrates that transverse expelling force of the wakefield can be compensated by the attractive force, which originates from the co-propagating electrons within the proton bunch, leading to a collimation effect that stabilizes the beam propagation. The protons located in the beam tail can be well-confined and accelerated forward for a long distance. Two-dimensional simulations show that after a 1-TeV proton bunch propagating through plasma for a distance, several percentages of the protons achieve a remarkable energy gain. This scheme presents a potential that proton beams from conventional accelerators may gain considerable additional energy through plasmas wakefields.

We explore the feasibility of accelerating electron beams up to energies much beyond 1 TeV in a realistic scale and evolution of the beam qualities such as emittance and energy spread at the final beam energy on the order of 100 TeV, using the newly formulated coupled equations describing the beam dynamics and radiative damping of electrons. As an example, we present a design for a 100 TeV laser-plasma accelerator in the operating plasma density np = 1015 cm−3 and numerical solutions for evolution of the normalized emittance as well as their analytical solutions. We show that the betatron radiative damping causes very small normalized emittance that promises future applications for the high-energy frontier physics.

A laser wakefield accelerator (LWFA) with a weak focusing force is considered to seek improved beam quality in LWFA. We employ super-Gaussian laser pulses to generate the wakefield and study the behavior of the electron beam dynamics and synchrotron radiation arising from the transverse betatron oscillations through analysis and computation. We note that the super-Gaussian wakefields radically reduce the betatron oscillations and make the electron orbits mainly ballistic over a single stage. This feature permits to obtain small emittance and thus high luminosity, while still benefitting from the low-density operation of LWFA (Nakajima et al. 2011 Phys. Rev. ST Accel. Beams14, 091301), such as the reduced radiation loss, less number of stages, less beam instabilities, and less required wall plug power than in higher density regimes.

Super-luminous ionization front achieved by using axicon as focus lens is proposed to improve the transition-Cherenkov radiation of terahertz emitted from a femtosecond laser filament in air. Benefitted from the better coherent superposition of radiation electric field generated by dipole-like electron current behind the ionization front, the terahertz radiation in far zone is enhanced by one order when the velocity of ionization front exceeds the light speed. Moreover, the radiation spectrum extends toward high frequency and covers the entire terahertz gap.

Neutron production from a thin deuterium–tritium (D–T) foil irradiated by two intense femtosecond laser pulses from opposite sides with zero phase difference is studied analytically and numerically. For the interaction of a laser pulse of amplitude $a=7$, focal area 100 $\mu$m$^2$ and areal density $4.4\times 10^{18}$ cm$^{-2}$ with a D–T plasma foil, about $1.17\times 10^{21}$ neutron s$^{-1}$ can be obtained, much more than from other methods. The profiles of the ion and electron densities are also calculated.