Semi- and Full Interpenetrating Polymer Networks as Stable Second-Order Nonlinear Optical Materials
Polymeric materials with second-order nonlinear optical (NLO) properties have been extensively studied for their potential applications in electro-optic modulation and frequency doubling devices.1,2 The second-order NLO properties in these polymer are present when the chromophores are aligned in a non-centrosymmetric manner. In order to be useful in practical devices, the alignment of NLO chromophores in the poled polymers must be sufficiently stable at temperatures above 100°C. Since the alignment of the chromophores resulting from poling is not in a state of thermodynamic equilibrium, the poled order would relax to a random configuration in an absence of electric field. In a prototypical guest/host system, Stähelin et al. demonstrated a fitting of the temporal relaxation to a Kohlrausch-Williams-Watts (KWW) equation establishing that the decay of the dipole alignment is explained by a single relaxation phenomenon.3 A fit of the relaxation times to the Williams- Landel-Ferry (WLF) equation pointed out that relaxation of the second order NLO properties is mainly related to the glass transition temperature (Tg) of the media. Thus NLO chromophores are usually incorporated in a polymer which has a high Tg in order to prevent the randomization of the poled (aligned) NLO molecules.
KeywordsInterpenetrate Polymer Network Second Harmonic Polyamic Acid Second Harmonic Intensity Increase Crosslinking Density
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