Coulomb explosion dynamics of N 2 in intense laser field by mass-resolved momentum imaging

Abstract

The Coulomb explosion reactions of N 2, N 2 ( p+ q)+ → N p+ +N q+ , caused by the irradiation of intense laser light (0.73–6.9 PW/cm 2) were investigated by high-resolution time-of-flight (TOF) mass spectroscopy and by the mass-resolved two-dimensional momentum imaging (MRMI) method. Six explosion pathways ( p, q)=(1, 1), (1, 2), (1, 3), (2, 2), (2, 3) and (3, 3) in addition to (0, 1), (0, 2) dissociation pathways were identified, whose assignments were securely performed both from the momentum matching between the fragment pair and their correlation with the laser-field intensity dependence. The MRMI method, which visualizes the radial and angular momentum distributions of mass-selected fragment ions on a two-dimensional momentum plane, was used to correlate ion fragments produced after the Coulomb explosion. By examining theoretically synthesized MRMI maps, it was found that the momentum distributions of the fragment ions in a wide momentum range can be extracted by the MRMI technique. The relative yields of the explosion pathways at six different laser-field intensities were evaluated from the three-dimensional integration of the MRMI maps, and the intensity dependence of the formation of singly and multiply charged parent N 2 ( p+ q)+ ions prior to the fragmentation was derived.