ABSOLUTE CALIBRATION OF A VACUUM CZERNY-TURNER SPECTROMETER IN THE RANGE 1200-7000-ANGSTROM

The vacuum Czerny-Turner high-resolution spectrometer observing the plasma of the reversed-field-pinch device RFX has been absolutely calibrated in the spectral range 1215-7000 Å, in order to measure the emission spectrum in absolute units, with particular reference to the heliumlike carbon and oxygen ion lines. The source used to calibrate the spectrometer in the vacuum and near-ultraviolet region is a deuterium lamp; its spectral radiance was determined by comparison with the synchrotron radiation of the electron storage ring BESSY, in Berlin. A typical error of 35% has been estimated. In the visible a standard tungsten lamp has been used. The calibration has been transferred to an ultragrazing incidence XUV spectrometer by means of the branching-ratio technique, using the intensity ratio between the intercombination 1s2 1S-1s2p 3P0 and the 1s2s 3S-1s2p 3P0 transitions of carbon, nitrogen, and oxygen heliumlike ions.