An apparatus for birefringence and extinction angle distributions measurements in cone and plate geometry by polarization imaging method

摘要

A new apparatus for flow visualization based on Polarization Imaging Method (PIM) is developed. In this method, the polarization imaging camera, which is composed of a photonic crystal and CCD image sensor, is used to measure anisotropy of refractive index tensor. The photonic crystal placed in the front of CCD image sensor works as an assembly of analyzer plates for each of photo detectors of the image sensor, which provides four polarization components of image. By analysis of the polarization imaging data, the spatial distribution of birefringence and extinction angle can be obtained simultaneously. Since birefringence and extinction angle have strong relationship with stress and orientation angle due to Stress-Optical Rule (SOR), their distribution is appropriate to understand non-uniform flow. The advantage of the apparatus was examined by imaging flow of wormlike micellar solution in uniform and non-uniform shear flows. In the uniform shear rate geometry of cone and plate, we successfully obtained spatial distribution of birefringence and extinction angle of flow-induced structure of threadlike micelles.