Optical field-ionization of a neutral gas with inhomogeneous density for electron acceleration by a high-intensity laser

A scheme for the laser-induced acceleration of an electron from a double-ionizing neutral gas is investigated, where an inhomogeneous neutral gas profile (resembling a gas-jet experiment) is considered in order to observe the actual electron energy gain during acceleration. Optical-field ionization of the neutral gas can defocus the laser pulse significantly, and an electron accelerates by being pushed in front of a laser pulse in vacuum, and then decelerates due to the defocused (quite low-intensity) tail part of the laser pulse. The reduction in electron deceleration incurred by defocusing the laser-induced double-ionization of the neutral gas makes the electron acceleration continuous. In this study, we introduced an inhomogeneous gas profile that resembles a laser gas-jet experiment. However, the inhomogeneity of the gas reduced the rate of tunnel ionization, which limited the defocusing of the laser pulse; thus, though the electron energy gain is reduced but this proposal is more feasible and realistic. (C) 2012 American Institute of Physics. [doi:10.1063/1.3678202]