A method for preparing composite crystal

Abstract

The present invention relates to a method for preparing a composite crystal, comprising: providing a crucible, the shape of which matches the preset shape of the composite crystal; arranging a seed crystal for growing the crystal at one end of the crucible; arranging a matrix raw material and a doping raw material for growing the crystal in the crucible according to the step-by-step situation of the matrix crystal and the doping crystal in the composite crystal; placing the crucible horizontally, heating the crucible, so that the raw material in the crucible starts to melt from the end where the seed crystal is arranged, and the rest of the raw material remains in an unmelted state; and moving the crucible horizontally, so that the region where the raw material in the crucible is melted gradually moves from one end of the seed crystal to the other end until the crystal growth is completed. The method for preparing the composite crystal of the present invention has low cost, convenient observation, high crystal utilization, and can directly grow a complete and high-quality large-sized composite crystal.

Description

Technical Field

[0001] The invention relates to the field of crystal preparation, and in particular to a method for preparing a composite crystal. Background Art

[0002] Yttrium aluminate (YAlO3, YAP) laser crystals doped with rare earth ions as active ions are widely used in solid-state lasers due to their ability to directly output linearly polarized lasers, high conversion efficiency, and good mechanical and thermal properties. At present, undoped pure matrix crystals are usually compounded at both ends of the laser crystals doped with active ions to effectively improve the heat dissipation performance of the laser crystals, reduce the thermal effects of the laser crystals, and improve the output power level and beam quality of the solid-state lasers.

[0003] In the related art, there are three main methods for manufacturing composite crystals, namely, photobonding, bonding and thermal diffusion bonding.

[0004] The optical bonding method is a common method for preparing composite gain media for low-power lasers. The steps of the preparation process are: optical precision machining of the bonding surface, chemical cleaning and activation of the bonding surface, and optical bonding. However, the composite laser crystal prepared by the optical bonding method has very low strength and cannot meet the requirements of high-power laser use.

[0005] The bonding method is used to prepare composite laser crystals. This method is to coat a layer of optical adhesive such as UV curing adhesive on the surface that has been precisely processed optically, and then use the adhesive to bond two crystals together. It is usually used as a composite between heterogeneous materials for low-power lasers. The composite laser crystals prepared by this method have large optical losses and are easily damaged by high-power lasers, so they are not suitable for high-power laser applications.

[0006] Thermal diffusion bonding is also called glue-free thermal bonding method, which is divided into low temperature and high temperature according to the thermal bonding temperature. However, regardless of low temperature or high temperature, it generally goes through four processes, namely optical precision machining of the bonding surface, chemical cleaning and activation of the bonding surface, optical glue connection and thermal bonding. The bonded laser crystal prepared by this method has low optical loss and high strength on the bonding surface, which is suitable for the use requirements of various low, medium and high power levels of solid lasers. However, the thermal diffusion bonding method is suitable for cubic crystals such as YAG because they are isotropic; if thermal diffusion bonding technology is used to prepare anisotropic laser crystals such as YLF and YAP, lattice mismatch of the bonding surface is likely to occur during the thermal bonding process, resulting in large loss of the bonding surface; or the bonding strength of the bonded crystal is low, and due to the influence of the anisotropy of the thermal expansion coefficient, there is a risk of detachment when used at high power. It is difficult to prepare YLF composite crystals and YAP composite laser crystals with high composite strength and low loss using the thermal diffusion bonding process.

[0007] In addition, for the other crystal preparation methods, the optical floating zone method for growing composite laser crystals has the problem that the size of the prepared laser crystals is limited by the growth method, and large-sized, high-quality laser crystals cannot be obtained; and the preparation method using the pulling method to directly grow composite crystals also has the problems of long growth cycle and easy cracking of the crystals.

[0008] That is, the crystal preparation method in the related art is difficult to directly prepare large-sized and high-quality composite crystals. Summary of the invention

[0009] The purpose of the present invention is to provide a method for preparing a composite crystal to solve the problem that it is difficult to prepare a large-sized and high-quality composite crystal.

