Frustrated Tunnel Ionization with Few-cycle Pulses

Frustrated tunnel ionization (FTI) is one of the dominant channels in strong field ionization that results in the excitation of atoms. Recent studies have shown that there is a significant number of FTI events for multi-cycle pulses with the theory predicting that the excitation efficiency increases with pulse duration decreasing into the few-cycle regime. Our work concentrates on experimentally investigating the effect of few-cycle pulses on the FTI excitation process. We use pulses with duration 6 fs centred at 800 nm at intensities up to 0.8 PW crossed with an atomic Ar beam. We find that with few-cycle pulses there is more FTI per tunneling event and that for the same pulse energy more FTI is generated.