Characterization of THz radiation by collimated wavefront aperture raster scanning

We present measurements for characterization of the beam profile and polarization pattern of lens-coupled photoconductive antennas (PCAs) at THz frequencies using a setup with antennas at fixed positions and a movable aperture placed in between collimating THz lenses. The measured beam patterns for co-polar and cross-polar components reveal the expected Airy disc and quadrupole behavior, respectively. The temporal evolution of the polarization in the directions of maximum cross-polar component follows a single-cycle circle with opposite handedness at each side of the antennas line-ofsight (LOS). Results are consistent with those obtained with fiber-coupled movable antennas, while enjoying the simplicity of a free-space laser-PCA feed which does not require painstaking laser realignment for each beam direction measure.