Double ionization in gases driven by optical field ionization using ultrashort laser pulses

Rapid optical field ionization (OFI) for atoms and ions is distinguished using ultra-short laser pulses focused to peak fields comparable to Coulomb binding values. This nonperturbative field description facilitates understanding of standard sequential ionization and distinguishes the double (or two-electron ejection) ionization process. Following our discovery of double optical field ionization in He{sup +2} at 614 nm we have extended experiments to include helium, neon and argon at an 800 nm wavelength with varying ellipticity. We compare double ionization data with predictions from the semi-classical model by Corkum. New experimental results at 800 nm use 130 femtosecond laser pulses focused to intensities of order 10{sup 16} W/cm in the extraction region of a 1 meter time-of-flight spectrometer. Gas pressures ranged from 10{sup {minus}8} to 10{sup {minus}5} torr.