Crystal Surface Ablation And Optical Waveguides

Optical waveguides utilize the principle of total reflection of light at the interface of two media with different refractive indices.It can limit the light to a micro-structure with a micron dimension,as a result,achieving a high intra-cavity density and effectively integrating the optical circuit.Optical waveguides plays an important role in the fields of optical communication and integrated photonics.Optical crystals doped with rare earth ions are widely used in the preparation of optical waveguides.In particular,optical crystals doped with rare earth ions are widely used in the field of laser technology.Planar waveguides can be fabricated in optical crystal with ion-implantation,ion-implantation is a traditional method for optical waveguide.During this processes,ion implantation with a certain amount of energy into different materials causes the re-fractive index of the materials to change,thereby forming an optical waveguide structure.Femtosecond laser inscription,as a new type of optical waveguide preparation method,mainly focuses pulse laser with high peak power on the surface or inside of the material to cause non-linear effects and cause refractive index changes at the processing location and its surrounding area..In this thesis,we mainly use the femtosecond laser inscription and ion implantation technology to prepare microstructures and optical waveguide structures on the surface or inside of different optical crystals.The transmission,fluorescence,Raman,and other characteristics of waveguides are studied.The modification effect of femtosecond laser on the surface of calcium fluoride?CaF₂?crystal and its influence on the transmission characteristics of erbium-doped calcium fluoride?Pr:CaF₂?crystal optical waveguide structure and the characteristics of waveguide microregion luminescence properties and Raman spectrum were analyzed.In this thesis,optical waveguides are fabricated in yttrium-aluminum-garnet?YAG?bonding crystal?Nd:YAG/Cr:YAG?by the carbon ion beam implantation and their optical properties were studied.According to the prepared structures,the main work and results of this paper can be summarized as follows:The Femtosecond laser inscription is used to process the surface of the calcium fluoride crystal through two methods of stationary focusing and dynamic scanning.The microstructures?ablation holes and ablation lines?generated on the surface of calcium fluoride crystals under two processing methods are targeted.Curve fitting and analysis were performed on the size and processing parameters of the two microstructures,and finally the surface ablation threshold of the calcium fluoride crystal was obtained,and The results indicate that pulse accumulation effect and heat accumulation play significant roles in the process of surface ablation on crystals.Dual-line waveguides with low propagation losses and single-mode guidance in Pr:CaF₂ crystals are fabricated by applying femtosecond laser inscription.In contrast to the typical highly elliptic modes previously reported in dual-line waveguides,the guiding mode obtained in our work is highly-localized with a near-circular profile at wavelength of 633 nm.The investigations on confocal micro-photoluminescence and micro-Raman imaging enable us to illustrate the effect of different femtosecond laser filamentations on the localized refractive index change in Pr:CaF₂ crystals.In company with the mode simulation by finite element method,we further reconstruct the refractive index distribution of the fabricated waveguides.Our results indicate that highly-localized refractive-index increment caused by compressive stress between the lower parts of the filaments is the main mechanism for waveguiding,whereas the damage-induced refractive-index reductions at filaments and in the region between the upper parts of the filaments are responsible for the strong light confinement in both horizontal and vertical directions.A planar optical waveguide was prepared by ion implantation of heavy ions C³⁺ions into a Nd:YAG/Cr:YAG bonding crystal.By using a semiconductor laser with a wavelength of 633 nm,the transmission mode of the optical waveguide was measured based on the end-coupling method.The confocal micro-photoluminescence and micro-Raman imaging are investigated in order to further study the waveguide characteristics.