A classical model for depolarization through decoherent superposition of dipoles **Co-hosted with CMIP**

Wednesday, April 15, 2015

12:00 pm | Physics 128

Presenter

Dr. Kurt Hingerl , Professor, Center for Surface and Nanoanalytics

**Co-hosted with Center for Metamaterials and Integrated Plasmonics (CMIP)**

A finite spectral resolution and/or an imperfectly collimated beam /and or an (areal) extended light source / and or an (areal) extended detector and/ or a sample with a varying thickness can produce depolarization in any polarization measurement. However, despite these experimental findings, there are to our knowledge no physical models published which trace the origin of depolarization back to the atomic properties. Therefore, in the talk I will explain crosspolarization - and subsequently depolarization by considering the common- not separable- effect between the light beam and the sample, described by coherence length and coherence area.

In optics we never measure the electric fields, because our available detectors are much too slow, but we measure their statistical second moments. So, for two classes of samples (and beams), for inhomogeneous ones, as well as for homogeneous with dimensions larger than the coherence length, a mathematical model for cross- polarization is presented. In inhomogeneous samples the Fresnel reflectances are not correct any more, these rely on homogeneity (i.e. arbitrary shifts of the sample along any surface direction). Cross- polarization then has to take into account radiating dipoles, whose radiation creates the scattered crosspolarized fields, still fully polarized, but after decoherent superposition, partially depolarized light results. In any structured sample there are inner boundaries present and it is straightforward to show that the usual boundary conditions on the continuity of the tangential electric field and the normal of the displacement field yield inherent contradictions at these inner boundaries. In homogeneous samples with dimensions larger than the coherence length, however, depolarization effects can only be observed if the light rays falling on the detector (for ellipsometry- the analyzer) travelled differences in distances larger than the coherence length.