Metallic Photonic Structures And Ultrafast Plasmons

Metallic photonic nanostructures exhibit more exceptional and richer optical properties,as compared with their dielectric counterparts,because of the excitation of surface plasmons.They have been applied extensively in surface-enhanced Raman scattering(SERS)spectroscopy,biosensors,lasers,waveguides,and optoelectronic devices.High-efficiency,low-cost,and large-area fabrication methods are important for the physical studies and applications of metallic photonic structures.Meanwhile,surface plasmon resonance not only induces local-field enhancement,but also possesses ultrashort lifetimes,showing excellent performance in the applications in ultrafast alloptical switching devices.This thesis focuses its studies on the performances and ultrafast processes in metallic photonic structures in the following three aspects:(1)Development of lowcost,high-efficiency,and large-area fabrication techniques for metallic nanostructures,supplying new approaches for the photophysical studies and the design of plasmonic photonic devices.(2)Ultrafast photophysics in the coupling between photonic and hybrid plasmonic resonance modes in a three-dimensional(3D)metallic grating for exploring ultrafast optical switching devices.(3)Ultrafast photophysics and design of multipolar plasmonic devices based on metallic hemispherical nanoshell arrays,supplying new physics and techniques for all-optical switching systems.This thesis mainly includes the following works:1.We start with a brief review on the current progress in the field of metallic photonic structures,as well as their applications in a variety of research areas.We discussed in a major part the ultrafast photophysical processes in plasmonic nanostructures and their applications in optical switching devices.Meanwhile,we summarize the fabrication techniques for metallic photonic structures.Considering the restrictions by the currently available fabrication techniques,we developed some new methods with the advantages of low costs,high efficiency,and large-area structures.(1)For laser interference ablation,we studied the heat transfer processes during the direct writing of photonic structures into gold films.(2)Using optical fibers to deliver the laser beams,we introduced a direct writing method defined as flexible interference ablation.(3)Making use of photoreduction process,we developed a new method for the fabrication of large-area metallic photonic structures based on the photoreduction of silver ions by ultraviolet laser beams.We also studied the related physics and influencing factors that are involved in the above fabrication processes.These economical and efficient fabrication methods laid basis for the photophysical studies and application of the metallic photonic structures.2.We studied the narrow-band spectroscopic response performance of a 3D grating consisting of metallic nanowires.We discovered a strong Fano coupling process between the Rayleigh anomaly and the hybrid plasmon resonance.Using femtosecond pump-probe,we studied the ultrafast dynamics of the coupled resonance mode and revealed that a red-shift of the resonance spectrum under the strong excitation by femtosecond pump pulses.On this basis,we achieved optical switching process with an efficiency as high as 22.4%.3.We studied the multipolar plasmonic resonance modes and the related ultrafast photophysical processes in metallic hemispherical nanoshell structures,which constituted the basic mechanisms for the ultrafast optical switching effects.Using steady-state spectroscopy,we first studied the spectroscopic response of the unidirectional multipolar plasmons in metallic nanoshell arrays and verified the simultaneous dipolar and hexapolar plasmons in a single device.Femtosecond pumpprobe experiments revealed different dynamics for these two kind of plasmons,where a redshift and a broadening process was induced for the dipolar and hexapolar plasmons,respectively,by the excitation of the pump pulses.We achieve a 270-fs optical switching deivce with a modulation efficiency of 25% by the dipolar plasmon.