Large-size yttrium lithium fluoride single crystal growth system and process

Abstract

The application relates to a large-size yttrium lithium fluoride single crystal growth system and process, and belongs to the technical field of artificial crystal growth. The system comprises a furnace body, a crucible, a temperature field subsystem, a vacuum subsystem, a mechanical transmission subsystem, an automatic growth control subsystem and a main control subsystem. The single crystal growth system provided by the application is cooperatively operated by the temperature field subsystem, the vacuum subsystem, the mechanical transmission subsystem and the automatic growth control subsystem under the unified coordination of the main control subsystem, so as to jointly create a crystal growth environment which can be accurately controlled and is stable and reliable. Through a pretreatment process comprising raw material pre-melting, cleaning and weighing and supplementing of raw materials, and in combination with the variable-speed rotation technology of the crucible in the growth process, the purity and the component uniformity of the melt are significantly improved.

Description

Technical Field

[0001] This application relates to the technical field of artificial crystal growth, and in particular to a large-size lithium yttrium fluoride single crystal growth system and process. Background Technology

[0002] Lithium yttrium fluoride (YLiF4, or YLF for short) crystal is an excellent laser matrix material that can be doped with various rare earth ions (such as neodymium and thulium) to achieve laser output in multiple bands from ultraviolet to near infrared at room temperature. It is widely used in scientific research, industry, medicine and laser nuclear fusion.

[0003] The main methods for growing doped YLF crystals both domestically and internationally include the Czochralski method and the crucible lowering method. While the former can produce high-quality single crystals, it requires extremely high control over equipment and processes for growing large-sized crystals (e.g., those with a diameter ≥ 50 mm). The latter, while capable of growing larger crystals, has a low single crystal yield and poor crystal quality.

[0004] Currently, the domestically produced YLF-related crystals with a stable size of φ30~40mm are generally of poor quality or have low yields. Existing technologies, in order to overcome these problems, primarily reduce the number and thickness of insulation layers in all directions of the temperature field and raise the position of the crucible relative to the heater to increase the temperature gradient within the melt and enhance natural convection. This method is relatively effective when growing small-sized crystals, but it is difficult to achieve the desired size for growing large-sized crystals.

[0005] Therefore, there is an urgent need for a new large-size lithium yttrium fluoride single crystal growth system. Summary of the Invention

[0006] In order to produce large-sized crystals by reducing the number and thickness of insulation layers in each direction of the temperature field, this application provides a large-sized lithium yttrium fluoride single crystal growth system and process.

[0007] In a first aspect, this application provides a large-size lithium yttrium fluoride single crystal growth system, which adopts the following technical solution: A large-size lithium yttrium fluoride single crystal growth system, comprising: Furnace body; The crucible is located inside the furnace body; A temperature field subsystem includes a heating component and a heat preservation component. The heating component is located inside the furnace body and raises the temperature inside the furnace body. The heat preservation component includes an inner heat preservation cylinder and an outer heat preservation cylinder. The crucible is located inside the inner heat preservation cylinder. The heating component is located between the inner heat preservation cylinder and the outer heat preservation cylinder. The outer heat preservation cylinder includes a graphite base plate, a graphite side plate, a first graphite cover plate, and a second graphite cover plate. The graphite base plate is located below the first graphite cover plate, the first graphite cover plate is located below the second graphite cover plate, and the graphite side plate is disposed between the graphite base plate and the first graphite cover plate, and between the first graphite cover plate and the second graphite cover plate. A vacuum subsystem, located outside the furnace body, is used to provide a vacuum environment to the interior of the furnace body; The mechanical transmission subsystem includes a seed crystal lifting and rotating mechanism and a crucible lifting and rotating mechanism. The seed crystal lifting and rotating mechanism includes a seed crystal shaft, and the crucible lifting and rotating mechanism includes a crucible shaft. The shortest connecting line between the top and bottom ends of the furnace body is in the vertical direction. Both the seed crystal shaft and the crucible shaft can move in the vertical direction. The axes of the seed crystal shaft and the crucible shaft are in the vertical direction. Both the seed crystal shaft and the crucible shaft rotate along their own axes. The bottom end of the seed crystal shaft passes through the top of the furnace body and is used to connect the seed crystal. The top end of the crucible shaft passes through the bottom of the furnace body and is used to connect the crucible. An automatic growth control subsystem is located outside the furnace body and is used to control the entire process of seed crystal growth; The main control subsystem is located outside the furnace body and is electrically connected to the vacuum subsystem, mechanical transmission subsystem, and automatic growth control subsystem.

