Far-field diffraction of pulsed optical beams in dispersive media

Propagation of a pulsed optical beam (a train of ultrashort optical pulses) inside a linear dispersive medium is studied in the far field without maki ng the paraxial approximation. This approach permits us to obtain analytica l results that are valid for relatively large diffraction angles. Pulse cha racteristics are found to be affected considerably by the combination of di ffraction and dispersion. In a weakly dispersive medium, pulses wider than a few optical cycles maintain their shape but experience temporal and spect ral shifts whose magnitude depends on the diffraction angle. When the effec ts of group-velocity dispersion are included, the pulse width depends not o nly on the diffraction angle but also on the nature of dispersion (normal v ersus anomalous). Much larger off-axis pulse widths are predicted in the ca se of anomalous dispersion. (C) 1999 Elsevier Science B.V. All rights reser ved.