Transmission ellipsometry studies of both nematic and smectic liquid crystals (LCs) confined by mixed conductor substrates are reported. By simultaneously measuring the Stokes parameters of transmitted light, we follow the modification of the polarization state of the monochromatic light propagating through the LC cells. The analysis of the polarization states of the probe beam during the application of a specific voltage waveform at the LC samples allows obtaining important physical information on the investigated systems. The weakening of the anchoring energy in nematic LC samples and the experimental evidence of the Goldstone mode during the switching process of smectic LCs are reported. (C) 2003 Elsevier B.V. All rights reserved.