Comparative investigation of third and fifth harmonic generation in   atomic and molecular gases driven by mid-infrared ultrafast laser pulses
  We report on the comparative experimental investigation on third and fifth harmonic generation (THG and FHG) in atomic and molecular gases driven by mid-infrared ultrafast laser pulses at a wavelength of ~1500 nm. We observe that the conversion efficiencies of both the THG and FHG processes saturate at similar peak intensities close to ~1.5\times1014 W/cm2 for argon, nitrogen, and air, whose ionization potentials are close to each other. Near the saturation intensity, the ratio of yields of the FHG and THG reaches ~10-1 for all the gases. Our results show that high-order Kerr effects do exist, whereas they are insufficient to balance the Kerr self-focusing without the assistance of plasma generation. 
Jielei Ni, Jinping Yao, Bin Zeng, Wei Chu, Guihua Li, Haisu Zhang,   Chenrui Jing, See Leang Chin, Ya Cheng, Zhizhan Xu
physics.optics physics.atom-ph