[0010] The preparation method of the composite crystal of the present invention comprises:

[0011] Providing a crucible, the shape of the crucible matches the preset shape of the composite crystal;

[0012] A seed crystal for growing crystals is arranged at one end of the crucible;

[0013] According to the separation of the matrix crystal and the doped crystal in the composite crystal, a matrix raw material and a doped raw material for growing the crystal are arranged in the crucible;

[0014] Placing the crucible horizontally, and heating the crucible so that the raw materials in the crucible begin to melt from the end where the seed crystal is arranged, and the rest of the raw materials remain in an unmelted state;

[0015] The crucible is moved horizontally so that the region where the raw material is melted in the crucible gradually moves from one end of the seed crystal to the other end until the crystal growth is completed.

[0016] Optionally, the crucible includes a seed crystal chamber, a shoulder area and a constant diameter area in sequence;

[0017] The seed crystal chamber is used to place the seed crystal;

[0018] The diameter of the shoulder area gradually increases from a position close to the seed crystal chamber to a position far away from the seed crystal chamber;

[0019] The equal diameter areas have equal diameters.

[0020] Optionally, the matrix material and the doping material fill the shoulder area and the equal-diameter area according to corresponding distribution conditions.

[0021] Optionally, the composite crystal is a composite laser crystal.

[0022] Optionally, the matrix raw material includes any one of YLF crystal raw material, YAP crystal raw material, YVO4 crystal raw material and YAG crystal raw material; the doping raw material is doped with at least one of Nd, Tm, Ho, Yb, Er, Pr and Ce on the basis of the matrix raw material.

[0023] Optionally, according to the step-by-step situation of the matrix crystal and the doped crystal in the composite crystal, the matrix raw material and the doped raw material for growing the crystal arranged in the crucible include any one of the following:

[0024] The composite crystal is a single-ended composite crystal, and a matrix raw material and a doping raw material are sequentially arranged in the crucible;

[0025] The composite crystal is a double-ended composite crystal, and a matrix raw material, a doping raw material and a matrix raw material are sequentially arranged in the crucible.

[0026] Optionally, the speed of horizontally moving the crucible ranges from 5 mm / h to 10 mm / h.

[0027] Optionally, the crucible is a boat-type crucible.

[0028] Optionally, placing the crucible horizontally and heating the crucible comprises:

[0029] Placing the crucible horizontally in the furnace;

[0030] The furnace is sealed and evacuated until the pressure in the furnace reaches 1×10 -4 Below Pa;

[0031] The crucible is heated to a temperature at which the raw material in the crucible can be melted.

[0032] Optionally, after heating the crucible to a temperature capable of melting the raw materials in the crucible and before horizontally moving the crucible, the step further includes: maintaining a constant temperature in the furnace within a set time, wherein the set time is greater than 1 hour.

[0033] The method for preparing the composite crystal of the present invention is to arrange the raw materials in a crucible according to the structure of the composite crystal, and gradually move the crucible so that the raw materials in the crucible gradually melt and solidify along one end of the seed crystal toward the other end. The method for preparing the composite crystal introduces a heat treatment process, and the prepared composite crystal has high strength and is suitable for high-power operation. There is a continuous lattice structure between the growth interfaces, and no additional adhesive is required, and the optical loss is small. In addition, the growth of the crystal is achieved by gradually melting and solidifying the raw materials, so there is no extremely high requirement for lattice mismatch and thermal expansion difference when splicing two crystals prepared in advance. The requirements for the process are relatively simple, and there is a continuous lattice structure between the growth interfaces, and the applicability is relatively high. In addition, the method for preparing the composite crystal of the present invention is low in cost, convenient for observation, and high in crystal utilization. The continuous growth of composite crystals is achieved, and the growth interfaces are continuous lattice structures with high strength and low depolarization loss. Complete large-sized composite crystals can be directly grown, reducing the risk of cracking caused by large differences in thermal expansion coefficients of various crystal directions during the growth of large-sized anisotropic crystals. The growth time is also reduced, and the yield and efficiency of composite crystal preparation are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the basic process of the crystal preparation method of this embodiment;

[0035] Figure 2 Schematic diagram of melting of raw materials in the crystal preparation method of this embodiment;

[0036] Figure 3 is a schematic diagram of the structure of the crucible and the raw materials filled therein in the crystal preparation method of this embodiment;

[0037] Figure 4 Detailed schematic diagram of the crystal preparation method of this embodiment;

[0038] 1-crucible; 2-seed crystal; 3-matrix raw material; 4-doping raw material; 5-area where raw material is melted; 6-seed crystal chamber; 7-shoulder area; 8-equal diameter area. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0040] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0041] Embodiment 1:

