Newly designed organic/inorganic film for optical second-harmonic generation
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Newly designed organic/inorganic film for optical second-harmonic generation Tomokatsu Hayakawa, Dai Imaizumi, and Masayuki Nogami Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Aichi 466-8555, Japan (Received 7 June 1999; accepted 17 November 1999)
In this paper we report the fabrication of organic/inorganic film for optical secondharmonic generation by a sol-gel method for the purpose of the improvement of thermal stability and chemical resistance. The film contains the azo dye Disperse Orange 3 protected by poly(vinylpyrrolidone) in a reticulation of silica gel, whose structure was developed by the spinodal decomposition and the gel-forming process as temperature increased. Corona-poling at elevated temperature could successively induce the optical second-harmonic nonlinearities. The dependence of temperature and field strength on the second-harmonic intensity was also investigated.
I. INTRODUCTION
It has been recognized that many organic molecules exhibit large optical nonlinearities due to the delocalization of their -electronic clouds, which have drawn considerable interest as potential candidates for applications in electrooptic and photonic devices such as optical switches, light modulators, and logic gate devices.1–3 Because of the third-rank tensorial nature of the secondorder nonlinear coefficient, the bulk medium that contains these molecules also must have polar symmetry for effects arising from the molecular contribution to be useful; this places new constraints on the molecularengineering approach.4 Organic crystals have not found widespread use in integrated optics and waveguide optics or as bulk components for the parametric process, mainly because of the difficulty of growing large, high-quality single crystals with the required processability, mechanical integrity, and ambient stability. Alternative approaches have been proposed: one method is to deposit a noncentrosymmetric multilayer film consisting of layers of dye-substituted polymers interleaved with inert organic molecules by the Langmuir– Blodgett technique.5,6 Another method is to deposit a film consisting of randomly oriented guest nonlinear dye molecules in a host polymer, which are then orientationally ordered by raising the temperature at which molecular motion is greatly enhanced, applying an external aligning field, and then cooling before the field is removed.7–9 The nonlinear optical (NLO) effects of interest are a strong function of the magnitude of the orientational polarization, and the competition with thermal randomization effect must be overcome. To restrict molecular motion, modified approaches to some extent have been attempted to incorporate the nonlinear chro530
J. Mater. Res., Vol. 15, No. 2, Feb 2000
mophores in a host that can be poled at lower temperature and subsequently crosslinked to effectively provide a polymer with high glass-rubber transition temperature. The polymers can be crosslinked either by thermal
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