We investigate the contribution of two-photon states to the third-order optical nonlinearity in four squaraine compounds. Our experimental results using third-harmonic spectral dispersion are compared to experimental results obtained by other researchers using quadratic electro-optic spectral dispersion and femtosecond excited state absorption measurements. Different relative contributions from high lying two-photon states are seen using different experimental techniques. We also relate these results to finite-field and sum-over states quantum chemical methods which indicate that there are multiple high-lying states that contribute to the third-order nonlinearity. For one of these dyes, we find that contributions from a mixture of isomers needs to be considered. For this latter dye, we compare our calculated transition moments and third harmonic dispersion curve using quantum mechanical methods with our results from third harmonic spectral dispersion and find substantial agreement between the experimental and theoretical results.

Date Published: 16 October 1998
PDF: 11 pages
Proc. SPIE 3473, Third-Order Nonlinear Optical Materials, (16 October 1998); doi: 10.1117/12.328177

Published in SPIE Proceedings Vol. 3473:
Third-Order Nonlinear Optical Materials
Mark G. Kuzyk, Editor(s)