How is the UV spectroscopic ellipsometer better than a visible spectroscopic ellipsometer? A spectroscopic ellipsometer measures thin film thicknesses and indices of refraction by measuring phase difference (delta) and amplitude change (psi). It is plotted on a reflectance vs. wavelength graph, which is better than a single wavelength ellipsometer because the single wavelength ellipsometer only measures at one wavelength and can only measure the thickness of a single transparent layer and the refractive index of that wavelength, and a multiwavelength ellipsometer (spectroscopic ellipsometer) is more accurate because it measures at a spectrum of wavelengths and can be used for multilayer stacks and thin films. I believe that the UV spectroscopic ellipsometer is more accurate than the visible spectroscopic ellipsometer because of the properties of the material under UV light. Is this true? Why?