[0042] In order to prepare a large-sized and high-quality composite crystal, this embodiment provides a method for preparing a composite crystal, see Figure 1 As shown, it includes but is not limited to the following steps:

[0043] S101, providing a crucible, the shape of the crucible matches the preset shape of the composite crystal;

[0044] Crucible 1 is a vessel for melting metal or other substances. In this embodiment, it is used to hold and melt the raw materials of the composite crystal, and can be made of materials that can be used for crystal growth, including but not limited to quartz, boron nitride, platinum or iridium. The preset shape of the composite crystal is the desired shape of the composite crystal after growth. Since the preparation method of the composite crystal in this embodiment will melt and solidify the raw materials required for growing the crystal in the crucible 1. Therefore, the shape of the crucible 1 will be set according to the desired shape of the composite crystal, so that the desired shape is directly formed after the raw materials are melted and solidified.

[0045] S102, setting a seed crystal for growing crystals at one end of the crucible;

[0046] The seed crystal 2 is a small crystal having the same crystal orientation as the composite crystal, and is a seed for growing a single crystal, and can also be called a crystal seed. Using the seed crystal 2 as a growth seed can provide guidance and control for the growth direction and structure of the formed crystal, and ensure the quality of growth.

[0047] S103, according to the separation of the matrix crystal and the doped crystal in the composite crystal, placing a matrix raw material and a doped raw material for growing the crystal in a crucible;

[0048] The preparation method of this embodiment is used to grow a composite crystal, and the raw materials for growing the composite crystal include a matrix raw material 3 and a doping raw material 4. The composite crystal includes two parts: a matrix crystal and a doping crystal. The matrix crystal (or pure matrix crystal) is a non-gain medium layer, in which rare earth elements are not doped. The matrix raw material 3 of this embodiment is a raw material for forming a matrix crystal. The doped crystal is a gain medium layer, in which a part of rare earth elements are doped. The doping raw material 4 of this embodiment is a raw material for forming a doped crystal.

[0049] The arrangement order and proportion of the matrix material 3 and the doping material 4 are based on the step-by-step conditions of the matrix crystal and the doping crystal in the composite crystal, so as to directly prepare the desired composite crystal.

[0050] S104, placing the crucible horizontally, and heating the crucible so that the raw materials in the crucible begin to melt from the end where the seed crystal is arranged, and the rest of the raw materials remain in an unmelted state;

[0051] That is, in this embodiment, the raw material in the crucible 1 is partially melted, and the melting starts from the seed crystal 2. Of course, the rest of the raw material can also be in a heated state, but not to the melting level.

[0052] S105, moving the crucible horizontally so that the region where the raw material is melted in the crucible gradually moves from one end of the seed crystal to the other end until the crystal growth is completed;

[0053] It should be noted that the raw materials referred to in the present application are a general term for the matrix raw material 3 and the doping raw material 4, and do not refer to a specific one of them. In the process of moving the crucible 1, based on the position of the crucible 1 and the temperature distribution in the environment, the melted raw material can be one of the matrix raw material 3 and the doping raw material 4; and when the raw material melting area 5 is at the critical point of the two raw materials, the matrix raw material 3 and the doping raw material 4 will be melted at the same time.

[0054] like Figure 2 As shown, the raw material melting area 5 gradually moves from one end of the seed crystal 2 to the other end, and finally all the raw materials in the crucible 1 will complete the melting and solidification process. In this process, the melt at the end of the crucible 1 close to the seed crystal 2 gradually solidifies into a single crystal as the crucible 1 moves, while the raw material at the end far from the seed crystal 2 is gradually melted as the crucible 1 moves, realizing a continuous crystal growth process.

