Interaction of Optical and Infrared Radiation with Metastable Hydrogen Atoms

This paper is an extension of a previous one and discusses the theory of the quenching of the metastable $2S$ state of atomic hydrogen by means of optical radiation, for example by the light from a ruby laser. The case discussed is that for which the incident intensity is sufficiently weak for the usual quantum-electrodynamical perturbation theory to be valid. A procedure developed by Schwartz and others is used to carry out the sum over intermediate states without explicit enumeration. The results are given for a range of incident wavelengths from 5000 Å to 5μ. For unpolarized light from a ruby laser (6934 Å), the total cross section for quenching is found to be ${\sigma }_Q=1.27\mathrm{}\times {10}^{-22\mathrm{}}$ ${\mathrm{cm}}^2$. The cross section for coherent scattering has also been calculated for the same range of wavelengths; for ruby laser light, the total cross section for scattering is found to be ${\sigma }_S=1.03\mathrm{}\times {10}^{-23\mathrm{}}$ ${\mathrm{cm}}^2$.