Helium purge flow prevention of atmospheric contamination of cryogenically cooled optics on orbiting infrared telescopes

The ability of a He purge gas to protect the cryogenically cooled optics of orbiting infrared telescopes from the primary atmospheric contaminant, atomic oxygen, can be estimated by calculations simulating the He-O scattering events that would occur in the operating telescope. This paper reports results of accurate quantum mechanical calculations of the He-O differential cross sections sigma(theta, E) needed in such calculations. To facilitate the use of these cross sections, a simple separable function of E and theta is also given which provides an adequate representation of sigma(theta, E) for the entire range of relative collision energies studied, E = 0.02-1.66 eV.