High-energy negative ions from expansion of high-temperature femtosecond laser plasma

The atomic, charge and energy distributions of ions in expanding femtosecond laser plasmas have been studied by means of time-of-flight mass–charge spectroscopy. High-energy negative and positive ions with energies of up to 35 keV have been detected during the interaction of 200-fs laser pulses (I2×10¹⁶ W/cm²) with silicon, titanium and other solid targets. A high correlation between negative and positive single-charged ions of the identical atomic number is shown. Negative ions are produced as a result of collisions of fast single-charged ions and neutrals with molecules of residual gas. PACS 52.50.Jm; 52.70.Nc; 52.38.Ph