[0008] By adopting the above technical solution, a high-precision, high-stability, and highly automated growth device was constructed. This device can precisely control the core parameters of crystal growth, such as the thermal field, atmosphere, pulling, and rotation, providing fundamental equipment support for growing large-size, low-defect, and highly uniform yttrium lithium fluoride single crystals with a diameter ≥50mm.

[0009] Optionally, the automatic growth control subsystem includes a high-precision electronic scale, which is fixed to the top of the seed crystal shaft and used to monitor the weight during the crystal growth process in real time.

[0010] By adopting the above technical solution, the high-precision electronic scale can monitor the weight change during the crystal growth process in real time, providing the most direct growth status signal for the automatic growth control subsystem, ensuring that the crystal grows to the preset size (such as 50mm) and has a regular shape.

[0011] Optionally, the seed crystal lifting and rotating mechanism further includes a grating ruler, which is located to the side of the seed crystal axis and is used to directly measure the actual position of the seed crystal axis.

[0012] By adopting the above technical solution, the grating ruler directly measures the actual position of the seed crystal axis, which improves the control accuracy of seed crystal positioning, crystal dropping and pulling rate, and provides key positional guarantee for precise control of crystal growth interface and growth rate.

[0013] Optionally, both the crucible lifting and rotating mechanism and the seed crystal lifting and rotating mechanism include a sealing element, which is disposed on the furnace body, and both the crucible shaft and the seed crystal shaft pass through the sealing element.

[0014] By employing the above technical solution, the sealing components installed on the furnace body ensure that the vacuum level or protective atmosphere inside the furnace is not disrupted during the lifting and rotation of the seed crystal shaft and crucible shaft. This is crucial for preventing external gas contamination and maintaining a stable growth environment, and is a prerequisite for obtaining high-optical-quality crystals.

[0015] Optionally, the vacuum subsystem includes a backing pump, a high vacuum pump, a vacuum pipeline, a vacuum valve, and a vacuum gauge. The high vacuum pump is connected to the furnace body via the vacuum pipeline, and the backing pump, the vacuum valve, and the vacuum gauge are all mounted on the vacuum pipeline.

[0016] By adopting the above technical solution, using a combination of a backing pump and a high-vacuum pump, the furnace can be quickly and efficiently pumped to a high vacuum, creating conditions for subsequent raw material degassing and high-purity atmosphere growth.

