Ion Beam Synthesized Metallic Nanoparticles:Tailoring Of Optical Properties And Photonic Applications

Due to the unique localized surface plasmon resonance effects,metal nanoparticles have a wide range of applications and broad development prospects in information storage,medical detection,biosensors,and integrated circuits.Since Feynman first proposed nanotechnology in the 1960s,the research of metal nanoparticles in the field of photonics has ushered in vigorous development.Among them,the linear and nonlinear optical modulation of dielectric materials by local surface plasmon resonance effect has become one of the research hotspots in the field of integrated photonics.However,traditional metal nanoparticle synthesis technologies,such as chemical methods,have complex processes and high costs.In addition,the synthesized nanoparticles are easily affected by the environment and not conducive to the development of integration.Therefore,the realization of stable and controllable preparation and industrial production of metal nanoparticles is of great significance for the research of new nanocomposites and the development of multifunctional integrated photonic devices.In recent years,ion beam technology has shown great potential application in the fabrication of metal nanoparticles and the modification of dielectric materials.By accelerating the metal ions and irradiating the surface of the dielectric material,energy transfers from metal ions to the target material.Due to the limitation of the solid solubility of the material,the implanted metal ions are supersaturated to precipitate out,thereby synthesizing metal nanoparticles inside the dielectric material.Different from the traditional metal nanoparticle synthesis methods,ion beam technology brings new prospects for the optical property modulation of dielectric materials by metal nanoparticles.On the one hand,the interaction between nanoparticles and dielectric materials leads to the unique optical properties,and the optical response can be further adjusted by changing the injection conditions to control the physical properties such as the size and spatial distribution of the nanoparticles;on the other hand,the nanoparticles are embedded in the dielectric materials.They are protected by dielectric materials and have high stability.In theory,any kind of metal nanoparticles can be synthesized in any material.At the same time,ion beam technology,as one of the mature micro-nano processing technologies,is the foundation and key to achieving highly integrated and industrialized photonic devices.So far,people have successfully used ion beam technology to synthesize different kinds of metal nanoparticles in dielectrics such as glass.However,current research at home and abroad is mainly limited to the formation of metal nanoparticles in amorphous dielectric materials,and there are few related studies on the fabrication of metal nanoparticles for optical property modulation of dielectric crystal materials and their application.As an important optical medium,multifunctional dielectric crystal materials(such as Nd:YAG,Nd:YCOB,BGO,CaF2,etc.)have properties such as frequency conversion,nonlinear absorption and refraction,and are widely used in scientific research,industrial production,and daily life.They play an irreplaceable role in various areas.Realizing the synthesis of metal nanoparticles in dielectric crystal materials,clarifying the formation mechanism of metal nanoparticles in dielectric crystal materials,modifying multifunctional dielectric crystal materials by metal nanoparticles,and combining three-dimensional micro-nano structures for integrated photonics device of particles and dielectric crystal composite materials,it is not only of important theoretical significance,but also has broad application prospects,opening a new path for the development of multifunctional integrated photonics.The main contents of this thesis include the synthesis of metal nanoparticles in different dielectric materials using ion implantation technology;the use of swift heavy ion irradiation technology to tailor the optical properties of metal nanoparticles;designing optical waveguide structures by ion implantation,femtosecond laser writing and other micro-nano processing technologies;and combining metal nanoparticles with optical waveguide structures to achieve Q-switched mode-locked ultrafast laser generation.According to the purpose of the experiment and the types of dielectric materials selected,the main work of this paper can be summarized as follows:We report on the fabrication of spherical silver nanoparticles in fused silica(SiO2)by low-energy silver ion implantation.According to the linear absorption spectrum,it is proved that the nanoparticles own excellent local surface plasmon resonance effect.The absorption peak is located at 400 nm,and has red-shift with the increase of the fluence.Based on the Z-scan experiment,the third-order nonlinear absorption at 515 nm shows superior saturation absorption with nonlinear absorption coefficient of-64.6 cm/GW,and the third-order nonlinear refraction exhibits obvious self-focusing phenomenon with nonlinear refraction index of 4.2×10-12 cm2/W.At 1030 nm,the nanoparticles show the weak saturable absorption.Low-energy silver ion implantation technology is used to fabricate spherical silver nanoparticles in neodymium-doped yttrium aluminum garnet(Nd:YAG)crystals.The absorption spectrum shows that the surface plasmon resonance absorption peak is located at 500 nm with a red-shifted when the fluence increases.The third-order nonlinear absorption results show that the nanoparticles could enhance the substrate's saturable absorption by six orders of magnitude at 515 nm,and the third-order nonlinear refractive index is also enhanced by four orders of magnitude compared with that of Nd:YAG crystals.At the 1030 nm band,the nanoparticle exhibits obvious saturable absorption with a modulation depth