Temporal Stability of Second-Order Optical Nonlinearity of Polyurethane: Influence of Poling Conditions

Poling-condition dependence of second-order optical nonlinearity of a polyurethane sample has been studied by the second-harmonic generation (SHG) method. Not only the magnitude of an SHG coefficient ( d 31 ) but also the temporal stability of d 31 depended on the poling conditions. The dependence of the temporal stability was weaker than that of the magnitude. The poling temperature ( T pol ) affected the stability more than the poling voltage, the poling time and the preheating time. The T pol leading to the best temporal stability agreed approximately with that leading to the highest d 31 . The dependence of the temporal stability is discussed from the viewpoint of molecular dynamics.