Electron acceleration by few-cycle laser pulses with single-wavelength spot size

Generation of relativistic electrons from the interaction of a laser pulse with a high density plasma foil, accompanied by an underdense preplasma in front of it, has been studied with two-dimensional particle-in-cell (PIC) simulations for pulse durations comparable to a single cycle and for single-wavelength spot size. The electrons are accelerated predominantly in forward direction for a preplasma longer than the pulse length. Otherwise, both forward and backward electron accelerations occur. The primary mechanism responsible for electron acceleration is identified. Simulations show that the energy of the accelerated electrons has a maximum versus the pulse duration for relativistic laser intensities. The most effective electron acceleration takes place when the preplasma scale length is comparable to the pulse duration. Electron distribution functions have been found from PIC simulations. Their tails are well approximated by Maxwellian distributions with a hot temperature in the MeV range.