Jie Ren,Hongbo Xia,Yue Wu,Yaqun Han,Shufen Zhang,Suli Wu
Mie resonant structural colors have recently emerged as a promising approach for large-scale and high-precision material appearance design to replace plasmonic structures. However, Mie resonant structural colors are still limited in the gamut of red because high-order multipoles such as electric and magnetic quadrupoles (EQ, MQ) usually exist in blue band when the electric dipole (ED) and magnetic dipole (MD) located in red band. Here we achieved pure red Mie resonant structural color based on ZnO spheres. Both simulation and experimental results proved that the dipole resonance and quadrupole resonance can be separated effectively by decreasing the refractive index of the resonator. By comparing different materials, ZnO is the most suitable material to generate a pure red color. Further, by controlling the distance of ZnO spheres on the substrate, high-order multipole resonance was inhibited completely and pure red Mie resonant structural color was achieved. In addition, by tuning the size of ZnO spheres, bright purple, blue, green, yellow, orange, and red colors were also realized. Finally, complex patterns can be easily made by the spraying method. This work opens new perspectives on full-color Mie resonant structural colors.
Van der Waals (vdW) heterostructures offer a promising platform for optimizing and controlling physical properties of a variety of materials and devices, which has attracted extensive attentions in ultrafast photonic applications. Here, a hybrid vdW saturable absorber (SA) based on ZnO sphere heterostructures has been fabricated by transferring the low-temperature hydrothermal method ZnO spheres onto gold mirrors and covering with Au nanoparticles and the graphene layer. In comparison with the ZnO sphere SA, the vdW SA exhibits the stronger emission intensity in the ultraviolet-visible range and the higher optical absorption in the near-infrared range, respectively. Meanwhile, by using the balanced twin-detector technology, a modulation depth of 6.6% has been obtained from vdW SA, which is 2.8 times greater than that of the solo ZnO SA due to the harvest of photons and the transfer of photon-generated carriers in the vdW heterostructure. Based on the hybrid vdW SA, a quite stable Q-switched laser and a mode-locked laser operation with a tunable wavelength range from 1531.4 to 1560.4 nm have been achieved. These results demonstrate a effective strategy for enhancing nonlinear optical properties of SAs and pave a way for developing novel types of SAs for the application of ultrafast lasers.
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