Thickness-induced shifts in interband transition thresholds and ultrafast electron dynamics in gold films

In recent years, the study of ultrafast electron dynamics within metals has garnered widespread attention. Specifically, the interband transition threshold (ITT) in metal films, a key determinant of material optical properties, is crucial for understanding and designing new photonic materials and devices. This study investigates the effect of metal film thickness on ITT and its underlying mechanisms using transient reflection spectroscopy. It was found that ITT showed a redshift trend as the thickness of gold film decreased to less than 60 nm, a phenomenon attributed to the combined effects of strong electron-electron interactions and surface interface effects. This reveals how film thickness can regulate interband transition behavior in metals, thereby influencing their optoelectronic properties. These findings not only enhance our understanding of the electronic structure and optical properties of metal films but also provide a theoretical and experimental basis for the development of new nanophotonic devices.