High-order harmonic generation in laser-produced ions

Abstract
We have investigated the high-order harmonic generation of a subpicosecond KrF laser (248 nm) using nine ionic species in laser-produced plasmas. The highest order of the 21st harmonic (11.8 nm) has been observed in a lead plasma. The maximum observed harmonic orders in various ions and neutral rare gases are found to be proportional to the ionization potentials of these species. We have obtained superior results for the high-order harmonic generation by using ions compared to using neutral rare gases, and have demonstrated the advantages of using ions as nonlinear media to generate extreme ultraviolet radiation.