Accurate measurement of the refractive index of CO2, N2, He, O2, and air at 10.57 μ 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 μm and of a differential interferometric technique. As the gas refractive index depends on the pressure P as n = 1 + αPP, the pressure coefficients αP has been measured with 5e–3 accuracy.