of 0.8%.Low-energy silver ion implantation is used to fabricate spherical silver nanoparticles in bismuth germanate(BGO)crystals.The entire implantation region is polycrystalline due to damage during ion implantation,making the experimental absorption peak at 466 nm has a blue shift compared with the simulated value.The third-order nonlinear absorption results show that,after the nanoparticles are introduced,the two-photon absorption effect of the BGO crystal transforms to three-photon absorption due to the modulation of the surface plasmon resonance.We propose a two-layer structure model to explain the asymmetric Z-scan results in this process.Using swift xenon(Xe)ion irradiation technology,the spherical silver nanoparticles in Nd:YAG crystals are elongated,and the surface plasmon resonance response of the nanoparticles is tailored.According to the polarized absorption spectrum,the surface plasmon resonance response of the un-irradiated spherical nanoparticles is independent of polarization,and the absorption peak is 448 nm at both 0° and 90° polarization.For the surface plasmon resonance response of the elongated nanoparticles,the absorption peak has a red-shift to 452 nm at 0°polarization and blue-shift to 443 nm at 90° polarization.We construct a nanoparticle elongation model and analyze the effects of nanoparticle aspect ratio and size on polarization-dependent surface plasmon resonance response.Considered with the near-field distribution of nanoparticles,the enhancement of fluorescence of Nd:YAG crystal by nanoparticles is explained,which breaks the traditional view that ion-implanted nanoparticles will lead to the fluorescence quenching of the substrate.Using swift heavy ion irradiation technology with C60 clusters and Xe ions,spherical gold nanoparticles are elongated in different substrates(SiO2,indium tin oxide crystals,calcium fluoride crystals).The matrix dependence is investigated during the nanoparticle elongation process.The experimental results show that the weakest anti-sputtering ability of calcium fluoride crystals leads to the destruction of nanoparticles,and the amorphous SiO2 has the strongest anti-sputtering ability,and nanoparticles have the best elongation effect in indium tin oxide crystals.Compared with the 200 MeV Xe ion irradiation,4 MeV C60 cluster has similar elongation effect,but the sputtering ability is stronger.It is the first time to realize nanoparticle elongation in a crystalline material by fast heavy ion irradiation with the crystalline state of the matrix material maintained.At the same time,C60 cluster irradiation can reduce the energy required for the nanoparticle elongation by 98%.We report on the fabrication of cladding optical waveguide in neodymium-doped calcium fluoride(Nd:CaF2)crystal.The effects of pulse energy,optical waveguide depth and waveguide size on the waveguiding performance are explored.The end-face coupling system shows that the optical waveguide is independent to the polarization of incident light,with a minimum transmission loss of 0.7 dB/cm.The optimal femtosecond laser processing parameters are demonstrated to own pulse energy of 0.17 ?J,depth of 3.0 ?m,and diameter of 50 ?m.At the same time,the fluorescence results show that the fluorescence performance in the waveguide region is not affected by laser writing processing and is completely retained,which provides a theoretical basis for the generation of cladding waveguide lasers.Low-energy silver ion irradiation combined with femtosecond laser processing technology is used to fabricate silver nanoparticles and cladding optical waveguide structures on SiO2 and Nd:YVO4 crystals,respectively.We firstly propose a two-dimensional nanoparticle array model to simulate the unique plasmon resonance absorption peak caused by the interaction between non-isolated nanoparticles.The red shift of the absorption peak is used to enhance the nonlinear optical response at near infrared band.The temperature analysis during the Z-scan process through the two-temperature model proves that the nanoparticles have saturable absorption at the near infrared band.Using silver nanoparticles in SiO2 as a saturable absorber,combined with the cladding optical waveguide in Nd:YVO4,Q-switched mode-locked laser generation at 1-micron band is achieved.The laser threshold is 31.5 mW,the maximum output power is 245 mW.the slope efficiency is 29.3%,the maximum repetition frequency is 6.5 GHz,and the minimum pulse width is 27 ps.Using carbon ion implantation combined with precision diamond blade cutting technology,ridge optical waveguide is fabricated in the neodymium-doped calcium yttrium borate(Nd:YCOB)crystal.The polarization dependence of the optical waveguide is completely preserved with the maximum output power of 56 ?W,and the fluorescence intensity in the waveguide region is also improved.In addition,compared with the planar optical waveguide,the frequency doubling efficiency of the ridge optical waveguide is increased by 66%.and the output power of the maximum frequency doubling signal is increased by 10.7%.Using low-energy silver ion irradiation,oxygen ion implantation,and precision diamond knife cutting technology.ridge optical waveguide with integrated silver nanoparticles is fabricated on Nd:YAG crystal.The nanoparticles are embedded in the upper surface of the optical waveguide at a depth of 53 nm,and the average particle diameter is 3 nm.The end-face coupling result shows that the optical waveguide has superior polarization dependence.After the nanoparticles are integrated,the reverse saturable absorption of the optical waveguide is converted into excellent saturation absorption.Under the pump of 810 nm laser,we successfully realized the generation of Q-switched mode-locked laser at 1064 nm on the integrated optical waveguide device using the evanescent field coupling effect.The maximum laser repetition frequency is 10.53 GHz and the minimum pulse width is 29.5 ps.