Betatron radiation from direct-laser-accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S(≡n_{e}/n_{c}a_{0}). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field (a_{0}) for a fixed value of S. As a result, the total number of radiated photons scales as a_{0}^{2}/sqrt[S] and the energy conversion efficiency of photons from the accelerated electrons scales as a_{0}^{3}/S. The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.

A method of using intense Laguerre-Gaussian (LG) laser pulse is proposed to generate ultrarelativistic (multi-GeV) electron beams with controllable helical structures based on a hybrid electron acceleration regime in underdense plasmas, where both the longitudinal charge-separation electric field and transverse laser electric field play the role of accelerating the electrons. By directly interacting with the LG laser pulse, the topological structure of the accelerated electron beam is manipulated and it is spatially separated into multi-slice helical bunches. These results are clearly demonstrated by our three-dimensional particle-in-cell simulations and explained by a theoretical model based on electron phase-space dynamics. This novel regime offers a new degree of freedom for manipulating ultrashort and ultrarelativistic electrons, and it provides an efficient way for generating high-energy highangular-momentum helical electron beams, which may find applications in wide-ranging areas.

Ion acceleration in near-critical plasmas driven by intense laser pulses is investigated theoretically and numerically. A theoretical model has been given for clarification of the ion acceleration dynamics in relation to different laser and target parameters. Two distinct regimes have been identified, where ions are accelerated by, respectively, the laser-induced shock wave in the weakly driven regime (comparatively low laser intensity) and the nonlinear solitary wave in the strongly driven regime (comparatively high laser intensity). Two-dimensional particle-in-cell simulations show that quasi-monoenergetic proton beams with a peak energy of 94.6 MeV and an energy spread 15.8% are obtained by intense laser pulses at intensity I0 = 3 × 1020 W/cm2 and pulse duration τ = 0.5 ps in the strongly driven regime, which is more advantageous than that got in the weakly driven regime. In addition, 233 MeV proton beams with narrow spread can be produced by extending τ to 1.0 ps in the strongly driven regime.