Third harmonic generation spectrum of a degenerate ground state conjugated polymer. Direct evidence of simultaneous two- and three-photon resonance
✍ Scribed by J. McElvain; M. Cha; H. Yu; N. Zhang; F. Wudl; A.J. Heeger
- Publisher
- Elsevier Science
- Year
- 1995
- Tongue
- English
- Weight
- 395 KB
- Volume
- 247
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
We report the third harmonic generation (THG) spectrum of poly(dioctyldipropargylmalonate) (PDDPM), covering pump energies from 0.6 to 1.4 eV. Like trans-polyacetylene, PDDPM has a bond-alternated structure and a twofold degenerate ground state. The phase of the nonlinear optical susceptibility, X(3)(3to), undergoes a 2~r shift, demonstrating that two nearly simultaneous resonances (at 0.7 and 0.9 eV) are traversed, as expected for degenerate ground state polymers where the two-photon mid-gap state formed by neutral soliton-antisoliton pairs plays a dominant role in X °) processes.
Exceptionally high values have been reported for the third order nonlinear optical (NLO) susceptibility, X(3)(-3o9; to, oJ, o9)-X(3)(3o9), of the transisomer of polyacetylene, trans-(CH), . Equally important, the large NLO response was found to be symmetry specific; the corresponding X(3)(3o9) val-