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

Abstract

We study the photo-ionization mechanism of molecular oxygen at the 222 nm KrCl laser wavelength within a laser pulse intensity range of 108 – 1010 W/cm2, using 14 ns laser pulses. We experimentally observe (2+1) resonance-enhanced multiphoton ionization (REMPI) of molecular oxygen with the effective ionization cross-section {sigma}_{{mathrm{O}}_2}^{(2)} = (3.2 ± 1.3) · 10−18 cm4 · s−1 · W−2 at an intensity range of 109 – 1010 W/cm2 and linear ionization due to gas impurities at an intensity range of 108 – 109 W/cm2.