Characterization of Mueller matrices in retroreflexellipsometry

Ellipsometry is a widely-used technique for characterizing materials and thin films. The principle is based on the polarization changes after light is reflected or transmitted at a sample. In general, the shape of the sample should be flat or nearly flat because ellipsometry is sensitive to the angle of incidence, tilt angle and the sample position (height variation). For nonplanar surfaces, retroreflexellipsometry was proposed to solve the problem of the alignment. Despite of the Mueller matrix, the coherency matrix is often used for depolarization and noise reduction. In retroreflex ellipsometry, the measured Mueller matrix can be seen as a dual-rotation transformation. Therefore, it is important to discuss the changes of reference frames for Mueller matrices. In this report, the polarization model of retroreflex ellipsometry will be introduced. Decompositions and invariant quantities of a Mueller matrix with a dual-rotation transformation will be discussed.