• D.H. Froula, J. Bonlie, L. Divol, S.H. Glenzer, P. Michel, J. Palastro, D. Price, J.E. Ralph, J.S. Ross, C. Siders
  LLNL, Livermore, California
• C.E. Clayton, C. Joshi, K.A. Marsh, A.E. Pak
  UCLA, Los Angeles, California
• B.B. Pollock, G.R. Tynan
  UCSD, La Jolla, California

Funding: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and DE-FG03-92ER40727, and LDRD 06-ERD-056

Recent laser wakefield acceleration experiments at the Jupiter Laser Facility, Lawrence Livermore National Laboratory, will be discussed where the Callisto Laser has been upgraded and has demonstrated 60 fs, 10 J laser pulses. This 150 TW facility is providing the foundation to develop a GeV electron beam and associated betatron x-ray source for use on the petawatt high-repetition rate laser facility currently under development at LLNL. Initial self-guided experiments have produced high energy monoenergetic electrons while experiments using a multi-centimeter long magnetically controlled optical plasma waveguide are investigated. Measurements of the electron energy gain and electron trapping threshold using 150 TW laser pulses will be presented.

• B.B. Pollock, J.S. Ross, G.R. Tynan
  UCSD, La Jolla, California
• C.E. Clayton, C. Joshi, K.A. Marsh, A.E. Pak, T.-L. Wang
  UCLA, Los Angeles, California
• L. Divol, D.H. Froula, S.H. Glenzer, V. Leurent, J. Palastro, J.E. Ralph
  LLNL, Livermore, California

We present experimental results showing the formation of a laser produced optical waveguide, suitable for laser guiding, when applying a high external magnetic field around a gas cell. This technique is directly applicable to wakefield acceleration and has been established at the Jupiter Laser Facility; an external magnetic field prevents radial heat transport, resulting in an increased electron temperature gradient [D. H. Froula et.al., Plasma Phys. Control. Fusion, 51, 024009 (2009)]. Interferometry and spatially resolved Thomson-scattering diagnostics measure the radial electron density profile, and show that multiple-centimeter long waveguides with minimum electron densities of 10¹⁷ to 10¹⁸ cm^-3 can be produced. Temporally resolved Thomson-scattering is also performed to characterize the evolution of the density channel in time. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was partially funded by the Laboratory Directed Research and Development Program under project tracking code 06-ERD-056.

• J.E. Ralph, F. Fang, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, A.E. Pak, F.S. Tsung
  UCLA, Los Angeles, California

Funding: This work was supported by The Department of Energy Grant No.DEFG02-92ER40727.

The self-guiding of relativistically intense but ultra-short laser pulses has been experimentally investigated as a function of laser power, plasma density and plasma length in the so-called "blowout" regime. Although etching of the short laser pulse due to diffraction and local pump depletion erodes the the head of the laser pulse, an intense portion of the pulse is guided over tens of Rayleigh lengths, as observed by imaging the exit of the plasma. Spectrally-resolved images of the laser pulse at the exit of the plasma show evidence for photon acceleration as well as deceleration (pump depletion)in a well defined narrow guided region. This is indicative of the self-guided pulse residing in the wake excited in the plasma. Energy outside the guided region was found to be minimized when the initial conditions at the plasma entrance were closest to the theoretical matching conditions for guiding in the blowout regime. The maximum extent of the guided length is shown to be consistent with the nonlinear pump depletion length predicted by theory.