All-Optical Injection AAC, Santa Fe, NM, 2000 All-Optical Injection Donald Umstadter Supported by the High-Energy Physics Division of the U.S. Department of Energy and the National Science Foundation.

Low-divergence Self-trapped MeV Beam Zero to MeV in less than 10 microns! Experimental setup. A terawatt-peak-power laser pulse is focused onto a Helium gas jet with a peak laser intensity of > 1018 W/cm2. Left: The experimental apparatus is in a vacuum chamber to prevent break down of air by the intense laser pulses. Right: The laser beam can be seen traversing the vacuum chamber to a curved mirror which focuses it to high intensity at the location of the nozzle of a gas jet. A sheet of paper blocks the laser beam transmitted through the gas jet, but the electron beam, which is accelerated by a wakefield plasma wave, is transmitted through the paper to a fluorescent screen (making the the green spot). Lower: The data shows that as the laser power increases, the electron beam divergence angle decreases to the point where the electrons are emitted with in a 1-degree angle. The decrease is due to relativistic self-focusing of the laser beam, caused by the change in the plasma index of refraction, due to the mass change of electrons in the laser focus. This corresponds to the lowest emittance of any electron gun. One nanocoulomb of charge is accelerated to a few MeV, with some electrons in the tail of the distribution reaching 100 MeV.  = 1 1010 e-

Electron beam profiles for various laser powers: multiple components Phys. of Plasmas, 7, 403 (2000).

Two-temperature Distribution

Slope of Distribution “Jumps” with Density or Laser Power

Laser Injected Laser Accelerator: LILAC

Various LILAC Concepts D. Umstadter et al., Phys. Rev. Lett. 76, 2073 (1996). Ponderomotive kick w/ or w/o ionization E. Esarey et al., Phys. Rev. Lett. 79, 2682 (1997). Beatwave ponderomotive kick B. Rau et al., Phys. Rev. Lett. 78, 3310 (1997). Half-cycle pulse, sharp density gradient R. G. Hemker et al., Phys. Rev. E 57, 5920 (1998). Colliding wakes S.V. Bulanov, Plasma Phys. Rep. 25, 468 (1999). Sharp density gradient C.I. Moore et al., Phys. Rev. Lett. 82, 1688 (1999). Ionization

150-terawatt Laser Construction. Preamplifier and cleaner Large aperture high energy (~100mJ) regenerative amplifier 15J green pump laser.

Current kHz Laser Intensity Pulse Duration Pulse Energy 3x1018 W/cm2 Pulse Duration 8 to 21 fs Pulse Energy 3 mJ (21fs) Focal Spot Size 1mm 1.2 mm Intensity Efocused/Etotal=83%

Summary of Our Experimental Observations Electron acceleration in a relativistically self-guided plasma channel Electron beam: D = 1°, e = 0.06 p mm-mrad Multiple electron beam components explained Relativistic filamentation and electron acceleration w/o significant Raman scatter Proton Acceleration by vacuum heating Measured acceleration gradients 2 GeV/cm (108 A/cm2)