Optical properties and applications of metal nanomaterials in ultrafast photonics: a review

Metal nanomaterials have emerged as compelling candidates for ultrafast photonics applications, owing to their outstanding saturable absorption properties induced by surface plasmon resonance effects. In recent years, the exploration of saturable absorbers has encompassed noble to non-noble metals as well as diverse structures such as clusters, nanowires and nanoplates. Herein, we comprehensively elucidate the operational principles of metal nanomaterials in ultrafast lasers, including the surface plasmon resonance effect and their complex optical properties. Furthermore, recent advancements in metal nanomaterials utilized in ultrafast lasers have been systematically summarized and classified according to the dimensional structure that profoundly affects their properties. Moreover, the operating parameters of saturable absorbers based on metal nanomaterials are listed in detail. Finally, we look ahead to further directions of metal nanomaterials in ultrafast photonics, presenting explorations in metasurfaces, potential alternatives, and novel integration methods.