Besides characteristic target and projectile x rays, x-ray continua and radiative-electron-capture photons are seen in collisions with relativistic heavy ions ranging in energy from 82 to 422MeV/amu and in atomic number from Xe to U. The angular distribution, centroid energy, cross section, and line shape of the broad radiative-electron-capture lines are analyzed. The observed continua are due to primary-and secondary-electron bremsstrahlung.In the projectile frame, primary bremsstrahlung is the radiative scattering of incident target electrons from the projectile nucleus.The continuum cross sections and angular distributions are calculated, and are compared with experiment. Secondary-electron bremsstrahlung, due to the radiative scattering of ionized target electrons from other target nuclei, is target-thickness dependent, and the cross section increases roughlỹ ith the square of the target atomic number. The calculated primary-electron bremsstrahlung cross sections are lower than experiment.

The interaction of an unpolarized electron beam with a counterpropagating ultraintense linearly polarized laser pulse is investigated in the quantum radiation-dominated regime. We employ a semiclassical Monte Carlo method to describe spin-resolved electron dynamics, photon emissions and polarization, and pair production. Abundant high-energy linearly polarized γ photons are generated intermediately during this interaction via nonlinear Compton scattering, with an average polarization degree of more than 50%, further interacting with the laser fields to produce electron-positron pairs due to the nonlinear Breit-Wheeler process. The photon polarization is shown to significantly affect the pair yield by a factor of more than 10%. The considered signature of the photon polarization in the pair's yield can be experimentally identified in a prospective two-stage setup. Moreover, with currently achievable laser facilities the signature can serve also for the polarimetry of high-energy high-flux γ photons.

X-ray studies of relativistic heavy-ion-atom collisions allow the direct observation of the radiative-electron-capture photons. The angular distribution of these photons is approximately sin 2 0 lab , because of the cancellation of electron retardation effects when the cross sections are subjected to Lorentz transformation into the laboratory frame. Comparison of measured and calculated cross sections reveals the number of equilibrium projectile K vacancies present in the solid targets, which can be compared with charge-state measurements behind the target.

The angular distribution of W-[Formula: see text], [Formula: see text] and [Formula: see text] X-rays induced by 13.1 keV bremsstrahlung has been measured at different emission angles from 110[Formula: see text] to 140[Formula: see text] at intervals of 10[Formula: see text]. The investigation of angular dependence of [Formula: see text] X-ray intensity ratios by bremsstrahlung is barely found in previous works. The [Formula: see text] X-ray yield shows isotropic emission, while the measured [Formula: see text] and [Formula: see text] X-ray yields are found to be spatially anisotropic. At last, the anisotropy parameters for [Formula: see text] and [Formula: see text] X-rays have been derived.

Target E-vacancy and L-x-ray production cross sections in collisions with relativistic (82 -670-MeV/amu) heavy ions ranging from Ne to U are measured and compared with atomic theories of inner-shell ionization based on the plane-wave Born approximation. Because the counting methods used are unique in atomic physics, careful studies of experimental uncertainties are made. Corrections to the measured cross sections due to x-ray pileup and secondary interactions in the solid targets are also discussed.

We experimentally generate a vortex beam through a four-wave mixing (FWM) process after satisfying the phase-matching condition in a rubidium atomic vapor cell with a photonic band gap (PBG) structure. The observed FWM vortex can also be viewed as the reflected part of the launched probe vortex from the PBG. Further, we investigate the propagation behaviors, including the spatial shift and splitting of the probe and FWM vortices in the medium with enhanced Kerr nonlinearity induced by electromagnetically induced transparency. This Letter can be useful for better understanding and manipulating the applications involving the interactions between optical vortices and the medium.

Generation of high-flux vortex γ -ray pulses is investigated in the interaction of ultraintense Bessel–Bessel laser bullets colliding head-on with ultrarelativistic electron bunches in the quantum radiation-dominated regime. In the simulations, a semiclassical Monte–Carlo method is used, based on the radiation probabilities in the local constant field approximation, to describe the electron motion and emission of radiation. Characteristics of the driving laser pulse (orbital angular momentum and nondiffracting spatial and temporal structures) are transferred to the emitted γ rays by nonlinear Compton scattering.

No abstract