Gas jet structure influence on high harmonic generation.

Gas jets used as sources for high harmonic generation (HHG) have a complex three-dimensional density and velocity profile. This paper describes how the profile influences the generation of extreme-UV light. As the position of the laser focus is varied along the jet flow axis, we show that the intensity of the output radiation varies by approximately three times, with the highest flux being observed when the laser is focused into the Mach disc. The work demonstrated here will aid in the optimization of HHG flux from gas jet sources. The flux increase is attributed to a density increase within the structure of the jet, which is confirmed by simultaneous imaging of atom and ion fluorescence from the jet.