Field intensity dependence of the dissociative multiple ionization of argon dimers in strong femtosecond laser fields

The dissociative ionization of Ar dimers is investigated in femtosecond laser fields with intensities from 260 to 1020 TW/cm². The three-dimensional momentum and kinetic-energy release of fragmental ions generated from the channels Ar₂²⁺→Ar⁺+Ar⁺, Ar₂³⁺→Ar²⁺+Ar⁺, and Ar₂⁴⁺→Ar²⁺+Ar²⁺ were measured with a cold-target recoil-ion momentum spectrometer. It is shown that the laser intensity significantly modulates the kinetic energies and angular distributions of fragmental ions from dissociative double ionization. Laser-induced charge-transfer following one-site double ionization contributes relatively more to the dissociative double ionization at lower laser intensity. The calculation results of a one-dimensional model based on the WKB approximation suggest that the charge transfer is suppressed at higher laser intensity due to the core polarization effect. In addition, double, triple, and quadruple dissociative ionizations of Ar dimers are accompanied by frustrated-tunneling ionization that increases with the laser intensity.