Abstract

The importance of the anisotropy of the nonlinear optical susceptibility tensors of materials has been recognized since the earliest investigations of the interaction of intense laser radiation with matter. The role of anisotropy has been particularly relevant in the design of electro-optic and frequency doubling devices, where the anisotropy of the second-order susceptibility is used to optimize the effective electro-optic or second harmonic coefficient and that of the first-order susceptibility is the key to phase-matching. By comparison, little experimental attention has been paid to the anisotropy of the third- order susceptibilities and almost none to the crystal orientation dependence of the two- photon absorption (TPA) coefficient β To date, in cubic materials, reports of the TPA anisotropy have been limited to single beam measurements using linearly polarized beams, which were dominated by carrier accumulation and did not allow independent determination of all the susceptibility tensor elements.¹ The dearth of information on the anisotropy of TPA is surprising since TPA has been studied extensively in semiconductors and other crystalline materials, in part, because of its role in initiating laser damage, because of its possible use as an optical limiting mechanism, because it is a limiting factor to the achievable switching energy in a given material, and because the nonlinear refraction on which many switches rely is itself closely related to the dispersion in the TPA coefficient.

© 1993 Optical Society of America