Attosecond Interferometry

In this chapter, we introduce all-optical attosecond interferometry using high-harmonic generation (HHG). Interferometry provides an access to phase information, enabling the reconstruction of ultrafast electron dynamics with attosecond precision. We discuss two main pathways—internal and external attosecond interferometry. In internal interferometry, the manipulation of quantum paths within the HHG mechanism enables phase-resolved studies of strong-field processes, such as field-induced tunneling. In external interferometry, the phase of the light emitted during the HHG process can be determined using optical interference in the extreme-ultraviolet regime. Both pathways have significantly progressed the state of the art of ultrafast spectroscopy, as evidenced by numerous examples described in this chapter. All-optical attosecond interferometry is applicable to a wide range of systems, such as atomic and molecular gases and condensed-matter systems. Combining the two pathways has the potential to access to hitherto elusive ultrafast multi-electron and chiral phenomena.