Electrical and optical properties such as power absorption, index of refraction, and complex conductivity of polyacetylene film are determined by transmission measurement using a source of freely propagating subpicosecond pulses of THz electromagnetic radiation and without invoking the Kramers-Kronig relationships. Four types of polyacetylene samples, undoped pristine, FeCl4- doped pristine, undoped and stretched twice, and FeCl4- doped and stretched twice, are compared experimentally. The undoped pristine polyacetylene is found to have a resonance of 2.45 THz. The stretched polyacetylene have an angle-dependent curve along the direction of the polarized THz beam. (C) 2004 Elsevier B.V. All rights reserved.