Search

In all-optical Compton scattering driven by a multi-petawatt laser, it is critical to have accurate spatiotemporal synchronization between the ultrarelativistic electron bunch and the ultrahigh-intensity laser beam. Such a synchronization was realized by using two complementary optical setups. The first setup, used for the initial synchronization, recorded the spatial interferogram between the two femtosecond lasers used for a GeV electron beam production and an ultrahigh scattering laser beam. The second one, consisting of spatial and spectral interferometers, measured the time delay between the two laser beams in the range of 0–200 fs in real time. These monitoring systems played an essential role in conducting Compton scattering experiments. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of electron beam injection and acceleration in the bubble regime of a laser wakefield is studied experimentally. When a 50TW, 35fs laser pulse is focused to a spot size of ∼22μm (FWHM) in a tenuous 1-cm-long helium gas jet, well-collimated (a few milliradians) electron beams with energies in the sub-GeV level are produced. Multiple electron bunches are observed when the laser–plasma channel (i.e., interaction length) is long (<∼1cm). However, only one bunch is generated when the channel is short (∼2mm). These experimental results confirm the evolution scenarios of the electron bunches observed in 3D PIC simulations [refer to the publications: N. Hafz et al., Nat. Photon. 2 (2008) 571 and S. Kalmykov et al., Phys. Rev. Lett. 103 (2009) 135004], which suggested that multiple electron injections are a characteristic process for a long acceleration length and an evolving plasma bubble. [Copyright &y& Elsevier]

The phase velocity of the wakefield of a laser wakefield accelerator can, theoretically, be manipulated by shaping the longitudinal plasma density profile, thus controlling the parameters of the generated electron beam. We present an experimental method where using a series of shaped longitudinal plasma density profiles we increased the mean electron peak energy more than 50%, from 175 ± 1 MeV to 262 ± 10 MeV and the maximum peak energy from 182 MeV to 363 MeV. The divergence follows closely the change of mean energy and decreases from 58.9 ± 0.45 mrad to 12.6 ± 1.2 mrad along the horizontal axis and from 35 ± 0.3 mrad to 8.3 ± 0.69 mrad along the vertical axis. Particle-in-cell simulations show that a ramp in a plasma density profile can affect the evolution of the wakefield, thus qualitatively confirming the experimental results. The presented method can increase the electron energy for a fixed laser power and at the same time offer an energy tunable source of electrons. [ABSTRACT FROM AUTHOR]