Resonance-Enhanced Multiphoton Ionization of Molecular Oxygen at the 222 nm KrCl Laser Wavelength

We study the photo-ionization mechanism of molecular oxygen at the 222 nm KrCl laser wavelength within a laser pulse intensity range of 10 8 – 10 10 W/cm 2 , using 14 ns laser pulses. We experimentally observe (2+1) resonance-enhanced multiphoton ionization (REMPI) of molecular oxygen with the effective ionization cross-section σ O 2 2 = (3 . 2 ± 1 . 3) · 10 − 18 cm 4 · s − 1 · W − 2 at an intensity range of 10 9 – 10 10 W/cm 2 and linear ionization due to gas impurities at an intensity range of 10 8 – 10 9 W/cm 2 .