Bimetallic PtNi Octahedral Alloy Nanoparticles as Broadband Nonlinear Optical Modulators for Ultrafast Photonics

Metallic nanomaterials serve as compact integrated modulators in ultrafast multiwavelength photonics. Engineered bimetallic alloy nanoparticles exhibit enhanced and tunable optical properties that surpass those of single-component systems by alloying. Here, bimetallic PtNi octahedral alloy nanoparticles are demonstrated as a promising material platform for ultrafast multiwavelength lasers, exhibiting exceptional nonlinear optical responses across the entire near-infrared spectrum. Q-switched laser operations were successfully achieved at 1028.5, 1561.2, and 1911.2 nm, utilizing PtNi octahedral alloy nanoparticles. Furthermore, utilizing the four-wave mixing effect induced by PtNi alloys, simultaneous five-wavelength lasers were realized with channel spacings of 1.7 and 2.2 nm in the 1- and 2-µm bands, respectively. It is found that PtNi alloys are comparable nonlinear optical modulators with other typical nanomaterials in ultrafast multiwavelength photonics. Moreover, first-principles calculations reveal that substantial 3D states of the Ni concentrated near the Fermi level are the major cause of the enhanced optical absorption, where the surface Ni plays an important role. This work establishes a novel paradigm for developing advanced material platforms for nonlinear optical modulation, paving the way toward breakthroughs in ultrafast multiwavelength photonic systems.