Recoil-ion momentum spectroscopy of multiply charged argon ions produced by intense (∼1016 W cm−2) laser light

Multiple ionization processes of argon atoms by a linearly polarized laser light with the maximum peak intensity of about 5 × 1015 W cm−2 were investigated by the recoil-ion momentum spectroscopy. Momentum distributions of argon ions with charge states 3+ and 4+ were measured. The experimental results were compared with calculations based on the sequential ionization model and the ADK ionization rate [M.V. Ammosov et al., Zh. Eksp. Teor. Fiz. 91 (1986) 2008 (Sov. Phys. JETP 64 (1986) 1191)]. The calculated widths of the distributions agreed with the experimental results to within 30%.