Simulation and analysis of birefringence in magneto-optical discs .B. Numerical and experimental results

Physical insight into the complicated birefringence generation process during manufacturing of polycarbonate substrates for MO discs is presented using experimental as well as numerical results based on the model presented in Part A of this series. The decoupled approach for the computation of the flow-induced birefringence as proposed by Baaijens is shown to be in good agreement with numerical and experimental results of Flaman for the more viscoelastic polystyrene. The berefringence generation process in typical MO substrates is discussed in detail using numerical and experimental results. It is shown that not the flow-induced, but the cooling induced entropy-elastic stresses, i.e., the cooling-induced molecular orientation, dominates the vertical birefringence. The main contributions to the in-plane birefringence, on the other hand, will be seen to come from both the flow- and the cooling-induced stresses. The usefulness of the model presented in Part A is also demonstrated by comparing numerical and experimental results for various parameter variations, such as the mold temperature, the cooling time, and the variation of the mold clamping pressure. The numerical predictions are in good qualitative agreement with experimental data. However, for an improved quantitative prediction, a better knowledge of the shift-factor seems to be necessary.