Abstract

The picosecond photoconductivity of highly oriented polymer stretched transpolyacetylene was measured in the one-dimensional configuration (applied electric field parallel to the polymer chain) with respect to the polarization of the incident above- and below-gap excitations. The abovegap excitation was produced by 0.532 mm (2.4 eV), 25 ps pulses from a frequency-doubled YAG laser. For below-gap photoexcitation the fundamental frequency of the YAG at 1.06 mm (1.17 eV) was used. In each case the picosecond photoconductive response was maximum when the polarization of the incident optical pulse was perpendicular to the polymer chain. The anisotropy ratio (defined as the ratio of the photocurrent with perpendicular excitation to that with parallel excitation) for below-gap excitation was approximately 2.4 and was independent of intensity. The anisotropy for both excitations was normalized with respect to the number of absorbed photons. The above-gap anisotropy varied from 7.4 to 4.5 with respect to increasing intensity; and the photocurrent was greatest for below-gap excitation, independent of the optical field polarization. These results are accounted for in the soliton/polaron model.

© 1990 Optical Society of America