Abstract

A long-wavelength lattice dynamic calculation applicable to crystals of any structural complexity and of any symmetry (that allows optical activity) reveals three mechanisms causing optical activity in crystals: first-order wave vector dispersion of the bonding forces; electric dipole-magnetic dipole interference; and electric dipole-electric quadrupole interference. Only the first mechanism has been found from lattice dynamics theories previously, while quantum mechanical derivations have produced only the second two. The first mechanism gives terms in the rotatory power proportional to ${\omega }^2/\left({\omega }_i^2-{\omega }^2\right)\left({\omega }_j^2-{\omega }^2\right)$, while the latter two give terms proportional to ${\omega }^2/\left({\omega }_i^2-{\omega }^2\right)$. Both types have been proved necessary to fit the frequency dispersion in particular crystals. Thus the present theory produces all the known mechanisms and needed dispersion from a single unified approach.

© 1988 Optical Society of America