Measurement of the nonlinear refractive index of air constituents at mid-infrared wavelengths

We measure the nonlinear refractive index coefficients in N$_2$, O$_2$ and Ar from visible through mid-infrared wavelengths (\lambda = 0.4 - 2.4 {\mu}m). The wavelengths investigated correspond to transparency windows in the atmosphere. Good agreement is found with theoretical models of $\chi^{(3)}$. Our results are essential for accurately simulating the propagation of ultrashort mid-IR pulses in the atmosphere.