Theory and applications of attosecond transient absorption spectroscopy: From atoms to solids

Abstract This review comprehensively explores the theory and applications of attosecond transient absorption spectroscopy (ATAS) in studying ultrafast electronic dynamics across various systems, from atoms to solids. Driven by significant advancements in ultrafast laser technology, such as generating isolated attosecond pulses, ATAS enables detailed investigations of ultrafast electronic processes with unprecedented time resolution. The article introduces the fundamental principles and historical development of ATAS. Applications of ATAS are discussed in three main domains: in atoms, where it has been used to study build-up dynamics of Autler–Townes splitting, Fano resonance, light-induced states, etc.; in molecules, where it has revealed coherent molecular wavepacket dynamics and non-adiabatic dynamics near conical intersections; and in solids, where it has been extended to investigate ultrafast charge carrier dynamics in metals, semiconductors, and insulators. The review highlights the potential of ATAS in developing ultrafast optical switches and petahertz electronics. The ability of ATAS to probe and manipulate electronic dynamics at the attosecond timescale provides a powerful tool for exploring the fundamental limits of electronic and optical processes in materials.