[0055] The method for preparing the composite crystal of the present embodiment is to arrange the raw materials in the crucible 1 according to the structure of the composite crystal, and gradually move the crucible 1 so that the raw materials in the crucible 1 gradually melt and solidify along one end of the seed crystal 2 toward the other end. The method of the present embodiment introduces the process of heat treatment, and the prepared composite crystal has high strength and is suitable for the needs of high-power operation. There is a continuous lattice structure between the growth interfaces, and no additional adhesive is required, and the optical loss is small. In addition, the present embodiment realizes the growth of the crystal by the gradual melting and solidification of the raw materials, so there is no extremely high requirement for lattice mismatch and thermal expansion difference when splicing two crystals prepared in advance, the requirements for the process are relatively simple, and there is a continuous lattice structure between the growth interfaces, and the applicability is relatively high. The method for preparing the composite crystal of the present embodiment is low in cost, convenient for observation, and high in crystal utilization. It can be seen that the composite crystal preparation method of this embodiment realizes the continuous growth of composite crystals, and the growth interfaces are continuous lattice structures with high strength and small depolarization loss; and can directly grow complete large-sized composite crystals, reducing the risk of cracking caused by large differences in thermal expansion coefficients of various crystal directions during the growth of large-sized anisotropic crystals, while also reducing the growth time and improving the yield and efficiency of composite crystal preparation.

[0056] As an example of a preset shape of a composite crystal, the composite crystal may include a seeding section, a shoulder section, and an equal diameter section. The seeding section is the part that grows from the seed crystal 2, and the shoulder section is between the seeding section and the equal diameter section. From the seeding section to the equal diameter section, the diameter of the shoulder section gradually increases to achieve a smooth transition. The equal diameter section is an area with equal diameters. Of course, in the actual production process, due to errors, they are usually not strictly equal.

[0057] In some embodiments, Figure 3 , corresponding to the preset shape of the composite crystal, the crucible 1 includes a seed crystal chamber 6, a shoulder area 7 and an equal diameter area 8 in sequence. The seed crystal chamber 6 is used to place the seed crystal 2; the diameter of the shoulder area 7 gradually increases from the position close to the seed crystal chamber 6 to the position away from the seed crystal chamber 6; the diameter of the equal diameter area 8 is equal. It can be understood that the above-mentioned seed crystal chamber 6, shoulder area 7 and equal diameter area 8 correspond to the seeding section, shoulder section and equal diameter section of the composite crystal respectively. In other embodiments, the preset shape of the composite crystal may also include other structures, and accordingly, it is only necessary to configure the interior of the crucible 1 to a corresponding shape. In this embodiment, the seed crystal chamber 6, shoulder area 7 and equal diameter area 8 are formed in the crucible 1 to produce a composite crystal, so that the composite crystal still has stages such as seeding, shouldering and equal diameter growth during the growth process, and can slowly enlarge the diameter from the vicinity of the seed crystal 2 to form a gradual transition growth, and the growth quality is good.

[0058] In some embodiments, the matrix material 3 and the doping material 4 fill the shoulder area 7 and the equal-diameter area 8 according to corresponding distribution conditions.

[0059] In some embodiments, the composite crystal may be a laser composite crystal. In other embodiments, the composite crystal may also be a composite crystal for other purposes.

[0060] Exemplarily, the matrix raw material 3 of this embodiment includes any one of YLF (yttrium lithium fluoride) crystal raw material, YAP (yttrium aluminate) crystal raw material, YVO4 (yttrium vanadate) crystal raw material and YAG (yttrium aluminum garnet) crystal raw material. The doping raw material 4 is doped with at least one rare earth element on the basis of the matrix raw material 3, such as at least one of Nd, Tm, Ho, Yb, Er, Pr, and Ce, that is, any one of them can be doped, or several of them can be doped. The preparation method of the composite crystal of this embodiment can be used not only to prepare anisotropic composite laser crystals such as YLF and YAP, but also to prepare isotropic composite laser crystals such as YVO4 and YAG, such as YVO4 and Re:YVO4 composite crystal (representing YVO4 crystal doped with element Re, where Re refers to rare earth element). Specifically, for anisotropic composite laser crystals, the preparation method can be used to grow single-ended composite laser crystals, such as single-ended composite YLF laser crystals: YLF / Nd:YLF, YLF / Tm:YLF, YLF / Ho:YLF, YLF / Pr:YLF, YLF / Ho:Tm:YLF, YLF / Er:YLF; single-ended composite YAP laser crystals: YAP / Nd:YAP, YAP / Tm:YAP, YAP / Ho:YAP, YAP / Pr:YAP, YAP / Ho:Tm:YAP.

[0061] According to the separation of the matrix crystal and the doped crystal in the composite crystal, the matrix raw material 3 and the doped raw material 4 for growing the crystal arranged in the crucible 1 include any of the following:

[0062] Case 1: The composite crystal is a single-ended composite crystal, and a matrix raw material 3 and a doping raw material 4 are sequentially arranged in a crucible 1 .