[0017] Secondly, this application provides a process for growing large-size lithium yttrium fluoride single crystals, employing the following technical solution: A process for growing large-size lithium yttrium fluoride single crystals, applied to the aforementioned large-size lithium yttrium fluoride single crystal growth, includes the following steps: S1. Temperature field cleaning: Cleaning the furnace body and the equipment inside the furnace body; S2. Raw material pretreatment: The proportioned raw materials are loaded into the large crucible of the melting equipment for pre-melting. S3, Pre-melting process: Under high vacuum (below 8.0×10⁻⁶) conditions. -4 The temperature is raised to 250-300℃ while carbon tetrafluoride gas is introduced as the reaction gas. Then, argon gas is introduced into the furnace and the temperature is raised again until the raw material begins to melt. After the raw material is completely melted, the melt temperature is adjusted to 850-900℃ and held for 24 hours. Then, the temperature is lowered for 8-12 hours to room temperature. After pre-melting, the raw material is removed from the crucible and weighed to calculate the amount of lithium fluoride volatilized. The black volatiles on the surface of the raw material are cleaned, and the lumpy raw material is broken into small pieces and stored in vacuum packaging bags. S4. Loading the Furnace: Weigh an appropriate amount of pre-melted material, replenish the weight of the lithium fluoride lost through burn-off, and then load them together into the crucible according to the normal operating sequence; after the furnace is closed, begin evacuating the furnace sequentially from low vacuum to high vacuum according to process requirements, achieving a high vacuum of 3.0 × 10⁻⁶. -3 After Pa, the temperature is raised to 250-300℃ and kept constant for 12 hours; S5. Gas filling: Fill the furnace with high-purity argon (BIP grade) at a flow rate of 7L / min until the furnace pressure is -50 kPa to -60 kPa, then stop filling with argon; then fill the furnace with high-purity carbon tetrafluoride gas (above 5N) at a flow rate of 5L / min for 1-5s, then stop filling with argon. S6. Increase temperature: Set the temperature inside the crucible to 880℃ for 12 hours, and then maintain the temperature. S7. Melt treatment: After the raw material has completely melted, adjust the crucible position to the crystal-leading crucible position; set the crucible rotation speed from -20 rpm to +20 rpm, with an acceleration of 0.5 rpm / s; continue to maintain the temperature for 5 hours. S8. Seed crystal lowering: After 5 hours of constant temperature, set the crucible speed to +5 rpm for constant speed rotation, change the heater power to crystal pulling power, and set the seed crystal rod speed to 12-18 rpm; lower the seed crystal to 50 mm from the liquid surface at a speed of 10 mm / min, and hold for 10 minutes; then change the seed crystal rod pulling speed to 5 mm / min, lower it by 10 mm every 10 minutes until the bottom of the seed crystal is 1-5 mm from the liquid surface, and hold for 10 minutes. S9. Crystal Introduction: Lower the seed crystal to the liquid surface to begin crystal introduction; observe the solid-liquid interface state and the weight change displayed on the electronic scale; adjust the power to the point where the seed crystal is slightly melted, turn on the automatic growth control subsystem, and begin automatic necking; set the seed crystal rod lifting rate to 0.5-1 mm / h, and set the second graphite cover plate lifting speed to 0.6-0.8 times the seed crystal rod speed, and move it upward synchronously; set the crystal diameter to gradually increase to the seed crystal size after lifting 3-5 mm; set the shoulder angle of the automatic growth control subsystem to gradually increase from 30° at the time of crystal introduction to 60° at the time of shoulder turning, set the crystal diameter of the constant diameter stage to gradually decrease from 52 mm to 50 mm, and the constant diameter length to 120-150 mm; set the parameters in the automatic growth control subsystem such as the crystal length of each stage, calculate and set the crucible lifting speed to ensure constant liquid level growth; S10. Cooling: After the crystal has grown to the target size or weight, shut down the automatic growth control subsystem and cool the furnace at a rate of 10-11.5℃ / h. S11. Furnace dismantling: After the crystal temperature drops to room temperature, remove the crucible from the furnace to take out the crystal, clean the furnace body and inside the furnace, and prepare for the next batch of crystal growth.

[0018] Optionally, in S1, a vacuum cleaner and a lint-free cloth are used to clean the furnace body and the equipment inside the furnace.

[0019] Optionally, in S2, a total weight of raw materials (with a purity of 4N) required for 9-10 heats of crystal growth is weighed and pre-melted.

[0020] Optionally, in S7, when adjusting the crucible position to the crystal-leading crucible position, ensure that the melt surface is 5-10 mm away from the top of the heating zone.

[0021] Optionally, in S7, when adjusting the crucible position to the crystal-leading crucible position, ensure that the melt surface is 5-10 mm away from the top of the heating zone.

[0022] In summary, this application includes at least one of the following beneficial technical effects: Under the unified coordination of the main control subsystem, the entire system comprises a temperature field subsystem, a vacuum subsystem, a mechanical transmission subsystem, and an automatic growth control subsystem, working together to create a precisely controllable, stable, and reliable crystal growth environment. Simultaneously, the introduction of high-precision electronic scales and optical grating rulers enables real-time monitoring and closed-loop feedback of key parameters in the growth process, significantly improving control accuracy and automation.

