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Beam-Profiling and Wavefront-Sensing of THz Pulses at the Focus of a Substrate-Lens

We report combined wavefront detection and beam profiling of single-cycle terahertz (THz) pulses. In our system, the electric field is recorded highly resolved in two spatial and one temporal dimension before and after propagation through an optical component. Using this approach, we examine the imaging properties of a hyperhemispherical silicon lens as it is commonly used in THz dipole antennas. We observe an asymmetric spatiotemporal field dynamic in the focus, which can be attributed to distortion of the incident wavefront in combination with the image properties of the lens. Diffraction on the lens aperture influences the spectral beam profile at the focus. The frequency dependence of the Airy pattern indicates a rapidly degrading Strehl ratio with increasing frequency.