On the Use of a Low Current Argon Arc with a MgF2-Window as a VUV-Transfer Standard of the Spectral Radiance (125nm≦λ≦335nm)

Abstract

The spectral radiance L_λ (λ) of a low current argon arc (current: 10 A, power requirement: ≦1.5 kW, pressure: 1.2 bar, gas: A) has been calibrated with a relative uncertainty of 5% in the wavelength range between 125 nm and 335 nm by means of the electron synchrotron radiation of DESY (Hamburg, Germany). L_λ (λ) exceeds generally the spectral radiance of the carbon arc and the commercially available deuterium lamps by more than one order of magnitude. A significant reduction of the transmittance τ(λ) of the MgF₂-window, inserted for the sealing of the arc chamber has been observed in the entire wavelength range when the low current argon arc has been flanged to a vuv-optical system. The behaviour of the transmission factor of the MgF₂-window under the influence of increasing times of exposure to arc radiation has been investigated as a function of wavelength. The reduction of the transmission factor of the MgF₂-window in the uv (λ > 185 nm) is nearly negligible ( < 2 % over an operating time of 30 hours) when the arc has been utilized without a connection to a vuv-optical system