We report the experimental measurement of millijoule terahertz (THz) radiation emitted in the backward direction from laser wakefields driven by a femtosecond laser pulse of few joules interacting with a gas target. By utilizing frequency-resolved energy measurement, it is found that the THz spectrum exhibits two peaks located at about 4.5 and 9.0 THz, respectively. In particular, the high frequency component emerges when the drive laser energy exceeds 1.26 J, at which electron acceleration in the forward direction is detected simultaneously. Theoretical analysis and particle-in-cell simulations indicate that the THz radiation is generated via mode conversion from the laser wakefields excited in plasma with an up-ramp profile, where radiations both at the local electron plasma frequency and its harmonics are produced. Such intense THz sources may find many applications in ultrafast science, e.g., manipulating the transient states of matter.

A dual-beam platform is developed for all-optical Thomson/Compton scattering, with versatile parameter tuning capabilities including electron energy, radiation energy, radiation polarization, etc. By integrating this platform with a 200 TW Ti:sapphire laser system, we demonstrate the generation of inverse Compton scattering X-/gamma-rays with tunable energies ranging from tens of keV to MeV. The polarization of X-/gamma-rays is manipulated by adjusting the polarization of the scattering laser. In the near future, by combining this platform with multi-PW laser facilities, our goal is to explore the transition from nonlinear Thomson scattering to nonlinear Compton scattering, ultimately verifying theories related to strong-field quantum electrodynamics effects induced by extreme scattering.

Vortex γ photons carrying orbital angular momenta (OAM) hold great potential for various applications. However, their generation remains a great challenge. Here, we successfully generate sub-MeV vortex γ photons via all-optical inverse Compton scattering of relativistic electrons colliding with a subrelativistic Laguerre-Gaussian laser. In principle, directly measuring the OAM of γ photons is challenging due to their incoherence and extremely short wavelength. Therein, we put forward a novel method to determine the OAM properties by revealing the quantum opening angle of vortex γ photons, since vortex particles exhibit not only a spiral phase but also transverse momentum according to the quantum electrodynamics theory. Thus, γ photons carrying OAM manifest a much larger angular distribution than those without OAM, which has been clearly observed in our experiments. This angular expansion is considered as an overall effect lying beyond classical theory. Our method provides the first experimental evidence for detecting vortex γ photons and opens a new perspective for investigating OAM-induced quantum phenomena in broad fields.

High‐charge beams remain a key research focus in laser plasma acceleration, driven by the demands of extreme experimental conditions in nuclear physics, laboratory astrophysics, and fusion research. A distinct acceleration mechanism is presented in which the interaction between petawatt femtosecond laser pulses and the subcritical density (SCD) plasma produces electron beams with charges of hundreds of nanocoulomb (nC), far exceeding those typically achieved via conventional laser wakefield acceleration. The synergy between the multiwakefield structure in SCD plasma and the laser self‐steepening effect significantly enhances the electron injection rate to 100 nC ps ⁻¹ , experimentally achieving the electron beam charge up to 245 nC. This mechanism operates by reducing the phase velocity of plasma waves and increasing electron momentum, allowing large numbers of electrons to exceed the wave‐breaking threshold and undergo efficient injection. Experiments and simulations consistently confirm the dependence of charge on plasma density and laser energy, with charge reaching a maximum at a specific plasma density. Such high‐charge, high‐density electron beams offer promising applications in high‐flux particle beam physics, large‐field‐of‐view industrial imaging, advanced light sources, and radiation‐hardness testing of electronic systems.

Although “ghost” imaging has seen remarkable advances since it was first studied 30 years ago, there have been few studies on x-ray ghost imaging (XGI) due to technical difficulties. A chief potential advantage of XGI is that imaging can be achieved with much lower radiation intensity. However, in previous XGI experiments with continuous wave x-ray illumination, the total sampling time was actually quite long, leading to additional radiation dose accumulation. In this paper, we report a proof-of-concept experiment using a high-sensitivity single-pixel detector together with a simple tabletop x-ray source followed by an adjustable mechanical shutter, which could reduce the total exposure time to as little as 5 ms. Imaging was realized with a spatial resolution of 100 μm under a low radiation dose. The influence of x-ray tube current, sampling frequency, and exposure times on image quality was examined. Our experiment illustrates a practical method for low-radiation dose ghost imaging and provides valuable reference data for the future development of medical XGI cameras.

Laser wakefield acceleration (LWFA) holds great potential in the exploration of the next-generation accelerators and future colliders, in which the injection mechanism plays a crucial role as it directly affects the characteristics of electron acceleration. Ionization injection is a continuous injection mechanism that enables producing high-charge electron beams via LWFA, at the cost of broad spectrum of the accelerated electrons. Recently, an improvement to the ionization injection mechanism has been theoretically proposed. The so-called scissor-cross ionization injection enables short injection lengths and quasi-simultaneous injection of the electrons. In this work, we experimentally demonstrate such injection mechanism, which uses an additional intense laser pulse intersecting the wakefield accelerator at an acute angle to trigger the scissor-cross ionization injection. When the time delay between the laser pulses is finely varied within the pulse duration, the method enables precise tuning of the injection process, of the charge and of the energy spread of the electron beam. Our successful demonstration of the scissor-cross ionization injection leads to a high-charge 224 MeV electron beam with energy spread below 5%.