[0023] By employing a pretreatment process that includes raw material pre-melting, cleaning, and weighing replenishment, combined with crucible rotation technology during the growth process, the purity and compositional uniformity of the melt are significantly improved. This process effectively removes volatile impurities from the raw materials and precisely compensates for the loss of volatile components (lithium fluoride), thereby greatly improving the integrity of the crystal's microstructure, compositional uniformity, and consistency of growth quality across multiple batches.

[0024] By employing a series of meticulously controlled process steps, including staged seeding, automatic necking, smooth gradient shoulder formation, and programmed cooling, and by closely coordinating with the temperature field characteristics of the equipment, stable crystal growth and low-stress controllable growth were achieved, ultimately resulting in the successful preparation of large-size single-crystal blanks with excellent performance. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the single crystal growth system provided in this application; Figure 2 This is a flowchart of the single crystal growth process provided in this application.

[0026] Explanation of reference numerals in the attached drawings: 1. Furnace body; 2. Heater; 3. Insulated inner cylinder; 4. Graphite bottom plate; 5. Graphite side plate; 6. First graphite cover plate; 7. Second graphite cover plate; 8. Seed crystal shaft; 9. Crucible shaft; 10. Foreboard pump; 11. Vacuum pump; 12. Graphite insulation felt. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1-2 This application will be described in further detail.

[0028] refer to Figure 1 This application discloses a large-size lithium yttrium fluoride single crystal growth system. The system includes a furnace body 1, a crucible, a temperature field subsystem, a vacuum subsystem, a mechanical transmission subsystem, an automatic growth control subsystem, and a main control subsystem.

[0029] Both the crucible and the temperature field subsystem are located inside the furnace body 1, and at its center. The temperature field subsystem includes a heating assembly and a heat preservation assembly. The heating assembly includes multiple heaters 2, some of which are located in the middle of the furnace body 1 and are distributed circumferentially around the crucible, while others are located at the bottom of the furnace body 1 and below the crucible. The heat preservation assembly consists of an inner heat preservation cylinder 3 and an outer heat preservation cylinder. The inner heat preservation cylinder 3 is fixed inside the furnace body 1 and is divided into two parts, with the upper part being larger than the lower part. The crucible is located inside the inner heat preservation cylinder 3. And it is located in the upper part; the outer insulation cylinder includes a graphite bottom plate 4, a graphite side plate 5, a first graphite cover plate 6, a second graphite cover plate 7 and a graphite insulation felt 12. The first graphite cover plate 6 and the second graphite cover plate 7 are both located at the top of the furnace body 1, and the first graphite cover plate 6 is located below the second graphite cover plate 7. The first graphite cover plate 6 is in contact with the top of the inner insulation cylinder 3. The heater 2 is located between the inner insulation cylinder 3 and the outer insulation cylinder. More specifically, the heater 2 is located between the graphite side plate 5 and the graphite bottom plate 4. The graphite insulation felt 12 is located at the bottom of the furnace body 1 to prevent the heat inside the furnace from escaping.

[0030] The second graphite cover plate 7 can be raised and lowered in the vertical direction, with a lifting stroke of 100mm and a lifting speed of 0.01-50mm / min.

[0031] The graphite base plate 4, graphite side plate 5, first graphite cover plate 6, second graphite cover plate 7, and graphite insulation felt 12 are all formed using isostatic pressing and have undergone passivation treatment, with an ash content ≤20ppm. Furthermore, the surface of the graphite insulation felt 12 requires a coating treatment.

[0032] When growing Nd with a diameter of 50 mm, the thickness of the graphite side plate 5 is 5 mm, the thickness of the graphite bottom plate 4 is 3-4 mm, and the thickness of the first graphite cover plate 6 and the second graphite cover plate 7 are both 5 mm, with a spacing of 10 mm between them. The inner diameter of the graphite crucible is 120 mm, and the thickness is 4 mm. The maximum output heating power of the heater 2 located on the side of the crucible is 20 kW, and the maximum output heating power of the heater 2 located below the crucible is 15 kW.

