Nonlinear optics as a probe of chiral ordering in amorphous semiconductors

Recent polytope models of amorphous semiconductors imply that the continuous random network has a preferred local chirality, that is, a preferred sign of the dihedral angle, extending over clusters of many atoms. The present work suggests an experimental test of this proposal. Symmetry arguments lead to two possible types of experiments: one involving local optical activity, and the other involving three-wave mixing. We present a detailed analysis of the latter: we show that a sensible definition exists for a local three-wave-mixing response of a single bond, develop a formalism for computing this local response within a tight-binding model, and perform computations that show that within a particular frequency regime (two high input frequencies above resonance and an output difference frequency below resonance) an experimentally detectable signal due to local chirality should be present. © 1988 The American Physical Society.