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Laser wakefield acceleration of 500 MeV to 1 GeV electron bunches has been demonstrated using ionization injection in mixtures of 4% to 10% of CO2 in He. 80 TW laser pulses were propagated through 5 mm gas jet targets at electron densities of 0.4-1.5×1019cm-3. Ionization injection led to lower density thresholds, a higher total electron charge, and an increased probability of producing electrons above 500 MeV in energy compared to self-injection in He gas alone. Electrons with GeV energies were also observed on a few shots and indicative of an additional energy enhancement mechanism. [ABSTRACT FROM AUTHOR]

The generation of an electron beam through longitudinal field acceleration from a tightly focused radially polarized (TM01) laser mode is reported. The longitudinal field is generated by focusing a TM01 few-cycle laser pulse (1.8 μm, 550 μJ, 15 fs) with a high numerical aperture parabola. The created longitudinal field in the focal region is intense enough to ionize atoms and accelerate electrons to 23 keV of energy from a low density oxygen gas. The characteristics of the electron beam are presented. [ABSTRACT FROM AUTHOR]