Currently, isolated attosecond pulses(IAPs) are mainly produced by the high harmonic generation(HHG) of few-cycle driving laser pulses in gas. However, the IAP energy is limited by the low efficiency of HHG as well as the low energy of the few-cycles driving laser pulse. Here, we present a novel approach named as pumping ionizing gating (PIG) to generate IAPs by picosecond driving(pump) pulse^. In this regime, a short laser is used to ionize a pre-existing gas grating, creating a fast-extending plasma grating(FEPG) having an ionization front propagating with the velocity of light. A low-intensity long counterpropagating pump pulse is then reflected by a very narrow region of the ionization front, only where the Bragg conditions for resonant reflection is satisfied. Consequently, the pump reflection is confined within a sub-cycle region called PIG, and forms a wide-band coherent IAP. Three-dimensional particle-in-cell simulations show that a 1.6-ps, 1-μm pump pulse can be used to generate a 330 as laser pulse with a peak intensity approximately 33 times that of the pump and a conversion efficiency of around 0.1%. These results show a potential to produce joule-level IAPs.
 

isolated attosecond pulses,,plasma grating,ionizing gating