Dispersion of χ(3) in polydiacetylene films from electroabsorption spectroscopy

Abstract Electroabsorption spectroscopy was carried out on a polydiacetylene, poly{[[8-butoxy carbonyl] methyl urethanyl]} 1-(5-pyrimidyl)-octa-1, 3-diyne (poly(BPOD)) film from 470 nm to 730 nm, and on a polydiacetylene poly-(butoxy-carbonylmethyleneurethane) (poly(4-BCMU)) film from 400 nm to 700 nm. The dispersion of the imaginary part of the complex χ eff (3) ′, which is a combination of χ 1133 (3) (ω;ω,0,0) and χ 3333 (3) (ω,ω,0,0), was directly determined from experiment. The real part of χ eff (3) ′ was calculated from its imaginary part by the Kramers-Kronig relation. The complex susceptibilities χ 1133 (3) (ω;ω,0,0) and χ 3333 (3) (ω;ω,0,0) were thus obtained from χ eff (3) ′ determined at normal and tilted incidence. The results for both polydiacetylene spin coated films satisfy χ 3333 (3) ≈ 1.5χ 1133 (3) , and are significantly different from the relation χ 3333 (3) = 3χ 1133 (3) , expected for an isotropic film. It indicates that the polymer chain segments in both polydiacetylene films lie mainly on the film plane instead of an isotropic distribution. The χ (3) values for both materials are of the order of 10 −11 esu. Some enhancement of nonlinearity of poly(BPOD) over poly(4-BCMU) is observed.

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