Direct measurement of the Rayleigh scattering cross section in various gases

Using the laser-based technique of cavity ring-down spectroscopy extinction measurements have been performed in various gases straightforwardly resulting in cross sections for Rayleigh scattering. For Ar and N2 measurements are performed in the range 470-490 nm, while for CO2 cross sections are determined in the wider range 470-570 nm. In addition to these gases also for N2O, CH4, CO, and SF6 the scattering cross section is determined at 532 nm, a wavelength of importance for lidar applications and combustion laser diagnostics. In O2 the cross section at 532 nm is found to depend on pressure due to collision-induced light absorption. The obtained cross sections validate the cross sections for Rayleigh scattering as derived from refractive indices and depolarization ratios through Rayleigh's theory at the few %-level, although somewhat larger discrepancies are found for CO, N2O and CH4.