A clean furnace device based on sealed bimetallic cavity to control the temperature of laser crystal

Abstract

The present invention relates to a clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity, comprising a front barrel, a furnace and a rear barrel coaxially assembled in sequence; the furnace is a cylindrical metal body with an L-shaped through hole in the axial direction, and the crystal is pressed and fixed in the L-shaped through hole by a stopper with a strain compensation spring; the front barrel and the rear barrel are metal cylinders with an axial through hole in the middle, one end of which is a window mirror end for installing a window mirror, and the other end has a first flange connection plate, called a furnace end, for connecting with the furnace, and is sealed by a furnace sealing ring to form a sealed inner clean cavity. By sealing the all-metal inner cavity, impurities such as water and particulate matter are not introduced, and gases such as fluoride are not generated. By sealing the metal outer cavity, the temperature fluctuation meets the requirements, and is used to control the temperature of cesium lithium borate and other laser crystals that have high requirements for the working environment.

Description

Technical Field

[0001] The invention relates to the field of laser crystal clean furnace devices, and in particular to a clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity. Background Art

[0002] All-solid-state UV lasers use the nonlinear effect of nonlinear crystals to perform frequency conversion to generate UV lasers. Nonlinear crystals are the most critical part in determining the output characteristics of all-solid-state UV lasers. They usually need to be maintained at a specific temperature during use, and have extremely high requirements for temperature fluctuation. 10 Compared with the commonly used nonlinear crystals β-BaB2O4 (BBO), LiB3O5 (CBO), etc., the crystal (CLBO) has the characteristics of wide ultraviolet light transmission band, high laser damage threshold, small discrete angle, high frequency doubling conversion efficiency, and easy growth into large-sized single crystals. It is very suitable for harmonics and ultraviolet sum frequency of Nd:YAG lasers, and can produce ultraviolet lasers with wavelengths of 355 nm, 266 nm, and 213 nm. It has extremely high industrialization potential in the field of all-solid-state ultraviolet laser manufacturing. However, in practical applications, CLBO crystals will deliquesce and crack when exposed to air. The higher the humidity, the faster the CLBO deliquesce and cracking phenomenon occurs. In the application scenarios of CLBO crystals, it is necessary to take advantage of the high laser damage threshold of CLBO crystals to increase the incident laser power and power density to increase the power of the output light. As the humidity increases, the laser damage threshold of CLBO decreases significantly. At the same time, under high-power density laser irradiation, micron-sized particles adhering to the surface of the crystal can cause crystal damage. These characteristics result in extremely demanding operating environments for CLBO crystals, greatly limiting their application in industrial production.

[0003] In terms of crystal temperature control, the current technical solutions mostly use mass-produced temperature controllers in combination with TEC ceramic cooling plates or resistance heating plates. The most important indicator is temperature fluctuation, which mainly depends on the structural design of the crystal heating seat. There are currently three methods for delaying the deliquescence of CLBO crystals: the first method is to place the CLBO crystal in a heating sleeve with both ends open and maintain the temperature above 100°C, which can delay the occurrence of deliquescence and cracking of the CLBO crystal. Generally, dry gas is required to blow and protect the exposed CLBO crystal end faces while ensuring that the particle level meets the standard. However, gas blowing accelerates convective heat dissipation, resulting in large temperature fluctuations of the crystal and unstable output beam quality; the second is to coat the CLBO crystal. One coating scheme is that silane coupling agents form a protective film on the crystal surface through chemical bonding. The current process is immature and the operation process is complicated. During the formation of the moisture-proof film, the crystal will still be in direct contact with water, which is an extremely expensive method; the third is to dope and modify the CLBO crystal. Generally, metal ions are doped into the crystal growth melt during the crystal growth process. Doping helps to improve the crystal's own deliquescence resistance, but different doping will cause different changes in the crystal properties. Therefore, crystal doping modification is more suitable as a means of customizing crystal properties. In terms of ensuring that the particle level meets the requirements, the current general approach is to build and use high-standard clean workshops to ensure that the CLBO crystal is in a high-cleanliness and low-humidity environment throughout its life cycle from the time of installation, which is costly.

[0004] Products of existing technology, such as the temperature-controlled furnace of Fujian Fujing Technology Co., Ltd., have a frequency-doubling crystal temperature fluctuation of 0.2°C (±0.1°C). The temperature fluctuation causes the Gaussian distribution, roundness, M-square and other indicators of the generated laser beam to fail to meet the requirements of a measurement light source, and can only be used as a light source for cutting, marking, cleaning, etc. As a detection light source, lasers have extremely high requirements for stability and consistency; therefore, the temperature fluctuation of the crystal must be less than 0.02°C (±0.01°C) to ensure that the quality of the generated laser can be used as a detection light source.

[0005] Therefore, a clean furnace device is needed that can fully isolate the influence of water vapor and accurately control the temperature of the laser crystal. Summary of the invention

[0006] The technical problem to be solved by the present invention is: in view of the current problems that CLBO crystals are easily deliquescent, have strict environmental requirements, resulting in extremely high use costs and are difficult to industrialize, a laser crystal clean furnace device is designed that has precise temperature control under large temperature differences, has a simple structure and is easy to manufacture, meets the requirements of the working environment but has extremely low use costs.

