Spatiotemporal separation of high harmonic radiation into two quantum pathcomponents

We present a spatiotemporal analysis of high harmonic generation, showing e vidence for the presence of several quantum path contributions to the atomi c dipole moment. We show that the harmonic radiation can largely be describ ed as a sum of two fields having a phase proportional to the intensity of t he generating field. We compare our results to recent experimental results demonstrating this separation [M. Bellini et al., Phys. Rev. Lett. 81, 297 (1998)]. We show how the temporal and spatial coherence properties are infl uenced by this effect, and discuss how it could be used to obtain better co ntrol of the generated harmonic radiation. [S1050-2947(99)00402-3].