Attosecond In Situ Measurement and Recombination

Abstract

The spectral phase of high harmonic and attosecond pulses is typically shaped by the interaction of the recollision electron with the strong field in the continuum. However, the phase of the transition moment coupling bound and continuum states can be significant in shaping the emitted radiation. The measurement of transition moment phase shifts can reveal information about attosecond electron dynamics and structure. Here, I demonstrate that all-optical approaches to attosecond measurement, based on perturbing recollision with a weak infrared field, are sensitive to transition moment phase shifts arising from electronic structure and multielectron interaction using analytical theory, ab initio simulation, and experiment. The insensitivity of all-optical approaches to transition moment phase shifts arising from ionic structure is found to be a result of a first-order cancellation of the effect of the perturbing field on the recollision electron wave packet and the transition moment. Prior to these findings, it was widely believed that all-optical methods were insensitive to the transition moment phase. The insensitivity of all-optical measurement to both ionic structure and propagation effects will permit for the unambiguous isolation of electron structure and multielectron interaction in attosecond measurement. These results will allow any laboratory capable of generating attosecond pulses to perform measurements of the transition moment phase without an additional experimental apparatus, even at wavelengths where the single photoionization cross-section becomes small.