Production of highly-charged ions by nitrogen gas target irradiated with ultrashort high-intensity pulse laser

Abstract

High-density nitrogen gas was irradiated with an ultrashort high-intensity pulse laser (pulse width: 1.5 ps, intensity:≥ 10 ^{15} W/cm ^{2} ). It was found that highly charged ions were produced effectively as the gas density became higher. From distribution of population densities of high-lying levels of lithium like nitrogen ions, the electron temperature in a recombining phase was estimated. This electron temperature together with a calculation using a collisional-radiative model, in which doubly excited levels of beryllium like ions are included, indicated that the electron density was n_{e} = 3× 10 ^{19} cm ^{-3} . Moreover, the spectra also showed that population inversions between some excited states of hydrogen-, helium-, lithium like nitrogen ions were generated under this plasma conditions.