High kinetic energy release upon dissociation and ionization of anN2+beam by intense few-cycle laser pulses

Abstract

The kinetic energy release (KER) and angular distribution for dissociation and ionization of $\mathrm{N}_{2}{}^{+}$ in an intense short pulse $(7\phantom{\rule{0.3em}{0ex}}\mathrm{fs})$ laser at $790\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ was measured by employing a coincidence three-dimensional momentum imaging method that provides kinematically complete information on the dissociation. At an intensity of $6.0\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ a high-KER peak $(\ensuremath{\sim}6.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ unexpectedly appears in the dissociation spectrum in addition to the usual low-KER peak $(\ensuremath{\sim}0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. Additionally, the KER distribution in ionization, which peaks around $7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, 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 $\mathrm{N}_{2}{}^{+}$ with steep potential curves as indicated by the dressed state potential energy curves picture.