Development of a double-beam rheo-optical analyzer for full tensor measurement of optical anisotropy in complex fluid flow

Abstract.

The design and testing of the Double-Beam Rheo-Optical Analyzers, DB-ROA is described. The DB-ROA contains the two optically modulated laser beams that are transmitted through a sheared sample in different angles. The full components of the stress tensor can be evaluated simultaneously by a single measurement of the birefringence and orientation angle of each beam. The mechanical properties are also measured simultaneously with the optical properties. This system can be applied to both steady and transient shear flows. Three types of DB-ROAs are designed. They are distinguished by the optical modulation system, that is (1) a single modulator system, (2) a synchronization of two modulators, and (3) a two individual modulator system. The performance tests were carried out and its validity was demonstrated by comparison between the optical and the mechanical measurements of the first normal stress difference. The signal-to-noise ratio was strongly affected by the choice of the oblique angle of the second beam. The design features for the different optical modulation systems are discussed.