The average degree of ionization for a Xe cluster irradiated by lasers of pulse durations 2T0 (a) and 8T0 (b)
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Figure 6. The average degree of ionization for a Xe cluster irradiated by lasers of pulse durations 2T0 (a) and 8T0 (b). Solid blue and red dot–dashed lines correspond to CE phases of = 0 and = π/2, respectively. The laser intensity is the same as used in figure 1. For these calculations, collisional ionization is artificially switched off.
A three-dimensional molecular dynamic approach is employed to investigate the ionization dynamics of small Xe400 clusters irradiated by intense lasers (I = 1016W cm−2) in the near infrared wavelength region (λ = 800 nm). The pulse duration of the incident laser is varied from a few cycles (τ = 2T0 with T0 as one laser time cycle) to many cycles (τ = 8T0). In the case of pulse durations of a few cycles, the carrier–envelope (CE) phase of the incident laser electric field is found to be an important parameter that affects the ionization dynamics of Xe clusters. The fractions of various ionized Xe species are observed to be different for the two values of the CE phases ( = 0 and = π/2) in the case of the shorter laser pulse duration of τ = 2T0. The nature of the instantaneous electric field (the rising or falling edge of the field) at the time of birth of the electron due to ionization decides the extent of ionization. The difference in time-evolution of the electric field for the two values of the CE phase leads to an observable disparity in the yield of various ionic species. For the case of a pulse duration of many cycles (τ = 8T0), these differences average out and we do not observe any change in the yield of various ionic species for the two values of the CE phase.