[0063] Case 2: The composite crystal is a double-ended composite crystal, and the matrix raw material 3 , the doping raw material 4 and the matrix raw material 3 are sequentially arranged in the crucible 1 .

[0064] The preparation method of the composite crystal of this embodiment is applicable to both single-terminal composite crystals and double-terminal composite crystals. It can be understood that, whether it is a single-terminal composite crystal or a double-terminal composite crystal, the raw materials in the crucible 1 can be configured according to the step-by-step situation of the matrix crystal and the doped crystal in the composite crystal, which is simple to operate and has good applicability.

[0065] As an example, Figure 2 or Figure 3As shown, the composite crystal to be grown is a double-ended composite crystal, exemplarily a YAP / Tm:YAP / YAP composite crystal. Starting from one end of the seed crystal 2, there are YAP crystal, Tm:YAP crystal and YAP crystal in sequence. Then, in the crucible 1, the shoulder area 7 near the seed crystal chamber 6 and a part of the equal-diameter area 8 are filled with the raw material of YAP crystal (matrix raw material 3), the raw material of YAP crystal doped with Tm element (dopant raw material 4) is filled near the middle of the equal-diameter area 8, and the raw material of YAP crystal (matrix raw material 3) is filled at one end of the equal-diameter area 8 away from the seed crystal chamber 6; the distribution of these raw materials in the crucible 1 is consistent with the structural distribution of the composite crystal itself, so that large-sized composite crystals can be directly formed.

[0066] In some embodiments, the speed of horizontally moving the crucible 1 ranges from 5 mm / h to 10 mm / h, for example, 6 mm / h, 8 mm / h, etc. The crucible 1 is slowly moved so that the raw materials in the corresponding area can be fully melted to ensure the smooth growth of the crystal. In some embodiments, the crucible 1 is a boat-type crucible.

[0067] like Figure 4 As shown, in some embodiments, the crucible 1 is placed horizontally, and heating the crucible 1 includes:

[0068] S201, placing the crucible horizontally in the furnace;

[0069] S202, seal the furnace and evacuate the furnace until the pressure inside the furnace reaches 1×10 -4 Below Pa;

[0070] S203, heating the crucible to a temperature capable of melting the raw materials in the crucible;

[0071] In some embodiments, after heating the crucible 1 to a temperature capable of melting the raw materials in the crucible 1 and before horizontally moving the crucible 1, the process further includes: maintaining the temperature in the furnace at a constant temperature for a set time, wherein the set time is greater than 1 hour. The constant temperature for several hours can stabilize the temperature field in the furnace and ensure the smooth growth of the composite crystal.

[0072] In order to better understand the preparation method of the composite crystal of the present application, this embodiment also describes a specific composite crystal growth process.

[0073] The equipment for growing composite crystals can be mainly composed of a furnace, a crystal receiving chamber, a vacuum system, an electric control system, etc. In this example, a boat-type crucible is used to grow a YAP / Tm:YAP / YAP composite crystal. The YAP / Tm:YAP / YAP composite crystal is a double-ended composite crystal, as described above. Figure 2 or Figure 3As shown, the crucible 1 comprises a seed chamber 6 , a shoulder region 7 and a constant diameter region 8 .

[0074] In this example, the seed crystal 2 can be selected from the b-axis YAP crystal, and its diameter is 4mm. The length of the shoulder area 7 is 20mm, and the length of the equal-diameter area 8 is 95mm. YAP and Tm:YAP crystal raw materials are prepared according to the chemical formula of YAP and Tm:YAP, the melt density and the volume of the crucible 1 occupied. Among them, the shoulder area 7 of the crucible 1 and the 25mm length of the equal-diameter area 8 close to the seed crystal chamber 6 are placed with YAP raw material; the middle 40mm length of the equal-diameter area 8 is placed with Tm:YAP raw material, and its doping concentration can be 0.2at% to 7at% (atomic percentage), for example, 2at%; the 30mm length of the equal-diameter area 8 away from the seed crystal chamber 6 is placed with YAP raw material.

