Abstract

The role two-photon states play in the third-order optical response of organic systems has received much recent attention.¹ Third harmonic generation (THG) measurements are especially useful since they directly probe coherent electronic processes involving two- and three-photon resonances.²,³ Degenerate four-wave mixing (DWFM) and nonlinear transmission (NLT) are complementary techniques which are also sensitive to two-photon states, but may also contain contributions from incoherent excited-state processes. The advantage of the latter experiments is that they yield information on the third-order coefficient χ⁽³⁾(-ω;ω,ω,-ω) which is directly related to the nonlinear refractive index of interest for device applications. A direct comparison of DFWM and NLT results, when coherent electronic processes dominate, to χ⁽³⁾(-3ω;ω,ω,ω) determined by THG should yield useful information concerning the origin of the nonlinear optical response.

© 1995 Optical Society of America