Analysis of the diffracted field near the focal region due to the birefringence of the field flattening lens of the laser scanning system

In most cases of molding with glass or optical polymers, the birefringence caused by the internal mechanical stresses remaining in the molding material is inevitably avoided. The distribution of the residual stress can be annealed through slow cooling, but is disadvantageous in terms of shape accuracy and manufacturing time. In this study, an analytical model is suggested for calculating the diffracted field near the focal plane by considering two primary meaningful parameters: the difference in the orientation angle between the fast axis and the slow axis and the path difference between the two axes. To verify the reliability of the analytical model, the experimental spot profile from the image forming lens of the laser scanning unit with a specific degree of birefringence was compared with the analytical result. Also, based on the validated optical analysis model, the optical performance in the near-focus region was analyzed considering the variation of the orientation angle deviation and the phase delay difference between the two axes.