We have designed a hyper-Rayleigh scattering scheme to measure six scalar invariants of the squared hyperpolarizability tensor β2. Our theoretical approach expresses the rotational invariants of the irreducible β components as scalars, which eliminates the need for difficult frame transformations. We applied our scheme to several conjugated chiral molecules and found that there are significant Kleinman-disallowed pseudotensor contributions to their hyperpolarizability. These components, along with a large optical rotation and the results of quantum-chemical calculations, indicate a handed nonplanar delocalization of the charge-transfer system in such molecules as predicted by quantum-chemical calculations and are expected to lead to macroscopic second-harmonic generation in axially aligned polymer materials. Pseudotensor contributions to the hyperpolarizability in chiral molecules were found to be as large as the vector contribution in p-nitroaniline. We qualitatively investigated the dispersion in the Kleinman-disallowed components and confirmed that these components are smaller at longer wavelengths.
© 1998 Optical Society of America
[Optical Society of America ]
S. F. Hubbard, R. G. Petschek, K. D. Singer, N. DSidocky, C. Hudson, L. C. Chien, C. C. Henderson, and P. A. Cahill, "Measurements of Kleinman-disallowed hyperpolarizability in conjugated chiral molecules," J. Opt. Soc. Am. B 15, 289-301 (1998)