When light scatters from a turbid medium (a liquid with many fine suspended particles) it gradually loses its polarization at a rate which depends on the number of scatterings, the details of the medium and the type of polarization. Because almost all particles are unable to re-radiate photons in the same plane the incident light was polarized in, the scattered light forms interesting dipole-shaped patterns.
In the apparatus that was created, HeNe laser light is scattered by the medium, and the scattered light is focused into a CCD camera. The polarization of the incoming light and the orientation of an analyzer directly in front of the camera are adjusted to create several individual images which can be manipulated to form the 16 elements of a Mueller matrix. A Mueller matrix is a 4x4 matrix that describes the optical properties of a medium or device with respect to not only linear polarized light, but to circular or elliptical polarized light as well. Using images as the matrix elements instead of single values allows every point in the medium to be represented. With the help of false coloring, the 16 distinct Mueller matrix images look strikingly different and can be used as a ``fingerprint'' of the scattering medium for identification and comparison. Creating the setup involved in part carefully characterizing the polarization optics, and selecting and testing a suitable CCD camera.
Mueller matrix images obtained from a dilute
sample of 0.2 um diameter latex spheres show the characteristic
multi-lobed dipole patterns that laws of scattering predict.
Repeating the procedure using a sample of one half the concentration
of the initial mixture produced a decidedly different set of 16 matrix
elements. Graphed comparisons of intensity values in a selected
element clearly indicate how the Mueller matrix for a latex sphere
solution is altered with respect to concentration.
[Title Page]
[Summary]
[Introduction]