Seventy-first harmonic generation from doubly charged ions in preformed laser-ablation vanadium plume at 110 eV

We have demonstrated a generation of 71(st) harmonic at a photon energy of 110 eV (wavelength 11.2 nm) using low ionized vanadium ions in a laser-ablation plume. The conversion efficiency of this harmonic was estimated to be 1.6x10(-7). Such high harmonic generation occurred from the interaction of a femtosecond laser pulse with a doubly charged ion, which has high third ionization potential. This work shows the extension of HHG cutoff energy can be achieved by using the doubly charged ion.