Calculation of the Index of Refraction of Neon and Argon*

We use the Kramers–Kronig dispersion relation to calculate the real part of the index of refraction of neon and argon for energies ranging from zero into the x-ray region. The cross sections of these gases are known experimentally to an accuracy of about 5%. We also use calculations of the oscillator strengths of the discrete transitions. We first correct the values of the cross sections to make them agree with the very accurate experimental value of the polarizability, and with the Thomas–Reiche–Kuhn sum rule.Our results for the index of refraction generally agree with existing theoretical calculations and experimental measurements to within 10%.