| Since Faraday discovered the magneto-optical effect,the application of magnetooptical devices has become an indispensable part of optical communication and integrated optical paths.As the core of magneto-optical devices,magneto-optical materials play a decisive role in the performance of the devices.Because of its high transmittance,excellent magneto-optical properties and high temperature stability,magneto-optical crystals in magneto-optical materials occupy the most important position in the manufacture of all kinds of magneto-optical devices.Based on this,this thesis studies the preparation of Tb3Ga5O12(TGG)crystal which is widely used in magneto-optical devices,and the next generation of advanced substitute,hot magneto-optical crystal Tb3Sc2Al3O12(TSAG)crystal.It mainly includes the construction of temperature field,the exploration of polycrystalline synthesis technology and the growth of large size single crystal by Czochralski(CZ)method.The crystal growth equipment,process,color center and component segregation phenomenon were studied in detail,and the properties of growing TGG crystals were characterized and analyzed.The research on TGG crystal includes the use of solid phase sintering process to determine the synthesis process of polycrystalline material suitable for the growth of TGG crystal,the sintering time and sintering temperature were studied.The prepared powders were characterized by X-ray diffraction to verify the degree of polycrystalline synthesis.The high quality polycrystalline powder suitable for the growth of magnetooptic crystal has been prepared.A series of large size TGG crystals(Φ76 mm*L100 mm)were grown in different atmospheres by the pull-up method.The mechanism of color center,fracture and spiral growth is discussed.The results show that the color center of TGG crystal is closely related to the atmosphere and the composition of raw materials.By increasing the content of Ga2O3 to 6.5%and increasing the sintering temperature of the polycrystalline material,large size colorless TGG crystals can be obtained.In order to improve the optical properties of the crystal,the suitable annealing conditions of TGG crystal were studied for the first time.The results show that the color center of TGG crystal can be eliminated by selecting appropriate annealing conditions.TGG crystal samples of different sizes and specifications were prepared by studying the crystal processing technology and conducting orientation,cutting and polishing of the growing crystals to be used for performance characterization.The results showed that the transmittance of the grown TGG crystals was more than 80%,and the extinction ratio was above 35dB.The research on TSAG includes the use of solid phase sintering process to determine the synthesis process of polycrystalline material suitable for the growth of TSAG crystal,the sintering time and sintering temperature were studied.A series of TSAG with different sizes were grown by using Nd:YAG crystal as seed crystal in high purity Ar atmosphere by means of drawing method by setting up appropriate temperature field and designing reasonable technological parameters.Finally,the large size TSAG crystal(Φ40 mm*L60 mm)without cracking,bubbles and color center was successfully obtained.The segregation of Sc element and Al element during the growth of terbium scandium aluminum garnet crystal was studied by phase analysis and content determination of the material inside and bottom of the crystal.The size of the grown TGG and TSAG crystal are both in the leading position at home and abroad.The crystals performance is excellent and can fully meet the requirements of making magneto-optical devices. |
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