Resonance enhancement of single even harmonic of laser radiation in tin-containing plasma using intensity variation of two-color pump

We show that, in the case of a two-color pump, the plasma plumes of tin and tin-containing alloy targets produce an enhanced 18th harmonic of a Ti:sapphire laser. More than a tenfold enhancement of the 18th harmonic compared to the neighboring harmonic orders was achieved by optimizing the position of the focal plane of the two-color pump with respect to the plasma plume. The detuning between the enhanced 17th and 18th harmonics was demonstrated by changing the focusing conditions, which allows one to manipulate the conversion efficiency of the 18th harmonic.