[0033] The vacuum subsystem includes a vacuum pipeline and, sequentially arranged on the vacuum pipeline, a high vacuum pump 11, a backing pump 10, vacuum valves, and a vacuum gauge. The vacuum pipeline connects to the interior of the furnace body 1. The vacuum gauge is used to measure the vacuum level inside the furnace body 1. The backing pump 10 first reduces the pressure inside the furnace body 1 to a certain vacuum level, and then the high vacuum pump 11 further reduces the pressure inside the furnace body 1 to a specified vacuum level (e.g., pre-melting below 8.0 × 10⁻⁴ Pa, or purging after 3.0 × 10⁻³ Pa). The mechanical transmission subsystem includes a seed crystal lifting and rotating mechanism and a crucible lifting and rotating mechanism. The seed crystal lifting and rotating mechanism includes a seed crystal shaft 8, a first rotating body that drives the seed crystal shaft 8 to rotate, and a first moving body that drives the seed crystal shaft 8 to move. Since the first rotating body and the first moving body are existing technologies, they will not be described in detail. Similarly, the crucible lifting and rotating mechanism includes a crucible shaft 9, a second rotating body that drives the crucible shaft 9 to rotate, and a second moving body that drives the crucible shaft 9 to move. The second rotating body and the second moving body will not be described in detail.

[0034] The bottom end of the seed crystal shaft 8 is connected to a seed crystal chuck, which holds the seed crystal inside the crucible. The top end of the crucible shaft 9 is connected to the bottom of the crucible.

[0035] The automatic growth control subsystem includes a high-precision electronic scale and its accessories (temperature sensor and PLC, etc.). The high-precision electronic scale can monitor the minute weight increase during seed crystal growth in real time. Since the automatic growth control system is existing technology, it will not be described in detail further. The automatic growth control system uses an ADC program to automatically control the crystal growth processes such as necking, shoulder formation, and equal diameter determination by weighing the crystal using a high-precision electronic scale (voltage signal, accurate to 6 decimal places).

[0036] The main control subsystem is primarily used to precisely control the output heating power of the transformer, with a power output error of ≤0.02%.

[0037] The implementation principle of a large-size lithium yttrium fluoride single crystal growth system in this application embodiment is as follows: the temperature field subsystem constructs a specific temperature gradient that meets the growth requirements of large-size YLF crystals through a unique heat preservation structure and a synchronously movable graphite cover plate; the vacuum subsystem provides a high vacuum to ensure ultra-high environmental cleanliness; the mechanical transmission subsystem realizes melt stirring and precise control of seed crystals; and the automatic growth control subsystem relies on the real-time feedback of a high-precision electronic scale and a grating ruler to perform closed-loop control of the pulling and heating power. Finally, under fully automated and precise control, the stable growth of high-quality, large-size lithium yttrium fluoride single crystals is achieved.

