Comment on arXiv:1105.6334 "Optical nonlinearity in Ar and N$_2$ near   the ionization threshold"
  In a recent publication [Phys. Rev. Lett. 107, 103901 (2011)], Wahlstrand et al. reported to observe no indications for the appearance of the higher-order Kerr effect in a parameter regime that was previously found to display this phenomenon [Opt. Express 17, 13429 (2009)]. Here we show that careful analysis of the original experimental data of Wahlstrand et al. reveals a 22% saturation, i.e., direct proof for the appearance of the higher-order Kerr effect. In the light of these findings, the validity of Wahlstrand et al.'s main conclusions appears highly questionable. 
G\"unter Steinmeyer, Ayhan Demircan, Carsten Br\'ee
physics.optics