Nontensorial Anisotropy of the Optical Field Effect at Thresholds and Saddle-Point Edges

Abstract

Previous treatments of the optical field effect at direct interband threshold (Franz-Keldysh effect) are generalized to saddle-point edges (Seraphin effect). The discussion demonstrates that nontensorial anisotropies are present in both cases. For practical reasons, however, it appears that nontensorial anisotropy should be easier to observe in the Seraphin effect than in the Franz-Keldysh effect. The anisotropy enables one to assign an edge to interband critical points located in specific regions in the Brillouin zone, and thus provides a powerful tool for solid-state spectroscopy. Strain and nonlinear effects are discussed briefly.