Patent US 7,903,264

Wavelength dispersion of intensity of light reflected from an evaluation object is measured. A complex refractive index of a substance forming the evaluation object and the environment are prepared. Virtual component ratios comprising a mixture ratio of the substances forming the evaluation object and the environment are prepared. Reflectance wavelength dispersions to the virtual component ratios are calculated. Similar reflectance wavelength dispersions having a small difference with the measured wavelength dispersion are extracted from the reflectance wavelength dispersions. Weighted average to the virtual component ratios used for calculating the similar reflectance wavelength dispersions are calculated to obtain a component ratio of the substance forming the evaluation object and the environment so that weighting is larger when the difference is smaller. A structure of the evaluation object is determined from the calculated component ratio.