Nonlinear response decay mechanism

The mechanism of the decay of nonlinear response in PPNA remains unclear, however, decay has also been reported for other functionalized polymers. (1-4, 8-11) It should be noted that the observed decay is significantly less than that seen for doped polymers, where nearly complete relaxation takes place. Q6, 17) In... 

Although both SH transients in Fig. 5.21 fall to a minimum at about the same time, their form is quite different and qualitative comparisons are useful. The isotropic contribution, /pp(/), decays as a single exponential, in agreement with previous measurements of submonolayer thallium deposition on polycrystalline electrodes [54]. The solid line in Fig. 5.21 a is an exponential fit with r = 10.7 msec. The exponential form suggests that the deposition occurs by an absorption, rather than a nucleation, mechanism [154]. The transient anisotropic response is not as simple. In fact, the initial fall in /ps( ) in Fig. 5.21 b is not a simple decaying exponential. The differing time dependencies for the isotropic and anisotropic responses suggests that f, the bulk anisotropic susceptibility element which is the only common element, is not the main source of the nonlinear response in either case. 

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