[0038] refer to Figure 2 This application also discloses a process for growing large-size lithium yttrium fluoride single crystals, including the following steps: S1. Temperature field cleaning: Cleaning the furnace body and the equipment inside the furnace body; S2. Raw material pretreatment: The proportioned raw materials are loaded into the large crucible of the melting equipment for pre-melting. S3, Pre-melting process: Under high vacuum (below 8.0×10⁻⁶) conditions. -4 The temperature is raised to 250-300℃ while carbon tetrafluoride gas is introduced as the reaction gas. Then, argon gas is introduced into the furnace and the temperature is raised again until the raw material begins to melt. After the raw material is completely melted, the melt temperature is adjusted to 850-900℃ and held for 24 hours. Then, the temperature is lowered for 8-12 hours to room temperature. After pre-melting, the raw material is removed from the crucible and weighed to calculate the amount of lithium fluoride volatilized. The black volatiles on the surface of the raw material are cleaned, and the lumpy raw material is broken into small pieces and stored in vacuum packaging bags. S4. Loading the Furnace: Weigh an appropriate amount of pre-melted material, replenish the weight of the lithium fluoride lost through burn-off, and then load them together into the crucible according to the normal operating sequence; after the furnace is closed, begin evacuating the furnace sequentially from low vacuum to high vacuum according to process requirements, achieving a high vacuum of 3.0 × 10⁻⁶. -3 After Pa, the temperature is raised to 250-300℃ and kept constant for 12 hours; S5. Gas filling: Fill the furnace with high-purity argon (BIP grade) at a flow rate of 7L / min until the furnace pressure is -50 kPa to -60 kPa, then stop filling with argon; then fill the furnace with high-purity carbon tetrafluoride gas (above 5N) at a flow rate of 5L / min for 1-5s, then stop filling with argon. S6. Increase temperature: Set the temperature inside the crucible to 880℃ for 12 hours, and then maintain the temperature. S7. Melt treatment: After the raw material has completely melted, adjust the crucible position to the crystal-leading crucible position; set the crucible rotation speed from -20 rpm to +20 rpm, with an acceleration of 0.5 rpm / s; continue to maintain the temperature for 5 hours. S8. Seed crystal lowering: After 5 hours of constant temperature, set the crucible speed to +5 rpm for constant speed rotation, change the heater power to crystal pulling power, and set the seed crystal rod speed to 12-18 rpm; lower the seed crystal to 50 mm from the liquid surface at a speed of 10 mm / min, and hold for 10 minutes; then change the seed crystal rod pulling speed to 5 mm / min, lower it by 10 mm every 10 minutes until the bottom of the seed crystal is 1-5 mm from the liquid surface, and hold for 10 minutes. S9. Crystal Introduction: Lower the seed crystal to the liquid surface to begin crystal introduction; observe the solid-liquid interface state and the weight change displayed on the electronic scale; adjust the power to the point where the seed crystal is slightly melted, turn on the automatic growth control subsystem, and begin automatic necking; set the seed crystal rod lifting rate to 0.5-1 mm / h, and set the second graphite cover plate lifting speed to 0.6-0.8 times the seed crystal rod speed, and move it upward synchronously; set the crystal diameter to gradually increase to the seed crystal size after lifting 3-5 mm; set the shoulder angle of the automatic growth control subsystem to gradually increase from 30° at the time of crystal introduction to 60° at the time of shoulder turning, set the crystal diameter of the constant diameter stage to gradually decrease from 52 mm to 50 mm, and the constant diameter length to 120-150 mm; set the parameters in the automatic growth control subsystem such as the crystal length of each stage, calculate and set the crucible lifting speed to ensure constant liquid level growth; S10. Cooling: After the crystal has grown to the target size or weight, shut down the automatic growth control subsystem and cool the furnace at a rate of 10-11.5℃ / h. S11. Furnace dismantling: After the crystal temperature drops to room temperature, remove the crucible from the furnace to take out the crystal, clean the furnace body and inside the furnace, and prepare for the next batch of crystal growth.

[0039] The beneficial effects of the large-size lithium yttrium fluoride single crystal growth process provided in this application are as follows: I. By employing a pretreatment process that includes raw material pre-melting, cleaning, and weighing replenishment, combined with crucible rotation technology during growth, the purity and compositional uniformity of the melt are significantly improved. This process effectively removes volatile impurities from the raw materials, precisely compensates for the loss of volatile components (lithium fluoride), and eliminates the concentration segregation of dopant ions through forced stirring, fundamentally suppressing the occurrence of component supercooling. This, in turn, greatly improves the integrity of the crystal's microstructure, compositional uniformity, and the consistency of growth quality across multiple batches.

[0040] II. By employing a series of meticulously controlled process steps, including staged seeding, automatic necking and lifting, smooth gradient shoulder formation, and programmed cooling, and in close coordination with the equipment's temperature field characteristics, stable crystal seeding and low-stress controllable crystal growth were achieved. This process ensures a smooth transition and precise dimensional control from seeding to constant diameter stages, while effectively reducing the thermal stress experienced by the crystal during growth and cooling. This results in extremely low internal defect density, a complete and transparent appearance, and ultimately, the successful fabrication of large-size single-crystal blanks with excellent optical properties.

