Multiphoton ionization of molecular nitrogen by a neodymium-glass laser

Multiphoton ionization of molecular nitrogen N₂ is investigated by using a neodymium-glass laser. The atomic ions N⁺ and the molecular ions N₂^_⁺ produced during the interaction are separated by a time-of-flight analyzer and collected on the cathode of an ion multiplier. The experimental results give the values 9±{}1 for the nonlinear interaction order for N₂^_⁺ and 12±{}1 for N⁺, and then lead to the determination of separate probabilities of multiphoton formation of N₂^_⁺ and N⁺; for a flux value of 2.44×{}10¹² W/cm², these probabilities are, respectively, 3×{}10^6±0.7 sec^-1 and 2×{}10^7±0.7 sec^-1. The multiphoton excitation, ionization, and dissociation processes of N₂ are discussed.