Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Transverse interferometric measurements are presented of the plasma channel formed in a hydrogen-filled capillary discharge waveguide recently used to generate 1 GeV electrons in a laser-driven plasma accelerator for the first time. The measurements were found to be in good agreement with nonlocal thermal equilibrium simulations, but showed significant differences with the results of a quasistatic model developed by Bobrova et al. [Phys. Rev. E. 65, 016407 (2001)]. The measurements are used to determine scaling laws for the axial electron density and matched spot size of the plasma channel, enabling optimization of the channel to specific applications.

Abstract:

The use of counterpropagating laser pulses to suppress high harmonic generation (HHG) is investigated experimentally for pulses polarized parallel or perpendicular to the driving laser pulse. It is shown for the first time that perpendicularly polarized pulses can suppress HHG. The intensity of the counterpropagating pulse required for harmonic suppression is found to be much larger for perpendicular polarization than for parallel polarization, in good agreement with simple models of the harmonic suppression. These results have applications to quasi-phase-matching of HHG with trains of counterpropagating pulses. © 2007 Optical Society of America.