Accurate measurement of the refractive index of CO2 , N2, HE, O2 and air at 10.57µ m and T=23°C

The refractive index of carbon-dioxide, nitrogen, helium, oxygen and air have been measured at 23 C temperature by means of a tunable CO2 laser at 10.57 lm and of a differential interferometric technique. As the gas refractive index depends on the pressure P as n = 1 + aPP, the pressure coefficients aP has been measured with 5e-3 accuracy.