Birefringence Caused by the Presence of Permanent Dipoles and Its Possible Threat on the Accuracy of Traditional Surface Plasmon

摘要

In arriving at the more intuitive “scattering form” of the Fresnel equations, microscopic physical electric and magnetic dipoles were rigorously employed as the source of electromagnetic waves by Doyle et al. Motivated by such an ap-proach, the authors started to speculate how the incorporation of permanent dipoles might affect Brewster angle of a specific optical material. It is found that in the presence of permanent dipoles, not only is the Brewster angle dependent on the incident light power as well as the dipole orientation, but also that two conjugate incident light paths result in distinctively different refractions. Experiments on dipole-engineered polyvinylidene fluoride films show that by way of adding/reducing permanent dipole density and varying orientations, the aforementioned theoretical predictions can be evidenced unambiguously in the visible light range. Further, effective polarization density can be quantified from the above experiments subjected to different dipole engineering processes. As a result, the traditionally elliptic contour of a slanted two dimensional section of the refractive index ellipsoid now manifests symmetric open splittings at near the traditional incident angle. It implies that severe challenge to the accuracy of traditional surface plasmon resonance measurements may arise in the presence of permanent dipoles of various morphologies, such as in the forms of na-no-particles or membrane double layers.