Principle and analysis for ellipsometers usable in the vacuum ultraviolet (VUV) region up to about 25 eV, which are consisting of a sample mirror and an inclined photodiode, are described. Our ellipsometer has two degrees of freedom in rotation; the main chamber can rotate around the axis of incidence and, the analyzer unit can also rotate around the axis of reflection. All the unknown parameters (Stokes parameters of the source, ellipsometric parameters of the sample and the polarization sensitivity of the inclined detector) are obtained by rotating the main chamber and analyzer independently and solving the simultaneous equations with the measurands. Measurement results on polarization characteristics of photodiodes, Stokes parameters of the beam emerging from a synchrotron radiation beamline, and optical constants of AlN film are given. It is concluded that the ellipsometer is advantageous in the simplicity and worked as intended. (C) 2014 Elsevier B.V. All rights reserved.