A temperature-controllable field structure for growing large-size low-temperature phase barium metaborate crystals

Abstract

The utility model provides a kind of controllable temperature field structure of large size low temperature phase barium metaborate crystal growth, solve the gradient heat demand in the process of BBO crystal growth that traditional fixed heat field cannot satisfy, its main scheme includes: furnace body and BBO seed crystal, the cavity is opened in the furnace body to place has crucible, the melt is built-in in the crucible, the BBO seed crystal is placed in the melt, and its top is connected to furnace body outside by vertical seed crystal stem, the inner wall of furnace body is fixed with two groups of heating elements on the corresponding BBO seed crystal place symmetrical formula, two groups of the heating element is symmetrical with the BBO seed crystal as center in height axial direction, and temperature measuring couple is set in the interval center between two to measure the temperature of inner cavity, the water cooling coil is also provided on the outside of corresponding heating element of furnace body, and the water cooling coil center height corresponds with the BBO seed crystal.

Description

Technical Field

[0001] This invention relates to the field of crystal growth technology, and in particular to a controllable temperature field structure for growing large-size low-temperature phase barium borate crystals. Background Technology

[0002] Barium metaborate crystal (BBO crystal) is a novel ultraviolet frequency doubling crystal, widely used in laser frequency doubling, frequency mixing, optical parametric oscillators, etc., and has become one of the core materials in the field of modern nonlinear optics technology.

[0003] However, stable growth of large-size BBO crystals remains a technical challenge. There are various methods for growing β-BBO crystals, such as the Czochralski method, the Laser Heated Pile Method (LHPG), and the Moving Zone Melting (TSZM). The Top Seed Method (TSSG) is currently the best method for growing large-size, high-quality β-BBO crystals. The flux chosen in the Top Seed Method is crucial. An ideal flux should possess low viscosity, low volatility, and high solubility.

[0004] at present and Flux is the most typical flux for growing β-BBO. When selecting... When used as a flux, the viscosity of the melt gradually increases as the crystal grows, leading to a slowdown in mass transfer. Furthermore, the increased melt viscosity and slowed mass transfer can cause component supercooling, and the already grown BBO crystals act as a shield for the melt, further weakening convection and removing heat from the crystallization interface.

[0005] In traditional axisymmetric crystal growth methods, an externally fixed thermal field is established, characterized by specific axial and radial temperature gradients. However, under the action of this symmetrical steady-state thermal field, the convective flow of the melt in the cylindrical crucible is affected by symmetry / asymmetry and vertical gravitational differentiation.

[0006] To address these issues, we propose a controllable temperature field structure for growing large-size, low-temperature barium metaborate crystals. Utility Model Content

[0007] The technical problem to be solved by this invention is to overcome the defects of the existing technology. This invention proposes a controllable temperature field structure for growing large-size low-temperature phase barium borate crystals. By designing two large groups of heating resistance wires, each of which is composed of three small groups of heating resistance wires, a temperature field that conforms to the growth of BBO crystals is established. Each group of heating resistance wires can achieve individual temperature control.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is: a controllable temperature field structure for growing large-size low-temperature phase barium borate crystals, including: a furnace body and a BBO seed crystal. The furnace body has a cavity for placing a crucible. The crucible contains a melt. The BBO seed crystal is placed in the melt, and its top is connected to the outside of the furnace body through a vertical seed crystal rod. The furnace body has two sets of heating elements symmetrically fixed on the inner wall at the corresponding BBO seed crystal. The two sets of heating elements are symmetrical about the BBO seed crystal in the height axis, and a thermocouple is set at the center of the interval between them to measure the temperature of the inner cavity. The furnace body also has a water-cooled coil on the outside of the corresponding heating element. The center height of the water-cooled coil corresponds to the BBO seed crystal.

[0009] Furthermore, each of the heating elements includes an outer insulation layer, a resistance wire, and an inner insulation layer. The outer insulation layer and the inner insulation layer seal the resistance wire into an integral annular structure, and the corresponding annular structure is coaxially arranged on the outside of the crucible.

[0010] Furthermore, the resistance wire comprises at least three groups and is equidistantly surrounded by the crucible, and the height of the resistance wire is not less than half the height of the crucible.

