Transverse Interferometry of a Hydrogen-Filled Capillary Discharge Waveguide

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.