Time-resolved hyper-Rayleigh scattering: Measuring first hyperpolarizabilities beta of fluorescent molecules

Time-resolved hyper-Rayleigh scattering experiments using a femtosecond mode-locked Ti-sapphire laser are presented. The technique is capable of discriminating between hyper-Rayleigh scattered light and fluorescent emission induced by multiphoton absorption with a time resolution of 80 ps. Measurements on the non-fluorescent organic molecules crystal violet and calix-[4]arene demonstrate that the technique can measure first hyperpolarizabilities beta consistent with experiments using a Q-switched Nd:YAG laser. The first hyperpolarizability beta of a fluorescent molecule, which is often overestimated when using a nanosecond laser system, can be corrected for long-term fluorescence using the time-resolved technique as is demonstrated for the octupolar molecule 1,3,5-tris[(4-pyridyl)ethynyl]benzene.