Spatiotemporal focusing of single-cycle light pulses

We investigate experimentally and numerically the properties of single-cycle terahertz pulses propagating through a focus. The experimental data clearly show changes in pulse shape resulting from the Gouy phase shift and apparent superluminal pulse propagation. The pulses are also considerably distorted by diffraction effects. A solution of the time-domain diffraction integral is necessary to explain the details of the data and leads to an excellent agreement between experiment and theory.