Multi-Photon Excitation and Relaxation of Thermal Gratings in the Nematic Liquid Crystal 5CB

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Abstract
We have observed strong thermal grating excitation in the isotropic and nematic phase of pentyl-cyanobiphenyl (5CB) in wave-mixing experiments using intense green picosecond excitation pulses at δexc = 532 nm. It is shown that optical heating is provided by a three-photon absorption process in the commonly called “highly transparent” liquid crystal. We have further investigated the relaxation of the induced thermal gratings, which exhibits a critical slowing at the nematic-isotropic phase transition.