An optical measurement system for evaluating a reference sample, having at least a partially known composition, includes a reference ellipsometer and at least one non-contact optical measurement device. The ellipsometer includes a light generator, an analyzer, and a detector. The light generator generates a beam of quasi-monochromatic light of known wavelength and polarization, which is directed at a non-normal angle of incidence relative to the reference sample. The analyzer creates interference between S and P polarized components in the beam after interaction with the sample. The detector then measures the intensity of the beam, which a processor uses to determine the polarization state of the beam and, subsequently, an optical property of the reference sample. The processor then can calibrate an optical measurement device by comparing a measured optical parameter from the optical measurement device to the determined optical property from the reference ellipsometer.