High kinetic energy release upon dissociation and ionization of an N₂⁺ beam by intense few-cycle laser pulses

The kinetic energy release (KER) and angular distribution for dissociation and ionization of N₂⁺ in an intense short pulse (7 fs) laser at 790 nm was measured by employing a coincidence three-dimensional momentum imaging method that provides kinematically complete information on the dissociation. At an intensity of 6.0×10¹⁵ W∕cm² a high-KER peak (∼6.1 eV) unexpectedly appears in the dissociation spectrum in addition to the usual low-KER peak (∼0.6 eV). Additionally, the KER distribution in ionization, which peaks around 7 eV, has a tail that surprisingly extends well beyond the Coulomb explosion energy. Both these high-KER contributions result from dissociation pathways involving highly excited states of N₂⁺ with steep potential curves as indicated by the dressed state potential energy curves picture.