Enhancement of harmonics and parametric waves in the extreme ultraviolet region during propagation of femtosecond pulses through the La, Yb, and Gd laser-induced plasmas

High-order harmonic generation in three lanthanide-containing plasmas using different pumping schemes is analyzed. We demonstrate different methods of enhancement of the harmonics and parametric waves in La, Yb, and Gd plasmas. The resonance-induced growth of intensity for a few harmonics in the La and Yb plasmas, with an enhancement factor up to 8, is observed. The high spatial coherence of resonance-enhanced harmonics is demonstrated. These studies show the dramatic modification of the harmonic distribution generated in the studied species during variation of the plasma components from containing mostly neutrals to comprising a large concentration of ions.