Research On Local Regulation And Application Of Photo-thermo-refractive Glass Undergoing Ultrafast Laser Irradiation

The nonlinear effects in the interaction between ultrafast laser and transparent materials endow powerful function of space selective modification of materials,which makes three-dimensional micro-nano manufacturing technology based on ultrafast laser advance rapidly towards industrialization.Photo-thermo-refractive(PTR)glass is the most commonly used substrate material for fabricating high-efficiency volume Bragg gratings and other optical diffraction elements,and owns many advantages such as excellent optical properties,high physical and chemical stability and large refractive index modulation.However,the traditional exposure method of a UV laser double-beam interference based on the linear photo-thermal properties of PTR glass seriously restricts the development of its miniaturized and integrated devices because of lacking three-dimensional space selectivity.Therefore,the high localization and three-dimensional space selectivity of ultrafast laser,as well as the unique photo-thermal properties of PTR glass and subsequent thermal treatment,can make PTR glass have a wider application prospect in the field of integrated device fabrication.In this dissertation,based on the advantages of ultrafast laser modification technology of transparent materials,the photochemical process of PTR glass with ultrafast laser local regulation has been mainly investigated.We focus on the evolution mechanism of defects and nanocrystals during the nonlinear photo-thermal process,and further explore the nonlinear photo-thermal properties of rare earth doped PTR glass and its application in the field of integrated optics.The major content and innovative results of this dissertation are as follows:(1)Based on the nonlinear photochemical response of PTR glass,the dynamic growth process of the color center and silver nanoparticles in the PTR glass after being ultrafast laser Bessel beams irradiated and thermal treated has been systematically investigated.The nonlinear photo-thermo-induced crystallization mechanism based on ultrafast laser exposure has been explored,and compared with UV exposure.The characterization results and theoretical analysis preliminarily confirm that such treatment of PTR glass leads to the formation of the core with silver nanoparticles while the shell consists of Na F with an average size of 5 nm in the focus area.By controlling the pulse energy and pulse width,the size and concentration of silver nanoparticles have been regulated.Furthermore,on the basis of the long non-diffraction transmission distance,a transmission volume Bragg gratings with the maximum diffraction efficiency of 95.1%has been fabricated by optimizing laser parameters,indicating the superiority of local regulation and diffraction property of PTR glass undergoing ultrafast laser irradiation.(2)The effects of CeO₂ and Sb₂O₃ on the photochemical response have been investigated by preparing different doped PTR glass samples.The nonlinear photo-thermo-induced crystallization process of different doped samples has been compared and analyzed,and the roles of CeO₂ and Sb₂O₃ in the ultrafast laser exposure process are clarified:samples doped with a small amount of CeO₂ leads to more defects in the laser exposure process,which leads to the increase of refractive index modulation;while the sample co-doping with CeO₂ and Sb₂O₃ can produce more silver atoms and silver molecular clusters.A more complete nonlinear photo-thermo-induced crystallization mechanism of PTR glass has been established,and proposes that cerium ions,antimony ions and other multivalent ions could be involved in the photoelectron generation and transfer during ultrafast laser exposure.By controlling the pulse energy,it is further proved that CeO₂ can effectively improve the nonlinear absorption of near-infrared femtosecond laser in ultrafast laser irradiated PTR glass,and it participates in the electron generation and transfer process.This work has important guiding significance for optimization of glass compositions and the preparation of three-dimensional micro-nano structures in PTR glass by employing ultrafast laser.(3)Based on ultrafast laser beam space reshaping technology,the nonlinear photo-thermal response behavior of Nd-PTR glass doped with rare earth ions has been investigated under different focal field distributions.On this basis,using the refractive index modulation characteristics of Nd-PTR glass by ultrafast laser,tubular depressed cladding optical waveguide and double-line optical waveguide have been fabricated.By optimizing the writing parameters,the single mode optical waveguide device with good performance is obtained,which would be a basic work for the design of new optical waveguide structures with a large refractive index difference.Based on the saturable absorption characteristics of silver nanoparticles,a saturable absorber has been prepared in Nd-PTR glass by ultrafast laser,and the stable passive Q-switching output has been achieved in Nd:YVO₄ laser.The maximum average output laser power is 173.8 m W and the minimum pulse width is 205 ns.The work has greatly promoted the fabrication and industrial application of monolithic integrated laser and waveguide devices.