Three-photon Absorption Process Research Articles

Anisotropy of Dye Diffusion in Smectic Phases Studied by Forced Rayleigh Scattering

Abstract We have observed strong thermal grating excitation in the isotropic and nematic phase of pentylcyanobiphenyl (5CB) in wave-mixing experiments using intense green picosecond excitation pulses at λ = 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.

The blue up-conversion luminescence of vitroceramics codoped with Tm 3+ and Yb 3+ ions pumped with 680 nm

A study of the spectroscopic properties of PbF 3+GeO 2+WO 3 vitroceramics doped with Tm 3+ and codoped with Yb 3+ and Tm 3+ ions upon 680 nm dye laser light excitation is made. The up-conversion emission and excitation spectra have been measured at room temperature. An enchancement of blue emission centered at 478 nm in the codoped sample is observed. We suggest that this result is due to the interaction between Yb 3+ and Tm 3+ ions. When the excitation power of 680 nm light is increased, a three-photon absorption process happens for another blue (451 nm) emission.

Theory of three-photon absorption

A general theoretical expression is derived for the probability of a three-photon absorption process. It is concluded that three-photon absorption to a discrete level may be observed if the radiation field contains a laser beam and additional light with a continuous frequency distribution and that a transition to a continuum ofstates may be observed if the radiation field consists of laser light only. The selection rules for three-photon absorption are basically the same as for one-photon absorption.