Use of quadratic electroabsorption for measurement of the hyperpolarizability ss of asymmetric molecules

摘要

We show that quadratic electroabsorption (QEA) can be used for measurement of the hyperpolarizability beta in asymmetric, polar molecules. QEA has already been used to obtain the second hyperpolarizability gamma in centrosymmetric molecules. However, because of the existence of a static dipole moment mu in asymmetric molecules, beta can contribute significantly to the third-order susceptibility measured with the QEA experiment owing to a reorientational mechanism through the mixed term beta mu. We apply inhomogeneously broadened, quantum sum-over-states models for both beta and gamma to describe the QEA response of asymmetric molecules. Comparing the models and the data for two asymmetric nonlinear optical chromophores, we found that g yields the dominant response. QEA is thus a useful tool for measuring the dispersion of beta and can be used for reliable determination of the off-resonant value beta(0). (c) 2005 Optical Society of America.