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

Abstract The spectral radiance Lλ (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). Lλ (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