Beam waist measurement for terahertz time-domain spectroscopy experiments

Classical masking aperture methods are found to be mostly inaccurate to determine the terahertz beam size in terahertz time-domain spectroscopy (TDS) experiments, owing to complex diffraction effects. Here, we present a simple and reliable method for measuring beam waists in terahertz TDS. It is based on the suecessive diffraction by an opaque disk followed by a small circular aperture.