Spatial effects in the intense field ionization of N₂ molecules by femtosecond-duration laser pulses

Abstract

Spatially resolved time-of-flight measurements have been made of laser-induced multiple ionization of N₂ molecules in intensity-selective fashion using 100 fs long light pulses of 806 nm wavelength, over an intensity range 10¹³-10¹⁵ W cm^-2. The spatial dependence of the laser intensity within the laser-molecule interaction zone determines the overall ionization dynamics. Different processes are shown to dominate in different intensity (spatial) regimes, leading to an inhomogeneous distribution of N₂⁺ and N^q+ (q1) ions and their kinetic energies in the laser focal volume. Implications are discussed for experiments that aim to probe phenomena such as bond softening and above-threshold dissociation.