Knowledge Bank

A three wave mixing spectrum may have resonances corresponding to Raman frequency differences (CARS) or to two-photon absorption. Interferences between the resonances are manifested as line shape changes. Absolute two photon absorptivities, very difficult to measure by direct methods, may be related to known Raman scattering cross sections by line shape studies. Adequate signals are obtained with cw lasers, and the excellent mode quality and stability help reduce artifacts which may distort the measured dispersion curve. Care is necessary to reduce scattered light to acceptable levels, and experimental details will be described. Four diphenylpolyenes from stilbene to diphenyloctatetraene will be discussed.