The Voigt-type microwave kerr effect in semiconductors with spherical constant energy surfaces

Abstract

This chapter discusses the theory of linear elastic wave propagation in crystals. Three different linear elastic waves may propagate along any given direction in an anisotropic material. These three waves are usually not pure modes as each wave has particle displacement components both parallel and perpendicular to the wave normal. When one of these components is normally much larger than the other, the wave with a large parallel component is called quasilongitudinal, while the wave with a large perpendicular component is called quasitransverse. In the event that sufficient symmetry prevails such that the direction of propagation is elastically isotropic or if the material is elastically isotropic, then all modes become pure modes. For linear elastic wave propagation in crystals, the direction of the flow of energy per unit time per unit area, the energy-flux vector, does not in general coincide with the wave normal as it does in the isotropic case. An expression for the energy-flux vector can be obtained by considering the time rate of change of the total elastic energy contained in the wave field. Measurement of the linear elastic properties of solid materials is one of the most important applications of ultrasonic techniques. The measurements range from determination of second-order elastic constants, which yield fundamental information about the binding forces among atoms in crystals, to the field of nondestructive testing where macroscopic internal defects are located in structural solids.