High energy electrons from interaction with a 10 mm gas-jet at FLAME

In this paper we discuss the spectra of the electrons produced in the laser-plasma acceleration experiment at FLAME. Here a < 30 fs laser pulse is focused via an f/10 parabola in a focal spot of 10 μm diameter into a 1.2 mm by 10 mm rectangular Helium gas-jets at a backing pressure ranging from 5 to 15 bar. The intensity achieved exceeds 1019 Wcm-2. In our experiment the laser is set to propagate in the gas-jet along the longitudinal axis to use the 10 mm gas-jet length and to evaluate the role of density gradients. The propagation of the laser pulse in the gas is monitored by means of a Thomson scattering optical imaging. Accelerated electrons are set to propagate for 47,5 cm before being detected by a scintillating screen to evaluate bunch divergence and pointing. Alternatively, electrons are set to propagate in the field of a magnetic dipole before reaching the scintillating screen in order to evaluate their energy spectrum. Our experimental data show highly collimated bunches (< 1 mrad) with a relatively stable pointing direction (< 10 mrad). Typical bunch electron energy ranges between 50 and 200 MeV with occasional exceptional events of higher energy up to 1GeV. © 2013 SPIE.