[0041] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A large-size lithium yttrium fluoride single crystal growth system, characterized in that, include: Furnace body (1); The crucible is located inside the furnace body (1); The temperature field subsystem includes a heating component and a heat preservation component. The heating component is located inside the furnace body (1) and raises the temperature inside the furnace body (1). The heat preservation component includes a heat preservation inner cylinder (3) and a heat preservation outer cylinder. The crucible is located inside the heat preservation inner cylinder (3). The heating component is located between the heat preservation inner cylinder (3) and the heat preservation outer cylinder. The heat preservation outer cylinder includes a graphite bottom plate (4), a graphite side plate (5), a first graphite cover plate (6), and a second graphite cover plate (7). The graphite bottom plate (4) is located below the first graphite cover plate (6). The first graphite cover plate (6) is located below the second graphite cover plate (7). The graphite side plate (5) is disposed between the graphite bottom plate (4) and the first graphite cover plate (6) and the first graphite cover plate (6) and the second graphite cover plate (7). A vacuum subsystem is located outside the furnace body (1) and is used to provide a vacuum environment to the interior of the furnace body (1); The mechanical transmission subsystem includes a seed crystal lifting and rotating mechanism and a crucible lifting and rotating mechanism. The seed crystal lifting and rotating mechanism includes a seed crystal shaft (8) and a crucible lifting and rotating mechanism includes a crucible shaft (9). The shortest connecting line between the top and bottom of the furnace body (1) is in the vertical direction. Both the seed crystal shaft (8) and the crucible shaft (9) can move in the vertical direction. The axis of the seed crystal shaft (8) and the crucible shaft (9) is in the vertical direction. Both the seed crystal shaft (8) and the crucible shaft (9) rotate along their own axis. The bottom end of the seed crystal shaft (8) passes through the top of the furnace body (1) and is used to connect the seed crystal. The top end of the crucible shaft (9) passes through the bottom of the furnace body (1) and is used to connect the crucible. An automatic growth control subsystem is located outside the furnace body (1) and is used to control the entire process of seed crystal growth; The main control subsystem is located outside the furnace body (1) and is electrically connected to the vacuum subsystem, the mechanical transmission subsystem and the automatic growth control subsystem.

2. The large-size lithium yttrium fluoride single crystal growth system according to claim 1, characterized in that: The automatic growth control subsystem includes a high-precision electronic scale, which is fixed to the top of the seed crystal shaft (8) and used to monitor the weight of the crystal during the growth process in real time.

3. The large-size lithium yttrium fluoride single crystal growth system according to claim 2, characterized in that: The seed crystal lifting and rotating mechanism also includes a grating ruler, which is located to the side of the seed crystal axis (8) and is used to directly measure the actual position of the seed crystal axis (8).

4. The large-size lithium yttrium fluoride single crystal growth system according to claim 3, characterized in that: Both the crucible lifting and rotating mechanism and the seed crystal lifting and rotating mechanism include a sealing element. The sealing element is disposed on the furnace body (1), and both the crucible shaft (9) and the seed crystal shaft (8) pass through the sealing element.

5. The large-size lithium yttrium fluoride single crystal growth system according to claim 4, characterized in that: The vacuum subsystem includes a forepump (10), a high vacuum pump (11), a vacuum pipeline, a vacuum valve, and a vacuum gauge. The high vacuum pump (11) is connected to the furnace body (1) via the vacuum pipeline. The forepump (10), the vacuum valve, and the vacuum gauge are all located on the vacuum pipeline.

