Abstract
The performances of two localized pulses that have lately attracted attention are compared. The first localized field, the focus wave modes, was recently shown to be causally launchable from flat apertures characterized by having time-dependent radii. It is demonstrated that the second localized field, the X waves, can be also be generated from finite-time dynamic sources. A comparison of the decay patterns of the two wave fields is carried out. It is emphasized that such carrier-free pulses with ultrawide bandwidths can perform differently, even if they are excited by use of apertures with the same dimensions and with initial illumination wave fields of comparable frequency bandwidths. The propagation characteristics of such localized pulsed fields in the near- and far-field regions are studied. Based on an understanding of the spectral depletion of such pulses, a method is suggested to slow the decay rate of the pulses in the far-field region.
© 1997 Optical Society of America
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