Superbandwidth laser pulses in a dispersive medium: Oscillating beyond the Fourier spectrum with unexpected propagation features

Abstract

The concept of superbandwidth refers to the fact that a band-limited signal can exhibit, locally,an increase of its bandwidth, i.e., an effective bandwidth greater than that predicted by its Fouriertransform. In this work, we study the propagation of superbandwidth laser pulses in a dispersivemedium, characterized by the group velocity dispersion. In particular, two important results arisefrom the analysis of the instantaneous frequency of the pulse obtained through the Wigner functiondistribution: First, it can be observed local oscillations of the electric field which are beyondthe Fourier spectrum of the incoming pulse. Second, for a range of values of the pulse synthesisparameters, surprisingly, the dynamics of the instantaneous frequency within certain temporal regions,corresponds to that of a pulse propagating in a medium with a group velocity dispersion ofopposite sign. This phenomenon is intrinsic to the special characteristics of the pulse and not tothe dispersive properties of the medium.