A novel approach for positron injection and acceleration in the laser driven plasma wakefield is proposed. One ring-shaped beam and one coaxially propagating Gaussian beam drive wakefields in a preformed plasma volume filled with both electrons and positrons. The laser's ponderomotive force as well as the charge separation force in the front bucket of the first bubble are utilized to provide the transverse momenta of injected positrons and those positrons can be trapped by the focusing field and then accelerated by the wakefield. Theoretical analysis of the process is presented and verified by particle-in-cell simulations. The simulations show that relatively high-charge, quasimonoenergetic positron beams can be obtained.

Compact short pulse positron source in the energy range of a few tens of MeV driven by laser plasma accelerator is a promising tool for many applications, such as materials science and source of colliders. A collection and transmission system based on laser plasma accelerators is proposed to intensify and narrow the beam divergence for positrons generated from converters. The system is composed of a converter, a collimator, a solenoid, quadrupoles, and a slit in the exit. Numerical simulations were performed to demonstrate the feasibility and robustness of the design. The designed system can work in the center energy range from 15 to 40 MeV within ±10% energy spread (FWHM) and greatly improve the quality of collected positron beams with a divergence of around 50 mrad.

Direct imaging is a key tool for diagnostics of density transition in different material composition. Ultrafast electron bunches from 100 TW‐level laser system are attractive in future applications. Experiments for direct imaging with 100 MeV electrons are conducted using a 200 TW laser facility in Peking University. Electron bunches with energy spectra ranging from 100 to 150 MeV are achieved with a mixture gas of 0.5% nitrogen and 99.5% helium. Herein, the contrast imaging, transmission, and slit experiments are conducted and analyzed. It turns out the superiority of the hundreds of MeV electrons in thick material imaging applications. It is also anticipated that this technology can be used for ultrafast dynamic analysis with the advent of higher charge electrons in a single ultrafast bunch from laser‐driven electron accelerators.

A compact electron radiography system has been designed with high gradient permanent magnet quadrupoles with 2.5 times magnification. Quasi-monoenergetic electron bunches with energies ranging from 100 to 200 MeV are generated from a laser wakefield accelerator (LWFA) acting as the electron source for the system. A matching segment composed of three quadrupoles before the objective plane creates a correlation between the position and the angle for the electrons, illuminating the observed object improved the resolution of the system. We expect electron radiography with 100-MeV ultrafast electron bunches to be widely adopted for many applications, especially considering the micron-level spatial resolution and sub-picosecond temporal resolution of the electron source from the LWFA. Since the laser system needed for generating 100–200 MeV electrons using the LWFA is roughly around 40 TW, the whole system can be effectively table-top in size, which is favorable for movable applications.