Multiple ionization of Ne and Ar by intense 25 fs laser pulses:: few-electron dynamics studied with ion momentum spectroscopy

Momentum distributions of Ne2-5+ and Ar2-7+ ions created by 795 nm, 25 fs laser pulses at intensities of up to 20 PWcm(-2) have been measured using a 'reaction microscope'. The experimental results indicate that below 2.0 PW cm(-2) the production of Ne3-4+ ions is dominated by n-fold electron impact ionization (e, ne) collisions of the recolliding electron with its parent ion. Multiple ionization of Ar is found to be dominated by mechanisms involving a combination of recollision-induced and field-induced steps as well as intermediate excitations in the whole range of intensities where non-sequential ionization occurs. Whereas a clear double peak structure characteristic for electron recollision was observed in the momentum distributions of up to Ne5+, no signatures of non-sequential ionization were found in the spectra of Ar ions with the charge state higher than 4.