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25 September 1989 Growth And Nonlinear Optical Properties Of Single Crystal Films Of Polydiacetylenes
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Polydiacetylenes, a class of organic polymers are important because of large nonresonant |χ(3)| I and sub-picosecond response times. The nonresonant domain of these materials covers the wavelength from ~0.8 μ to ~2.0 μ which is a desirable spectral window from the standpoint of telecommunication applications. The magnitude of χ(3) in this wavelength range is ~10-9 esu which is the largest nonresonant value known for any material. The absorption spectrum of these materials consists of a sharp excitonic peak at ~2 eV (α~106 cm-1) followed by weak interband transitions at ~2.4 eV. The excitonic state has been shown to be a combination of Frenkel and charge-transfer states. Thus these excitons are unlike the excitons that are usually observed in inorganic semiconductors and seldom dissociate into free carriers (as evidenced by poor photoconductivity throughout the absorption range). Consequently the relaxation time of the excited state of these systems has been found to be as low as ~1.8 ps. Away from the resonance the response is instantaneous even at ~0.3 ps time scale. These are some of the unique characteristics that make polydiacetylenes attractive for many future applications in all-optical signal processing. In this paper we will discuss the crystal growth, our present understanding of the origin of nonlinearity and waveguiding aspects of these materials.
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M. Thakur, D. M. Krol, B. I. Greene, G. C. Chi, and K. O'Brien "Growth And Nonlinear Optical Properties Of Single Crystal Films Of Polydiacetylenes", Proc. SPIE 1104, Growth, Characterization, and Applications of Laser Host and Nonlinear Crystals, (25 September 1989);


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