Poly third-order harmonic generation

Poly(3-alkyl-a-thiophene) systems show significant third-order nonlinear susceptibilities ( ) Though, oligothiophenes have been studied for their third-order susceptibilities, accurate third-order optical nonlinearity data obtained by degenerate four-wave mixing or electric-field-induced second harmonic generation (EFISH) are difficult to attain reliably on samples with poor solubility characteristics (92MM1901). 

Laser lights with short wavelengths are important in optical data processing, and conjugated polymers are expected to be useful materials for their generation. Optical third-harmonic generation measurements have been performed for poly(phenylacetylenes) " The magnitudes of the third-order susceptibility were 7 x 10 esu for poly(phenylacetylene) and in the order of 10 -10" esu for its derivatives . ... 

Abstract The anisotropic third-order nonlinear optical susceptibility of monodomain samples of nematic solutions of poly[l,4-phenylene-2,6-benzobisthiazole], PBT, a rodlike polymer, have been studied by third harmonic generation. Corresponding measurements have also been made for isotropic solutions of PBT. A substantial off-diagonal component of X( H-3co o),co,co) is measured, resulting in the generation of an elliptically polarized third harmonic signal for a fundamental linearly polarized along the director. 

The symmetry of the polymer and sidechains for materials such as poly(di-n-hexylsilane) dictate that is identically zero for these polymers. However, recent publications have described measurements of for poly silanes to be on the order of 10" - 10 12 esu for third harmonic generation [28] and four wave mixing processes [29], Two-photon absoiption cross section, being proportional to Imx ), should therefore be strong as well for this class of polymers. We have observed this to be the case, with x(3)=3.2x10 esu at 560 nm, and the primary excitation decay paths of energy transfer, polymer chain scission, and UV fluorescence very similar to those observed with single photon exposure [21,30]. 

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