6. A process for a large-size lithium yttrium fluoride single crystal growth system, applied to the large-size lithium yttrium fluoride single crystal growth system according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Temperature field cleaning: Cleaning the furnace body and the equipment inside the furnace body; S2. Raw material pretreatment: The proportioned raw materials are loaded into the large crucible of the melting equipment for pre-melting. S3. Pre-melting process: Under high vacuum (below 8.0×10^-4 Pa), the temperature is raised to 250-300℃ while carbon tetrafluoride gas is introduced as the reaction gas; then argon gas is introduced into the furnace and the temperature is raised again until the raw material begins to melt; after the raw material is completely melted, the melt temperature is adjusted to 850-900℃ and held for 24 hours, then the temperature is lowered for 8-12 hours to room temperature; after pre-melting is completed, the raw material in the crucible is removed and weighed, and the amount of lithium fluoride volatilization is calculated; the black volatiles on the surface of the raw material are cleaned, and the lumpy raw material is broken into small pieces and stored in vacuum packaging bags; S4. Loading the furnace: Weigh an appropriate amount of pre-melted material, replenish the weight of the lithium fluoride lost by burning, and then load them together into the crucible. Load the furnace according to the normal operating sequence. After the furnace is closed, start to draw the furnace into low vacuum and high vacuum in sequence according to the process requirements. After the high vacuum reaches 3.0×10^-3Pa, start to raise the temperature to 250-300℃ and keep it constant for 12 hours. S5. Gas filling: Fill the furnace with high-purity argon (BIP grade) at a flow rate of 7L / min until the furnace pressure is -50 kPa to -60 kPa, then stop filling with argon; then fill the furnace with high-purity carbon tetrafluoride gas (above 5N) at a flow rate of 5L / min for 1-5s, then stop filling with argon. S6. Increase temperature: Set the temperature inside the crucible to 880℃ for 12 hours, and then maintain the temperature. S7. Melt treatment: After the raw material has completely melted, adjust the crucible position to the crystal-leading crucible position; set the crucible rotation speed from -20 rpm to +20 rpm, with an acceleration of 0.5 rpm / s; continue to maintain the temperature for 5 hours. S8. Seed crystal lowering: After 5 hours of constant temperature, set the crucible speed to +5 rpm for constant speed rotation, change the heater power to crystal pulling power, and set the seed crystal rod speed to 12-18 rpm; lower the seed crystal to 50 mm from the liquid surface at a speed of 10 mm / min, and hold for 10 minutes; then change the seed crystal rod pulling speed to 5 mm / min, lower it by 10 mm every 10 minutes until the bottom of the seed crystal is 1-5 mm from the liquid surface, and hold for 10 minutes. S9. Crystal introduction: Lower the seed crystal to the liquid surface to begin crystal introduction; Observe the solid-liquid interface state and the weight change displayed on the electronic scale; adjust the power to the seed crystal micro-melting, turn on the automatic growth control subsystem, and start automatic necking; set the seed crystal rod lifting rate to 0.5-1 mm / h, and set the second graphite cover plate lifting speed to 0.6-0.8 times the seed crystal rod speed, and move it upward synchronously; set the crystal diameter to gradually increase to the seed crystal size after lifting 3-5 mm; set the shoulder angle of the automatic growth control subsystem to gradually increase from 30° at the time of crystal pulling to 60° at the time of shoulder turning, set the crystal diameter of the constant diameter stage to gradually decrease from 52 mm to 50 mm, and the constant diameter length to 120-150 mm; set the parameters in the automatic growth control subsystem such as the crystal length of each stage, calculate and set the crucible lifting speed to ensure constant liquid level growth; S10. Cooling: After the crystal has grown to the target size or weight, shut down the automatic growth control subsystem and cool the furnace at a rate of 10-11.5℃ / h. S11. Furnace dismantling: After the crystal temperature drops to room temperature, remove the crucible from the furnace to take out the crystal, clean the furnace body and inside the furnace, and prepare for the next batch of crystal growth.

7. The process for growing large-size lithium yttrium fluoride single crystals according to claim 6, characterized in that: In S1, a vacuum cleaner and a lint-free cloth are used to clean the furnace body and the equipment inside the furnace.

8. The process for growing large-size lithium yttrium fluoride single crystals according to claim 6, characterized in that: In S2, the raw materials (with a purity of 4N) required for 9-10 heats of crystal growth are weighed and pre-melted.

9. The process for growing large-size lithium yttrium fluoride single crystals according to claim 6, characterized in that: In S7, when adjusting the crucible position to the crystal-leading crucible position, ensure that the melt surface is 5-10 mm away from the top of the heating zone.

10. The process for growing large-size lithium yttrium fluoride single crystals according to claim 6, characterized in that: In S4, the seed crystal head needs to be lowered to 100-150mm below the first graphite cover plate.

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