Abstract

The trivial way to drive phonons with a specific symmetry consists in the use of a two-pump-beam geometry. The associated set-up is well known as transient grating or four wave mixing experiment. The phonon wave-vector value q is there a function of θ angle value between the pump beams. The lowest value of q one can reach is obtained when θ=0. In the case of nonsymmetric modes this value depends on the anisotropy of the crystal under study. Nevertheless, all experimentally published works using one-pump-beam apparatus, lead to the excitation of completely symmetric modes: the processes involved had an isotropic polarization dependence[1].

© 1996 Optical Society of America