Real-time generalized terahertz time-domain ellipsometry enabled by dual-channel photoconductive antennas

Generalized ellipsometry can uncover the optical properties of anisotropic materials, in which the light–matter interaction alters the polarization state. In the terahertz frequency range, generalized ellipsometry has been infrequently realized due to the challenge of rapidly controlling and measuring THz polarization. Here, we report the development and calibration of a high-efficiency terahertz time-domain generalized ellipsometer based on two dual-channel photoconductive antennas. The fiber-coupled multi-pixel devices act as source and detector and achieve a high data throughput with four independent terahertz pulses in a single optical delay scan, without the need for any bulky or slow polarization elements such as polarizers. Following a one-off system calibration, an accurate optical characterization of a uniaxially birefringent Al2O3 crystal serves to validate the method. Our technique benefits from efficient data throughput, full polarization-resolved capability, and reduced system complexity, paving the way to in situ and real-time monitoring applications.