Plasmonic Saturable Absorbers

Plasmonic materials are able to spatially confine light to a nanometer scale far smaller than the diffraction limit, resulting in drastically enhanced electrical field strength and stimulating applications in nonlinear optics, energy, and biomedicine. Resonant excitation of plasmonic nanostructures by ultrafast pulses results in a subpicosecond‐scale transient photobleaching that originates from the thermalization and cooling of hot carriers, which manifests strong optical nonlinearity that is leveraged for optical modulation and switching. Herein, recent advances in the use of noble and non‐noble metal‐based plasmonic materials as saturable absorbers (SAs) in both solid‐state and fiber lasers for the generation of Q‐switched and mode‐locked pulses are discussed. Starting with a brief introduction on the operation mechanisms of pulsed lasers and photophysics of plasmonics, a discussion on the nonlinear optical (NLO) properties as well as the recent developments of pulsed lasers driven by these plasmonic SAs is focused upon. The pros and cons of using different plasmonic materials for SAs in terms of their material properties and linear/NLO responses are further analyzed. Along with a short summary of the current progress of plasmonic SAs, highlight future challenges in the development of plasmonic SAs for practical laser systems are finally highlighted.