[0075] Place the crucible 1 filled with raw materials into the middle of the furnace to see the hot air, seal it and evacuate it to 10 -4 Pa. Resistance heating is used to make the temperature at one end of the seed crystal chamber 6 reach 2000°C until the raw material melts, and the temperature is kept constant for several hours to stabilize the temperature field. Subsequently, the crucible 1 is moved horizontally at a speed of 5mm / h to 10mm / h to grow the crystal. In this process, the melt in the crucible 1 gradually solidifies into a single crystal as the crucible 1 moves, while the melt away from the seed crystal chamber 6 gradually melts as the crucible 1 moves, realizing a continuous crystal growth process based on the seed crystal 2.

[0076] The crystal growth process can be automatically controlled by a precision temperature program controller and an electronic control system according to preset parameters. After the crystal growth is completed, the furnace temperature is cooled to room temperature at a slow cooling rate (e.g., 20°C / h) to complete the growth of the YAP / Tm:YAP / YAP composite crystal.

[0077] In addition, although exemplary embodiments have been described herein, the scope includes any and all embodiments based on the present disclosure that are equivalent, modified, omitted, combined (e.g., various embodiments intersecting), adapted or changed. It is not limited to the examples described in this specification or during the implementation of the present invention, and its examples will be interpreted as non-exclusive.

[0078] The above description is intended to be illustrative rather than restrictive. For example, the above examples (or one or more of them) can be used in combination with each other. For example, those of ordinary skill in the art may use other embodiments when reading the above description.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a composite crystal, characterized in that: include: Providing a crucible, the shape of the crucible matches the preset shape of the composite crystal; A seed crystal for growing crystals is arranged at one end of the crucible; According to the separation of the matrix crystal and the doped crystal in the composite crystal, a matrix raw material and a doped raw material for growing the crystal are arranged in the crucible; Placing the crucible horizontally, and heating the crucible so that the raw materials in the crucible begin to melt from the end where the seed crystal is arranged, and the rest of the raw materials remain in an unmelted state; The crucible is moved horizontally so that the region where the raw material is melted in the crucible gradually moves from one end of the seed crystal to the other end until the crystal growth is completed.

2. The method for preparing a composite crystal according to claim 1, characterized in that: The crucible includes a seed crystal chamber, a shoulder area and a constant diameter area in sequence; The seed crystal chamber is used to place the seed crystal; The diameter of the shoulder area gradually increases from a position close to the seed crystal chamber to a position far away from the seed crystal chamber; The equal diameter areas have equal diameters.

3. The method for preparing a composite crystal according to claim 1, characterized in that: The matrix material and the doping material fill the shoulder area and the equal-diameter area according to corresponding distribution conditions.

4. The method for preparing a composite crystal according to claim 1, wherein: The composite crystal is a composite laser crystal.

5. The method for preparing a composite crystal according to claim 4, characterized in that: The matrix raw material includes any one of YLF crystal raw material, YAP crystal raw material, YVO4 crystal raw material and YAG crystal raw material; the doping raw material is doped with at least one of Nd, Tm, Ho, Yb, Er, Pr and Ce on the basis of the matrix raw material.

6. The method for preparing a composite crystal according to claim 4, characterized in that: According to the step-by-step situation of the matrix crystal and the doped crystal in the composite crystal, the matrix raw material and the doped raw material for growing the crystal arranged in the crucible include any one of the following: The composite crystal is a single-ended composite crystal, and a matrix raw material and a doping raw material are sequentially arranged in the crucible; The composite crystal is a double-ended composite crystal, and a matrix raw material, a doping raw material and a matrix raw material are sequentially arranged in the crucible.

7. The method for preparing a composite crystal according to claim 4, characterized in that: The speed of horizontally moving the crucible ranges from 5 mm / h to 10 mm / h.

8. The method for preparing a composite crystal according to claim 1, characterized in that: The crucible is a boat-type crucible.

9. The method for preparing a composite crystal according to any one of claims 1 to 8, characterized in that: Placing the crucible horizontally and heating the crucible comprises: Placing the crucible horizontally in the furnace; The furnace is sealed and evacuated until the pressure in the furnace reaches 1×10 -4 Below Pa; The crucible is heated to a temperature at which the raw material in the crucible can be melted.

10. The method for preparing a composite crystal according to claim 9, characterized in that: After heating the crucible to a temperature capable of melting the raw materials in the crucible and before horizontally moving the crucible, the method further includes: maintaining a constant temperature in the furnace within a set time, wherein the set time is greater than 1 hour.

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