[0011] Furthermore, the water-cooled coil is circulated with externally connected condensate, which is also a ring structure and located outside the heating element.

[0012] Furthermore, the furnace body material includes one or more of the following: zirconia insulating bricks, alumina insulating bricks, zirconia microsphere insulating bricks, and alumina microsphere insulating bricks.

[0013] Furthermore, the top of the furnace body is provided with observation windows, including at least two observation windows symmetrical to the seed crystal rod, each observation window is inclined and communicates with the inner cavity of the furnace body, and its top is sealed by a quartz cover.

[0014] Furthermore, the heating element is integrated with an external electronic control unit for temperature control accuracy not exceeding ±0.01°C.

[0015] Furthermore, the condensate flow rate fluctuation within the water-cooled coil is ≤±0.5%.

[0016] Compared with existing technologies, the beneficial effects of this invention include: by controlling two symmetrical heating elements and the corresponding condensation temperature, the temperature can be controlled in three different states, allowing melt convection to satisfy the symmetry of the trigonal BBO crystal system, forming three flow lines on the melt surface that converge at the cold point. This structure allows the cold point to be offset from the center of the seed crystal and the grown crystal, avoiding inclusions in the middle part caused by the central region of the crystal coinciding with the center of the cold point, resulting in a near-zero flow velocity in the central region. Attached Figure Description

[0017] The disclosure of this utility model is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this utility model. In the drawings, the same reference numerals are used to refer to the same parts. Wherein: Figure 1 The schematic diagram shows a schematic representation of the internal structure of a furnace body according to one embodiment of the present invention; Figure 2 The schematic diagram shows a schematic view of the axial cross-sectional structure of a heating element according to one embodiment of the present invention.

[0018] The following are the labels in the diagram: 1. Quartz cover plate; 2. Seed crystal rod; 3. Observation window; 4. Heating element; 401. Inner insulation layer; 402. Resistance wire; 403. Outer insulation layer; 5. BBO seed crystal; 6. BBO crystal; 7. Furnace body; 8. Crucible; 9. Melt; 10. Thermocouple; 11. Water-cooled coil. Detailed Implementation

[0019] It is readily understood that, based on the technical solution of this utility model, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of this utility model. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative descriptions of the technical solution of this utility model and should not be considered as the entirety of this utility model or as limitations or restrictions on the technical solution of this utility model.

[0020] According to one embodiment of the present invention, in conjunction with Figures 1-2 As shown.

[0021] like Figure 1 As shown, in this embodiment, a controllable temperature field structure for growing large-size low-temperature barium borate crystals includes: a furnace body and a BBO seed crystal. The furnace body has a cavity for placing a crucible, and the crucible contains a melt. The BBO seed crystal is placed in the melt, and its top is connected to the outside of the furnace body through a vertical seed crystal rod. The furnace body has two sets of heating elements symmetrically fixed on the inner wall at the corresponding BBO seed crystal. The two sets of heating elements are symmetrical about the BBO seed crystal in the height axis, and a thermocouple is set at the center of the interval between them to measure the temperature of the inner cavity. The furnace body also has a water-cooled coil on the outside of the corresponding heating element, and the center height of the water-cooled coil corresponds to the BBO seed crystal.

[0022] like Figure 2As shown, each heating element includes an outer insulation layer, a resistance wire, and an inner insulation layer. The outer insulation layer and the inner insulation layer seal the resistance wire into an integral annular structure, and the corresponding annular structure is coaxially arranged on the outside of the crucible.

[0023] Furthermore, the resistance wire comprises at least three sets and is equidistantly wrapped around the crucible, with the height of the resistance wire being no less than half the height of the crucible. The water-cooled coil circulates with externally connected condensate, also having a ring structure and positioned outside the heating element. The furnace body material includes one or more of zirconia insulating bricks, alumina insulating bricks, zirconia microsphere insulating bricks, and alumina microsphere insulating bricks. An observation window is provided on the top of the furnace body, comprising at least two windows symmetrically positioned opposite the seed crystal rod. Each observation window is inclined and communicates with the inner cavity of the furnace body, and its top is sealed with a quartz cover.

