Amplification of Relativistic Electron Bunches by Acceleration in Laser Fields

Attosecond gamma-ray flashes and electron-positron pairs in dyadic laser interaction with microwire

The interaction of an ultra-intense laser with matter is an efficient source of high-energy particles, with efforts directed toward narrowing the divergence and simultaneously increasing the brightness. In this paper we report on emission of highly collimated, ultrabright, attosecond γ-photons and generation of dense electron-positron pairs via a tunable particle generation scheme, which utilizes the interaction of two high-power lasers with a thin wire target. Irradiating the target with a radially polarized laser pulse first produces a series of high charge, short duration, electron bunches with low transverse momentum. These electron bunches subsequently collide with a counter-propagating high-intensity laser. Depending on the intensity of the counter-propagating laser, the scheme generates highly collimated ultra-bright GeV-level γ-beams and/or electron-positron plasma of solid density level.

Diagnosis of ultrafast surface dynamics of thin foil targets irradiated by intense laser pulses

The temporal modulation of an electron bunch train accelerated from a foil target irradiated by an intense laser pulse is studied by measuring the coherent transition radiation (CTR) from the rear surface of a target. We experimentally obtained CTR spectra from a 1 µm thick foil target irradiated at a maximum intensity of 6.5 × 10¹⁹ W/cm². Spectral redshifts of the emitted radiation corresponding to increases in laser intensity were observed. These measurements were compared with the theoretical calculation of CTR spectra considering ultrafast surface dynamics, such as plasma surface oscillation and relativistically induced transparency. Plasma surface oscillations induce a spectral redshift, while relativistic transparency causes a spectral blueshift. Both effects are required to find reasonable agreement with the experiment over the entire range of laser intensities.

Vacuum laser acceleration of super-ponderomotive electrons using relativistic transparency injection

Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to 20 MeV using the relativistic transparency effect. When a high-contrast intense laser drives a thin solid foil, electrons from the dense opaque plasma are first accelerated to near-light speed by the standing laser wave in front of the solid foil and subsequently injected into the transmitted laser field as the opaque plasma becomes relativistically transparent. It is possible to further optimize the electron injection/acceleration by manipulating the laser polarization, incident angle, and temporal pulse shaping. Our result also sheds light on the fundamental relativistic transparency process, crucial for producing secondary particle and light sources.

Compact electron accelerators based on laser-plasma acceleration scheme may be useful for future light sources, radiation therapy etc. Here the authors demonstrate electron acceleration in laser plasma interaction via vacuum laser acceleration and relativistic transparency injection.

Charge-Transfer Processes in Warm Dense Matter: Selective Spectral Filtering for Laser-Accelerated Ion Beams

We investigate, both experimentally and theoretically, how the spectral distribution of laser accelerated carbon ions can be filtered by charge exchange processes in a double foil target setup. Carbon ions at multiple charge states with an initially wide kinetic energy spectrum, from 0.1 to 18 MeV, were detected with a remarkably narrow spectral bandwidth after they had passed through an ultrathin and partially ionized foil. With our theoretical calculations, we demonstrate that this process is a consequence of the evolution of the carbon ion charge states in the second foil. We calculated the resulting spectral distribution separately for each ion species by solving the rate equations for electron loss and capture processes within a collisional radiative model. We determine how the efficiency of charge transfer processes can be manipulated by controlling the ionization degree of the transfer matter.