A rotating-compensator multichannel ellipsometer has been developed for ultraviolet-extended real time operation over the spectral range from 1.5 to 6.5 eV The enhancements to the conventional rotating-compensator multichannel instrument to obtain this wide range include: (i) a tandem D-2-Xe source, (ii) MgF2 optical elements, (iii) a grating spectrograph blazed at 250 nm and (iv) two stages of order sorting filters internal to the spectrograph. The key in this effort is to maintain a flat spectral distribution over as wide a spectral range as possible in order to reduce spectrograph stray light, which is the primary error that limits the range of multichannel instruments. In this paper, new calibration and data reduction methods are described that determine the polarizer and analyzer angular offsets, and the rotating-compensator azimuthal phase angle and retardance spectra with the highest possible accuracy while minimizing instrument-related errors. (C) 2003 Elsevier B.V. All rights reserved.