ABSTRACT
A number of liquids or liquid solutions exhibit the optical effect of streaming birefringence, i.e., these liquids become birefringent under the action of shear forces in a flow. Light propagation in such a medium is directionally dependent. An incident light wave separates in the birefringent liquid into two linearly polarized components whose planes of polarization are perpendicular to one another, and which propagate at different phase velocities. Birefringence can be generated in fluids consisting of elongated and deformable molecules or having elongated, solid, crystal-like particles in. Flow visualization by streaming birefringence depends on the behavior of the fluid’s refractive index; optical interference is the principal technique for visualization. For quantitative evaluation there must be a relationship between the observable refractive index field and the state of the flow, a so-called flow—optic relation. The oldest and most widely used technique for visualizing the flow of a birefringent liquid is an apparatus called a polariscope, which is also used for photoelastic experiments.
