VO2 and W-doped VO2 thin films were prepared by Radio Frequency (RF) reactive magnetron sputtering using V-metal target. The amount of W doping was quantified by Rutherford Backscattering Spectrometry (RBS). The optical constants of VO2 and V1-xWxO2 films were inferred above and below the transition temperature by temperature-dependent multiangle ellipsometry in the Near InfraRed (NIR) spectral range and by temperature-dependent multiangle Fourier Transform InfraRed ellipsometry (FTIR) in the Near InfraRed Middle InfraRed (NIR MIR) spectral range up to 20,000 nm. The effect of the doping concentration on their optical constants was studied. A validation of the results was obtained comparing the optical constants determined by point-by-point fitting with those determined by the Lorentz Drude model and the empirical Lorentz Cauchy dispersion formula. (C) 2015 Elsevier Ltd. All rights reserved.