VUV radiometry below 100 nm: the high-power hydrogen arc as a standard source of continuum radiation between 53 nm and 92 nm

Abstract

A stationary hydrogen arc discharge may be used as a standard source of radiation in the VUV below 100 nm. The Lyman resonance continuum is used, the cross sections of which are theoretically well known. The method described is based on optically thin radiation, requiring high plasma temperatures and an effective helium gas separation in the arc. The investigations demonstrate that, in appropriate experimental conditions, the plasma is indeed transparent down to the onset of the He ground-state absorption. Above that, the VUV spectral radiance can be predicted within less than 15% uncertainty from conventional plasma diagnostics. For a first application, the He continuum has been measured between 65 nm and 92 nm. The consistency of these results with theoretical calculations confirms the validity of the concept presented.