The traditional Ellipsometry is only valid in the domain of specular reflection on a plane and isotrope surface. Therefore ellipsometry is not well suited for the characterization of birefringent or depolarizing materials.
When depolarization occurs, the analysis of the polarization states might be done using Stokes formalism and Mueller matrices.
The optical response of a physical system to polarized light is described by the Mueller Matrix (4x4). In the particular case of an isotropic and specular surface, this matrix can be reduced to a 2x2 matrix with only two coefficients different from zero.
For the sake of being able to analyze more complex materials and surfaces, we have developed a Mueller Ellipsometer, capable of measuring the 16 Mueller coefficients. One of the originalities of the instrument, which makes him more attractive for the use of a non-specialist, is the calibration method which is made in just a few minutes and is independent of eventual non-linear responses of the optical elements of the instrument.
The first Mueller Ellipsometer worked under only one wavelength, but we have recently developed an instrument that works in the whole visible spectral range. Moreover, it has the advantage of a particularly simple conception: The polarization states generator (PSG) and analyzer (PSA) are identical and are composed by a polarizer, a wavelength film and two ferroelectric liquid crystals, oriented and piloted in an optimized way. A CCD camera is also included in order to separate all the spectral components at the same time.
Contact : Antonello De Martino - Enric Garcia-Caurel