Investigation On Characterization Of Micro-and Nano-structures Induced By Femtosecond Laser In Alkali Oxide Glasses

In the 2010s,the development of information technology,and the increasing demand for information processing and broadband network lead to more demand of the information communication technology.As the Si-based semiconductor technology is approaching the theoretical limit,photon or photoelectron are used as the information carrier in the integrated optical circuit,which will raise the possibility of evolution on information technology in future.One of the most important problem in the development of integrated optical technology is the fabrication of various optical functional micro-and nano-structures in transparent materials,such as glass,with high efficiency.And femtosecond laser machining is frequently used in functional micro-and nano-structures formation inside transparent materials,which may accelerate the development of integrated optical circuits.In this thesis,we studied the phenomenon and characterization of micro-and nano-structures induced by femtosecond laser.A series of oxide glasses with alkali cations were prepared,and several kinds of micro-and nano-structures were induced inside the glass substrates,whose properties and formation mechanisms were discussed.The results and important conclusions are shown as below.1.We induced the micro bubble structures inside sodium germanate glass using high repetition rate femtosecond laser.The morphology,size and space distribution of the micro bubbles were investigated.We studied the formation and properties of the micro bubble structures,and suggest that the formation of bubbles is caused by the distortions of the light field around the focal region as laser is focused by a high-aperture lens through an interface with refractive index mismatch.And the influence of laser parameters as well as optical field distribution on the position of micro bubbles were also investigated.We studied the directional migration of the micro bubble structures,which may be attributed to the flow of glass melt around laser irradiation area.These space-selective micro bubble structures can be applied in optical components,such as micro optical switches and microcavity lasers.2.Using low repetition rate femtosecond laser irradiation,we induced nanograting structures inside germanate glasses doped with a series content of alkali cations.We analyzed the dependence of the size and morphology of the nanograting structures on the femtosecond laser irradiation and laser parameters.We suggest that the interaction between defects and linear/nonlinear absorption of the femtosecond laser pulse energy by the glass play important roles for the formation of the nanograting structure.We observed a unique long period nanograting structure inside glass sample using the femtosecond laser.The morphology and birefringence signal intensity of nanograting structures were characterized,which were deeply affected by the content of alkali cations.The nanograting structures can be applied in high density optical storage and integrated optical circuit.3.We studied the element redistribution behavior around the laser irradiated region of germanate glasses and tellurate glasses after high and low repetition rate femtosecond laser irradiation.In alkali germanate glass,we observed the influence of laser repetition rate on the element distribution as well as glass network structure in the femtosecond laser irradiated area.The element diffusion under low laser repetition rate was also been observed.In lanthanum ion doped tellurate glasses,we observed little element distribution in tellurite glass,while the glass density changed significantly.We believe that the low viscosity nature of tellurate glass play an important role in the formation of the abnormal element diffusion.Based on the femtosecond laser induced element redistribution,we can obtain the spatial control of the micro-optical properties inside glass,which is very promising for the preparation of optical components,such as optical waveguide.