Wave-packet recollision and pulse-shape effects in high-harmonic generation

Abstract
The recollision model of harmonic generation in a time-varying field has two elements: the emission due to a recolliding wave packet, and the quasiperiodic emission of wave packets in successive cycles. By discussing these issues separately, we explain the origin of blueshifting, and the ``smearing'' of the harmonic spectrum. We find that such a model shares many of the qualitative features of the semiclassical theories of harmonic generation.