Pulsed focused fields

Abstract

Highly concentrated clumps of field energy that move through an environment without diffusing are of interest for a variety of applications. The basic problem is the synthesis of source distributions over an initial aperture to achieve this objective. Various analytical approaches have been used to explore how initial transient source field distributions can be tuned up so as to generate compact wavepackets that stay together indefinitely. The meaning of “staying together” and “indefinitely” depends strongly on how the problem is defined and has led to some startling conclusions in the early phases of investigation. At present, there seems to be agreement that no radically new phenomena are operative here but that interesting pulse shapes can be synthezied by clever spectral tuning of input conditions. Various techniques—based on direct time-domain synthesis, real and complex spectral synthesis, and use of transient beam-type basis elements—are reviewed within the context of causality and finite aperture size. Also discussed is a modeling scheme whereby a pulsed focused beam is generated analytically by assigning complex values to the source location and initiation time. This parametrization is useful for converting spherical pulse interaction with a perturbating environment directly into focused pulse interaction with that environment. [Work was supported by the Innovative Science and Technology Office through the U.S. Army Harry Diamond Laboratory.]