[0024] As can be seen from the above structure, in order to avoid the influence of the traditional axially fixed external thermal field on the symmetry / asymmetry of the convective flow of the melt in the crucible and the vertical gravitational differentiation, according to Curie's principle, under the action of an external thermal field with a certain symmetry, convection can form a corresponding symmetrical flow. Since BBO crystal belongs to the trigonal crystal system, this invention establishes a temperature field that conforms to the growth of BBO crystal by designing two symmetrical heating elements, one above the other. The heating resistance wire in each set of heating elements can achieve individual temperature control.

[0025] Thus, thermal convection forms flow lines on the surface of the melt, and the intersection of these flow lines is what is known as the "cold spot" in crystal growth.

[0026] The axial temperature gradient is increased by using two sets of heating resistance wires, and the radial temperature gradient is increased by adding a water-cooling coil on the outside of the heating element. Combined with an external integrated electronic control, the temperature of the heating element and the water flow rate are precisely controlled, with a temperature control accuracy better than ±0.01°C and a water cooling flow rate fluctuation ≤±0.5%.

[0027] By controlling three sets of equidistantly arranged resistance wires in the heating element, the furnace cavity temperature can be controlled in three different states, allowing melt convection to satisfy the symmetry of the trigonal BBO crystal system. This results in three flow lines forming on the melt surface and converging at the cold point. This structure allows the cold point to be offset from the center of the seed crystal and the grown crystal, avoiding inclusions in the middle section caused by the central region of the crystal coinciding with the center of the cold point, resulting in a near-zero flow velocity in the central region.

[0028] The technical scope of this utility model is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this utility model, and all such modifications and variations should fall within the protection scope of this utility model.

Claims

1. A controllable temperature field structure for growing large-size, low-temperature phase barium metaborate crystals, characterized in that, include: The furnace body and the BBO seed crystal are described. The furnace body has a cavity for placing a crucible, and the crucible contains melt. The BBO seed crystal is placed in the melt, and its top is connected to the outside of the furnace body through a vertical seed crystal rod. The furnace body has two sets of heating elements fixed symmetrically on the inner wall at the corresponding BBO seed crystal. The two sets of heating elements are symmetrical about the BBO seed crystal in the height axis, and a thermocouple is set at the center of the interval between them to measure the temperature of the inner cavity. The furnace body also has a water-cooled coil on the outside of the corresponding heating element, and the center height of the water-cooled coil corresponds to the BBO seed crystal.

2. The controllable temperature field structure for growing large-size low-temperature phase barium metaborate crystals according to claim 1, characterized in that: Each heating element includes an outer insulation layer, a resistance wire, and an inner insulation layer. The outer insulation layer and the inner insulation layer seal the resistance wire into an integral annular structure, and the corresponding annular structure is coaxially arranged on the outside of the crucible.

3. The controllable temperature field structure for growing large-size low-temperature phase barium metaborate crystals according to claim 2, characterized in that: The resistance wire comprises at least three groups and is equidistantly surrounded by the crucible, and the height of the resistance wire is not less than half the height of the crucible.

4. The controllable temperature field structure for growing large-size low-temperature phase barium metaborate crystals according to claim 1, characterized in that: The water-cooled coil is internally circulated with externally connected condensate, which is also a ring structure and located outside the heating element.

5. The controllable temperature field structure for growing large-size low-temperature phase barium metaborate crystals according to claim 1, characterized in that: The top of the furnace body is provided with an observation window, which includes at least two windows symmetrical to the seed crystal rod. Each observation window is inclined and communicates with the inner cavity of the furnace body, and its top is sealed by a quartz cover.

6. The controllable temperature field structure for growing large-size low-temperature phase barium metaborate crystals according to claim 1, characterized in that: The heating element is integrated with an external electronic control unit for temperature control, with a temperature control accuracy of no more than ±0.01°C.

7. The controllable temperature field structure for growing large-size low-temperature phase barium metaborate crystals according to claim 4, characterized in that: The condensate flow rate fluctuation in the water-cooled coil is ≤ ±0.5%.

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