ossila.com, but you may experience issues browsing our website. Please consider upgrading to a modern browser for better security and an improved browsing experience.An ellipsometer measures the change in the polarization state of light after it interacts with a sample. Ellipsometry is an optical technique that can be used to measure the thickness and optical properties of thin films. It can also be used to determine sample properties (including roughness and extinction/absorbance coefficients) at each wavelength of interest.Changes in the polarization state can be quantified by measuring the amplitude change and the phase shift induced by interaction with a sample. These changes in the polarization state of light can be exploited to study film thickness values that are significantly smaller than the wavelength of the incident light. Ellipsometers can obtain sub-nanometer resolution using visible wavelengths, thus beating the diffraction limit.When we refer to the polarization state of light, we are referring to the direction in which the electric field is oscillating. In naturally occurring light (sunlight, etc), this orientation is random - but in polarized light sources, this orientation is controlled.During reflection from a surface, polarized light can be resolved into two components: one which is parallel (p-polarization) and one which is normal to the plane of incidence (s-polarization). Here, we define the plane of incidence as the plane containing both the beam path and the surface normal.If the p- and s-components are out of phase by another arbitrary amount, or their amplitudes are completely different, then the light is elliptically polarized. This is the general state of polarization and it is where ellipsometry gets its name. We are measuring changes in the ellipticity of the polarisation state using an ellipsometer.When a linearly polarized light beam is reflected from a thin film sample, its polarization state will change. This is caused by differences in the reflection coefficients for p and s components at each interface that the light encounters. It is also affected by small phase shifts in the two components as the light traverses the medium comprising the film. These changes in polarization can be characterized by the difference in polarization amplitude (ψ) and phase (Δ) between the s-polarized and p-polarized light. The changes in polarization state, caused by interaction with the film, will change the lights state of elliptical polarisation (or ellipticity).For light with a given elliptical polarization, reflection from and interaction with the film can cancel out the phase changes in the incident light and result in linearly polarized light upon reflection from the sample. This is the working principle that underpins how nulling ellipsometers work. A linear polariser is used to extinguish the linearly polarised light that is reflected from the sample under these conditions. This is achieved by crossing the polariser axis with the direction of polarisation of the linearly polarised reflected light to create a null signal. If you know of the polarisation state of incident and reflected light, you can find the ellipsometric angles ψ and Δ. A suitable model can then be used to extract the thickness and optical properties of the sample being studied.Nulling ellipsometry is one type of ellipsometry technique. Another approach uses rotating polarisers (or other rotating optical elements) to directly measure the ellipticity of the light reflected from a sample. Alternatively, active optical elements such as acousto-optic modulators can be used to apply periodic variations to the polarisation state of light. Both of these measurements are dynamic in nature. They are typically faster measurements than those obtained from a nulling instrument but tend to be less accurate.An ellipsometer begins by directing the light source through a polarizer, creating linearly polarized light. This light is then passed through other optical components to control the incident light’s ellipticity. This creates a beam with a well-defined polarization state. The components needed to control ellipticity depends on many things including the ellipsometer light source and the desired application of the ellipsometer.This elliptically polarized light then interacts with the sample, usually a thin film or several thin films supported on a substrate. As polarized light interacts with each layer, its polarization state will change.The reflected light is then passed through a second polarizer (called the analyzer), before this signal is detected with a detector. These measurements can be taken at multiple angles of incidence to enable more accurate measurement of the amplitude difference and phase shifts at each incident wavelength.