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We show that, when a spatially localised electric pulse is applied at theedge of a quantum spin Hall system, electron wavepackets of the helical statescan be photoexcited by purely intra-branch electrical transitions, withoutinvoking the bulk states or the magnetic Zeeman coupling. In particular, aslong as the electric pulse remains applied, the photoexcited densities losetheir character of right- and left-movers, whereas after the ending of thepulse they propagate in opposite directions without dispersion, i.e.maintaining their space profile unaltered. Notably we find that, while themomentum distribution of the photoexcited wave packets depends on thetemperature $T$ and the chemical potential $\mu$ of the initial equilibriumstate and displays a non-linear behavior on the amplitude of the applied pulse,in the mesoscopic regime the space profile of the wave packets is independentof $T$ and $\mu$. Instead, it depends purely on the applied electric pulse, ina linear manner, as a signature of the chiral anomaly characterising masslessDirac electrons. We also discuss how the photoexcited wave packets can betailored with the electric pulse parameters, for both low and finitefrequencies.

Photoexcitation of electron wave packets in quantum spin Hall edge states: effects of chiral anomaly from a localised electric pulse