Measurement of high order Kerr refractive index of major air components

We measure the instantaneous electronic nonlinear refractive index of N-2, O-2, and Ar at room temperature for a 90 fs and 800 nm laser pulse. Measurements are calibrated by post-pulse molecular alignment through a polarization technique. At low intensity, quadratic coefficients n(2) are determined. At higher intensities, a strong negative contribution with a higher nonlinearity appears, which leads to an overall negative nonlinear Kerr refractive index in air above 26 TW/cm(2). (C) 2009 Optical Society of America