Manipulation of quantum paths for space–time characterization of attosecond pulses

Abstract

An all-optical method to measure the space–time characteristics of an isolated attosecond pulse, without temporal and spatial averaging, is now demonstrated. The approach will provide further insight into the generation of ultrafast light, and may possibly be used to finely control the pulse characteristics. Attosecond extreme-ultraviolet pulses1 have a complex space–time structure2. However, at present, there is no method to observe this intricate detail; all measurements of the duration of attosecond pulses are, to some extent, spatially averaged1,3,4,5. A technique for determining the full space–time structure would enable a detailed study of the highly nonlinear processes that generate these pulses as a function of intensity without averaging6,7. Here, we introduce and demonstrate an all-optical method to measure the space–time characteristics of an isolated attosecond pulse. Our measurements show that intensity-dependent phase and quantum-path interference both play a key role in determining the pulse structure. In the generating medium, the attosecond pulse is strongly modulated in space and time. Propagation modifies but does not erase this modulation. Quantum-path interference of the single-atom response, previously obscured by spatial and temporal averaging, may enable measuring the laser-field-driven ion dynamics with sub-cycle resolution.