Spatiotemporal transformations of ultrashort terahertz pulses

We have experimentally studied the propagation in free space and through fo cusing optics of subpicosecond half- and single-cycle terahertz pulses emit ted by large-aperture emitters. The spatial transformations of the beams ar e connected to phase changes and effective frequency filtering and lead to spectacular changes in the pulse time profile. The experimental results are in excellent agreement with the predictions of a simple analytical model b ased on a Gaussian-beam approximation. (C) 1999 Optical Society of America [S0740-3224(99)01210-2].