 Ellipsometry

Ellipsometry measures the change in polarization of an electromagnetic wave upon specular reflection to infer material properties. For a simple planar sample, the complex reflection-coefficient ratio is written $\rho =r_p/r_s=\tan \Psi e^{i\Delta }$: $\Psi$ describes a relative amplitude and $\Delta$ a relative wave phase between the two incident polarizations.

A source, polarization-control optics, sample at a known incidence angle and analyzer with a photodetector form a basic instrument. Repeating measurements across wavelength and angle constrains refractive index and film thickness through a model of the layered sample. The fitted thickness is not read directly from $\Psi$: roughness, layer structure and correlated model parameters can produce ambiguous fits.

Ellipsometry is an optical technique used to measure the thickness and optical properties of thin films. It is based on the principle of polarized light and how its polarization state changes upon reflection from a sample surface. The technique is particularly sensitive to changes in film thickness, material composition, and refractive index, making it valuable in various fields, including materials science, semiconductor fabrication, and nanotechnology.