Anisotropy of the nonlinear optical susceptibility ?(3) in polydiacetylene single crystals

Abstract

The anisotropy ofχ(3) in Poly-bis(p-Toluene Sulfonate) of 2.4-hexadiyne-1.6-diol (PTS) PolyDiAcetylene (PDA) single crystals is investigated by Degenerate Four-Wave Mixing (DFWM) at a wavelength of 720 nm. The symmetries ofχ(3)(−ω;ω, −ω,ω) identify the non-vanishing and independent components of the tensor. For the calculation of the χ(3) elements from the measured values, the anisotropy of both the linear optical index of refraction and the absorption coefficient is included in the coupled wave approach. A magnitude of 10−10 esu is measured for theχ(3) component if all beam polarizations are parallel to the polymer chains. The least upper bound for all other measurable components is estimated to be 10−12 esu. The results for the intensity dependence of the DFWM signal are explained in terms of a thermooptic effect. Measurements on the orientational dependence of the DFWM signal in the samples are carried out, and the influence of the anisotropy of the linear optical parameters on the measured curves is discussed. A method for the preparation of thin layered polymer single crystals of poly-bis (4-ButoxyCarbonyle-Methylene-Urethane) of 4.6-decadiyne-1.1-diol (4-BCMU) and the first DFWM measurements on these samples are presented.