Anomalous behavior of nonlinear refractive indexes of CO₂ and Xe in supercritical states

Abstract

Direct measurement of pressure dependent nonlinear refractive index of CO₂ and Xe in subcritical and supercritical states are reported. In the vicinity of the ridge (or the Widom line), corresponding to the maximum density fluctuations, the nonlinear refractive index reaches a maximum value (up to 4.8*10^-20m²/W in CO₂ and 3.5*10^-20m²/W in Xe). Anomalous behavior of the nonlinear refractive index in the vicinity of a ridge is caused by the cluster formation. That corresponds to the results of our theoretical assumption based on the modified Langevin theory.