Density characterization of tapered super-sonic gas jet targets for laser wakefield acceleration

Phase slippage between plasma wave and electron bunch limits maximum energy gain in laser-wakefield acceleration. Plasma-density spatial tailoring has been proposed as a way to overcome this dephasing problem [1]. In practice, such tailoring can be achieved in super-sonic gas jets by use of a nozzle with a tapered orifice. We have developed a 3-D temporally-resolved interferometric tomography technique to characterize dynamical density distribution of such gas jets. The SIRT (Simultaneous Iterative Reconstructive Technique) algorithm [2] was implemented. We also present preliminarily results on laser wakefield acceleration in the tailored gradient density profiles resulting from use of the characterized jets as targets. \\[4pt] [1] W. Rittershofer, C. B. Schroeder, E. Esarey, F. J. Gr\"uner, and W. P. Leemans, ``Tapered plasma channels to phase-lock accelerating and focusing forces in laser-plasma accelerators,'' \textit{Physics of Plasmas} \textbf{17}, 063104, (2010). \\[0pt] [2] P. Gilbert, ``Iterative methods for the three-dimensional reconstruction of an object from projections,'' \textit{Journal of Theoretical Biology} \textbf{36}, 105 (1972).