Time-frequency analysis of light-bullet dynamics during femtosecond filamentation in the anomalous dispersion regime

Abstract

In this paper, we investigate the light-bullet dynamics during femtosecond laser filamenation in an anomalous dispersion regime based on the experimentally observed blueshifted resonant radiation (RR) in fused silica. A numerical simulation is performed and well reproduces the pronounced asymmetric feature of the RR spectra. By applying a time-frequency analysis to the propagating laser field, this specific spectral feature is found to be closely connected to the positively chirped property of RR in the time domain. In the context of the effective three-wave mixing model, this temporal chirp character of the RR is ascribed to the variable phase-matching conditions, which can be traced back to the accelerative propagation of the light bullet during its formation. Our work provides a deep understanding of the spatiotemporal dynamics of femtosecond laser-pulse propagation in condensed media.