Growth And Properties Characterization Of Novel Visible Near-Infrared TAGG Magneto-optic Crystal By Micro-pulling-down Method

The optical isolator based on non-reciprocal Faraday effect can effectively prevent the reflected light in the process of laser transmission,which can stabilize the laser source and output power,ensure the safe operation of the system and reduce the power consumption caused by stimulated Brillouin scattering of the laser.Magneto-optical materials,the key material to determine the performance of optical isolators,are considered as the "root" and "soul" of optical isolators,and their research and application have been driving the update and development of optical isolators.Garnet structure magneto-optical crystals have become the preferred materials for high-efficiency magneto-optical isolators because of their excellent magneto-optical properties.However,the current commercial Tb3Ga5O12(TGG)crystal is difficult to meet the future development needs of high-power and miniaturized devices.The incongruent melting nature of Tb3Al5O12(TAG)crystal makes it difficult to grow.And Tb3Sc2Al3O12(TSAG)series crystals are easy to crack,and the expensive raw materials also limit the commercial application of these crystals.At present,our country’s development trend toward high-power magnetooptical crystals and devices will not change,but key magneto-optical crystals and devices depend on imports to a certain extent,so the research and development of magneto-optical crystals with higher quality,higher performance and lower cost is imminent.This paper complies with the development trend of the forefront in magneto-optical materials research,improves the "weakness" of TGG crystal performance which is difficult to meet the development needs,overcomes the "difficulty" of TAG incongruent melting,and cleans the "blocking point" of TSAG series crystals which are easy to crack and expensive raw materials.Tb3AlxGa5-xO12(TAGG)series magneto-optical crystals with high magneto-optical properties and congruent melting nature are prepared by the micro-pulling-down(μ-PD)method for the first time.The structure,quality,and thermal,optical and magneto-optical properties of the crystal are systematically analyzed.The results show that the magneto-optical properties of TAGG crystals are significantly better than those of traditional commercial TGG crystals,and TAGG crystals have great application prospects in the visible-near-infrared(VISNIR)band.TAGG crystals are expected to promote the development of high-performance magneto-optical crystals and lays the foundation for the rapid development of high-power laser systems,optical fiber communication and precision optical measurement systems.This paper consists of five chapters,which mainly cover the following aspects.In chapter 1,we reviewed the basic knowledge about magneto-optic crystals,the current research situation of terbium-based garnet crystals at home and abroad,and the micro-pullingdown technology.In addition,the research background of TAGG crystals,the basis of topic selection and main contents of this paper are introduced.In chapter 2,the synthesis method of TAGG poly crystalline materials and the experimental raw materials used in the preparation process,crystal growth steps and characterization means are introduced in detail.In chapter 3,firstly,the optimum process conditions for synthesis of polycrystalline raw materials were explored.Then,TAGG(x=1.5,2.25,3,3.75)crystals were grown after in-depth study of growth conditions including temperature field,atmosphere and process parameters.The XRD characterization results show that,currently,the highest concentration of aluminum doping that could grow pure phase crystals by the μ-PD method was 60 at.%,i.e.TAGG(x=3).The TAGG(x=3)crystal was also optimized in terms of pulling speed and seed crystal selection.It provides effective reference for growth of other gallium containing crystals.In Chapter 4,the composition,structure and crystalline quality of TAGG(x=3)were characterized.At the same time,the mechanical properties,thermal properties,optical and magneto-optical properties of the crystal were systematically investigated.The results show that the TAGG crystals have better thermal properties,higher transmittance,and larger Verdet constants than the conventional TGG crystal,making them promising low-cost magneto-optical materials for high-power laser systems.In chapter 5,the main conclusions,innovations of the research and work to be done are summarized.