| Doped lanthanon potassium gadolinium tungstate crystal (KGd(WO4)2(abbreviated asKGW), which contains a series of unique properties is gradually getting scientificcommunity’s attention as being an extremely promising new laser material. This papermainly focuses on the growth of doped lanthanon potassium gadolinium tungstate crystaland a number of new crystal structure design and preparation.1. Paper first takes a brief overview and discussion on laser crystal and crystal growthtechnology, introduces the fundamental nature of the KGW crystal, and discusses the KGWcrystal growth method and the choice of growth conditions. Top-seeded solution growth andmolten salt Czochralski method are more detailed analyzed.2. Second, from the crystal growth, defect studies, spectroscopic properties and laserexperiments, paper goes on to induce and discuss KGW crystal related domestic and foreignliteratures; introduces domestic and foreign installations in the crystal growth status quo,including design of temperature field, machine design, automation control, etc., and itsfuture development is also expected.3. Paper describes KGW crystal’s specific research work of growth, discusses thetechnical problems encountered from experiments and provides appropriate solutions, whichspecifically includes:1) Transformation of Crystal Growth Laboratory:Transform the crystal growth chamber and control room according to the mechanicalvibration, temperature fluctuations, humidity, dust and other special requirements oflaboratory environment by using molten salt method. Paper also describes the experiment byusing two kinds of temperature control instrument for their own characteristics.2) Design of Crystal Growth Furnace:Discuss the molten salt furnace design requirements; According to KGW crystal growthcharacteristics, design a large heat capacity growth furnace of Φ650×600mm and discusstight winding method for the heat body, thermocouple selection and placement, crucible design. Preparatory exploration on two key technical points of crystal growth furnace designand preparation:Furnace structural design: The goal is to find the best temperature gradientdistribution by considering the calculation of heating power, heating elementdesign, temperature zone layout and power matching, etc.; Concentrating on liningmaterial selection, precise calculation of furnace wall and the insulation layers offire-resistant materials interface temperature, thickness and heat flow, thermalfield to ensure the maintenance and repair could be convenient and practical.High-precision temperature control system：Goal is to ensure that long time(within3months of growth cycle) temperature fluctuation is less than0.1°C.Because crystal growth due to thermal hysteresis of the system is a great system,and the thermal lag time in the entire crystal growth process of changing isnonlinear, the key is to control the thermal lag effect of the controlled system.3）Temperature Field DesignPaper discusses the theoretical basis for the design of temperature field and the need toconsider specific issues, and by changing the heating wire surround mode density levelcrucible relative to the location of heating elements, thermal insulation above the cruciblemeans to achieve the temperature field control, finally passed Al2O3multilayer insulationtube, bumpers, as well as the formation of a post-heater insulation system can be flexiblycombined to meet the KGW crystal growth requirements.4) The design and preparation of computer-aided multi-flux method crystalgrowth system:I also feel great intensity of work through the crystal growth process and take a longperiod of time to be skilled. Can computer-aided design and prepare a set of multi-fluxmethod crystal growth system to solve this problem? Along with this idea and through thecareful guidance from teachers and strong supports from students, in the latter part of mythesis work, I carry out this research and make some progress by studying the systemhardware components, such as weighing systems, signal amplifier, power control systems,etc.; According to the application requirements, I set up and analyze system management,equipment management, communications management, data processing and10otherfunctional modules by using software development tools, Borland Delphi7Enterpise,database, Microsoft Access2000. 5) Material SynthesisFirst discuss the crystal growth flux method’s basic principles of choice and selectionsteps, compare the character of selective flux for growing KGW crystal; Re-determine andvalidate the close linked of current growth phase diagram K2W2O7system liquid line;Discuss Nd3+doping concentration and fluorescence intensity of the relationship betweenthe choice of the best Nd3+doping concentration; Explain KGW ratio of raw materialcomponents, specific raw material preparation process, and comparison of synthetic rawmaterials and standard XRD good KGW spectra. Find out that the effect of co-operationKGW material will have been able to meet the needs of crystals.6) The technology of growthStudy the various concrete steps and key technologies of KGW crystal’s growth indetail, including seed preparation, raw material-based material, test growth, crystal seed,different growth stages of casting speed, rotation rate, the choice of cooling rate, crystaldiameter crystal growth control and post-processing techniques; Taking K2W2O7ascosolvent, using molten salt Czochralski method, I successfully get a series of high-qualitydoped KGW crystal, Nd-doped concentrations are1,1.6,2,3,3.5,5,8at%of different crystalsand its size up to60×60×30mm3, optical homogeneity up to1.25×10-5and under the5mw red light irradiation it showing no scattering channel。7) Defects of crystalDiscuss three major defects of KGW crystal growth by using Molten salt Czochralskimethod, such as packages, cracking and growth texture’s token, appearing reason andpossible elimination methods. Propose to use control neck and release shoulder techniques toeffectively improve the internal quality of crystal during the seeding period.8) Large-size wafer processingBrief describes the process flow on crystal device, including orientation, cutting, coarsegrinding, polishing, coating and so on. Major focus on describing KGW crystal’s roughgrinding polishing, pre-polishing, machining flatness and parallelism, processing, finish andother key technique points; After processing, get surface flatness of0.114λ, parallel degree4.4", surface roughness0.556nm’s KGW crystal.9) The test of Nd: KGW crystal optical and spectral properties.Measure important parameters of laser operating such as absorption, emission section,wavelength, peak width, quantum efficiency and lifetime; Get Nd: KGW crystal’s fluorescence emission cross-section of1.483×10-20cm2at1067nm, half-peak width:15nm;absorption wavelength810nm at810nm and a half peak width14nm, absorptioncross-section1.27831×10-20cm2, fluorescence lifetime110μs.10) Laser experimentFirst, Test the crystal bar under the cavity condition, obtain the relations of outputpower and pump power by using different transmission plane mirror;Second, the Q-experiment, under static state conditions, using a differenttransmission plane mirror as the output mirror, get the output power and pumppower diagram and the highest conversion efficiency of56%;Under the Q-conditions, where pulse repetition frequency is10Hz, pump pulseduration is385μs, the output power increases with pump power; When pumppower is small, the output power rise fast; When pump power is high, the outputpower rise slow; During the experiment, the maximum conversion efficiency is11.4%;This experiment proofs that Nd: KGW has large energy output, high conversionefficiency, which can be used to develop high-efficiency small-scale lasers.11) The final chapter takes an outlook of improving the KGW crystal quality and sizeand pointing the direction of research for next stage of work.4. In the latter part of this thesis, under the guidance of instructors and through thehydrothermal synthesis of the five kinds of coordination polymers, I carry out crystalstructure determination and description in order to establish the foundations for next stage ofstudy. |
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