Effect of the carbon dioxide concentration on the Refractive Index of air in a long gauge block interferometer

Abstract

In our previous work, four environment parameters including temperature, pressure, relative humidity and carbon dioxide concentration in a long gauge block interferometer chamber were measured continuously for 24 h. The refractive index of air in the chamber depending on three measured parameters was determined using the updated Edlén equation by assuming that CO2 concentration is constant at 450 ppm. In this study, the carbon dioxide concentration term was added into the updated Edlén equation and four environment parameters including temperature, pressure, relative humidity and CO2 concentration were measured continuously for 12 h. To characterize the influence of the carbon dioxide concentration on the refractive index of air in a long gauge block interferometer chamber, the refractive index of the chamber contents was determined using updated Edlén equations with constant and with variable carbon dioxide concentration terms. The results showed that the refractive index values obtained from the updated Edlén equations with constant and variable CO2 concentration terms were equal to 1.000268244 and 1.000268261, respectively.