Light bullets and supercontinuum spectrum during femtosecond pulse filamentation under conditions of anomalous group-velocity dispersion in fused silica

We report the results of theoretical and experimental research on spectrum transformation and spatiotemporal distribution of the femtosecond laser radiation intensity during filamentation in fused silica. The formation of light bullets with a high power density is first observed in a femtosecond laser pulse in the anomalous group velocity dispersion regime at a wavelength of 1800 nm. The minimum duration of the light bullet is about two oscillation cycles of the light field.