Optimizing high-harmonic-generation in absorbing gases

Summary form only given. The efficiency of High-Harmonic-Generation (HHG) depends on the single atom response, on phase matching and on defocusing of the fundamental laser beam. The single atom response can be optimized and, in the loose focus/short pulse regime, phase matching can be achieved. Self defocusing is prevented here by using short pulses. As high harmonics can now coherently built up over long interaction lengths, we show that re-absorption of the harmonics by the emitting gas becomes a major limitation for HHG.