Propagation of half-cycle far infrared pulses

We have studied the propagation of half-cycle (i.e., unipolar) electromagnetic pulses centered at terahertz frequencies, in free space, through apertures, and through focusing optics. The temporal pulse shape of an apertured half-cycle pulse is significantly altered during propagation, but retains much of its unipolar character after traveling more than 20 times the aperture dimension. When focused by an achromatic lens, a half-cycle pulse evolves into a single-cycle pulse at the focal waist and an inverted half-cycle pulse in the far field. (C) 1997 Optical Society of America.