Short-pulse laser propagation in a tunnel ionizing plasma and subsequent electron acceleration

We investigate the propagation of an intense short pulse laser of Gaussian radial profile in a tunnel ionizing gas and its subsequent role in electron acceleration to high energy. The interaction region in gas is followed by the vacuum region. The laser tunnel ionizes the gas and forms a high-density plasma on the propagation axis, which causes the laser defocusing. This laser defocusing reduces the deceleration of the electron. As a result, the interacting electron gains net energy. If the laser pulse duration is long enough, then the electron-ion recombination effect may be crucial. The divergence of the laser beam is significantly affected, and hence the net energy gain is affected for the specific parameter region. A theoretical model for laser defocusing in tunnel ionizing gas including the role of electron-ion recombination is discussed. The electron energy estimation in this regime has been studied for the gas-jet experiments.