Observation of X-ray spectra from nitrogen clusters irradiated with high-intensity ultrashort laser pulses

Abstract

X-ray spectra from nitrogen clusters irradiated with ultrashort laser pulses are reported. The line spectra of H-like and He-like nitrogen ions have been observed by irradiation with 100 fs, 800 nm pulses at 7×1017 W/cm2 irradiance. The generation of highly charged ions of N6+ and N7+ is explained by the optical field-induced ionization and the subsequent collisional ionizations in the clusters. The He-δline has anomalously high brightness compared to other He-like lines. It is ascribed to charge exchange, which preferentially populates the n=5 level of N5+.