Relaxation of Polar Orientational Order in Nonlinear Optical Polymers by Second Harmonic Generation
Abstract
An investigation of the decay of the second harmonic generation (SHG) signals from a main chain accordion and a guest/host nonlinear optical (NLO) polymer has been carried out. The shape of the decay of the SHG signal from the main chain polymer is stretched exponential with the width parameter, B, increasing with increasing, temperature. The increase in B indicates a narrowing of the distribution of relaxation times. On the other hand, the SHG decay signal from the guest/host system is found to be better described by the sum of two single exponential functions with the first short time component affected strongly by the surface change effect and the second slow component associated with the relaxation of the macroscopic polarization. The time constant of the slow component is found to be successively increasing with the poling-decay cycle and it reaches a steady state value after several cycles. The relaxation time lengthening effect is obtained both above and below T(sub g); however, the effect rapidly diminishes as the temperature is increased above T(sub g). The temperature dependence of the steady state relaxation time is not Arrhenius; the Vogel-Fulcher-Tamann equation gives a satisfactory fit to the temperature dependence data.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 24, 1993
- Accession Number
- ADA269059
Entities
People
- C. H. Wang
- H. W. Guan
- S. H. Gu
Organizations
- University of Nebraska-Lincoln Department of Chemistry