Conclusion
In terms of power series expansion, we calculated the nonlinear after-effect and response function from the general time-evolution equation. From the result, we theoretically elucidated the connection between TEB and FEB. Also we clarified that the dc component of the electric birefringence relaxation yielded the information similar to that from the dielectric relaxation. We confirmed that our theoretical treatment agreed with the experimental results of NaPSS by two-dimensional electric birefringence relaxation spectroscopy. Further, we measured the FEB spectrum of conducting polymer solution. As a result, we detected the rod-coil transition directly by the FEB method. In addition, we clarified the two kinds of intra-molecular carrier transport mechanisms, that is, the carrier diffusion within the contour length and the diffusion within the more local range between the defects.