Ionization of noble gases with pulses directly from a laser oscillator

A Ti:sapphire oscillator with an extended cavity generates pulses with 0.5 μJ energy at a repetition rate of 6 MHz and pulse durations of 50 fs. Tight focusing creates peak intensities exceeding 1014 W/cm2, which is sufficient for ionizing helium, a nonlinear process where at least 17 photons are absorbed simultaneously