[0007] Compared with the related patents reported, the present invention designs an inner and outer double-layer metal cavity, constructs an inner clean cavity and an outer air cavity, the inner clean cavity can provide the clean conditions required for the laser crystal to work for a long time, and the outer air cavity can ensure that the temperature fluctuation of temperature control under large temperature difference conditions is extremely small. The structure of the present invention is simple and easy to manufacture, with low cost and reliable performance.

[0008] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0009] A clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetallic cavity, comprising a window mirror and a furnace, wherein the window mirror comprises a coaxially assembled front barrel and a rear barrel, and the structures of the front barrel and the rear barrel are the same; the furnace is a cylindrical metal body with good thermal conductivity and an L-shaped through hole in the axial direction, and the crystal is pressed and fixed in the L-shaped through hole by at least one limit block with a strain compensation spring, so as to achieve the goal of maintaining the working environment of the CLBO crystal at a low cost; the front barrel and the rear barrel are metal cylinders with a through hole in the middle, one end of which is called the window mirror end, and has a countersunk hole with an internal thread for installing the window mirror, and the other end has a first flange connection plate, called the furnace end, which is used to connect to the furnace and is sealed by a furnace sealing ring to form a sealed inner clean cavity; the middle part of the front barrel and the rear barrel also has a second flange connection plate; the inner clean cavity It is arranged in an external air cavity, and the external air cavity is formed by surrounding a front cover, a rear cover, a top cover and a base; the front cover and the rear cover are respectively connected to the second flanges of the front lens barrel and the rear lens barrel of the chamber, and an air barrier is provided between the inner clean cavity and the external air cavity; the window lens ends of the front lens barrel and the rear lens barrel of the chamber extend out of the front cover or the rear cover, and extend out of the external air cavity to ensure sufficient heat dissipation capacity; the outer cylindrical surface of the furnace chamber is provided with a countersunk hole, and the heating rod and the temperature probe are inserted into the furnace chamber through the countersunk hole, which are respectively used for heating the furnace chamber and measuring the furnace chamber temperature; it also includes a temperature controller for adjusting the heating power of the heating rod and detecting the temperature probe signal, the temperature controller is arranged outside the clean furnace, and the temperature controller is electrically connected to the heating rod and the temperature probe. This design isolates the external environment from the directly heated furnace chamber, fully isolates the influence of water vapor, and achieves the goal of extremely small temperature fluctuation of temperature control under large temperature difference conditions.

[0010] Furthermore, the window mirror ends of the front barrel and the rear barrel are sealed by metal sealing gaskets.

[0011] Furthermore, the window mirror is a lens coated with an anti-reflection film, and the window mirror ends of the front barrel and the rear barrel have internal threads. A window mirror fastening nut made of a metal ring with external threads cooperates with the internal threads to press the metal sealing gasket and the window mirror to form a sealed end face, thereby forming a sealed end face through which the laser can pass.

[0012] Furthermore, the metal sealing gasket is indium or indium alloy.

[0013] Furthermore, the furnace sealing ring is made of red copper; the limit block is made of red copper; the strain compensation spring is made of spring steel, has an M shape, and is made by a stamping process. During assembly at room temperature, the strain compensation spring is squeezed and compressed by the crystal, generating a resistance to press the crystal tightly and fix it in the L-shaped through hole of the furnace. When the temperature changes, the strain compensation spring absorbs the strain difference between the furnace and the crystal.

[0014] Furthermore, 6 countersunk holes are evenly distributed on the outer circumference of the furnace for installing a temperature probe and 5 heating rods. When the power of the heating rods changes, the furnace temperature can change in time and reach a steady state. The limit block with a strain compensation spring presses the crystal tightly and fixes it in the L-shaped through hole, and the furnace can quickly transfer heat to the crystal.

[0015] Furthermore, the temperature probe is a PT1000 temperature probe with a probe diameter of 4 mm and a length of 15 mm.

[0016] Furthermore, the heating rod is a stainless steel shell inner outlet type heating rod with a diameter of 4 mm and a length of 15 mm, and a power of 8W to 14W.

[0017] Furthermore, the insulation layer of the temperature probe wire and the signal wire or power wire of the heating rod is made of high temperature resistant glass wool.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention constructs a double-layer metal cavity, and the crystal is installed in the inner cavity. After installation, no water molecules, particulate matter, or gaseous impurities re-enter the inner cavity, thereby fully isolating the influence of water vapor.

[0020] 2. The outer cavity of the structure wraps the inner cavity and forms a gas insulation layer, achieving the goal of extremely small temperature fluctuation under high target temperature and low ambient temperature conditions.

[0021] 2. All parts are made of metal or high temperature resistant materials, which will not release particles at high temperatures and eliminate crystal contamination.

[0022] 3. Extend the service life of CLBO crystals and greatly reduce the use cost of CLBO crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic axial half-section view of a clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity according to the present invention;

[0024] Figure 2 It is a radial half-section schematic diagram of a clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity according to the present invention;

[0025] Figure 3 It is an exploded diagram of a clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity of the present invention;

[0026] Figure 4 It is a three-dimensional schematic diagram of a clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity of the present invention;

[0027] Figure 5 This is a schematic diagram of the product structure of the comparative example.

[0028] In the figure: 1-front barrel; 2-rear barrel; 3-furnace; 4-strain compensation spring; 5-limit block; 6-front cover; 7-rear cover; 8-top cover; 9-base; 10-crystal; 11-furnace sealing ring; 12-window mirror; 13-metal sealing gasket; 14-window mirror fastening nut; 15-temperature probe; 151 temperature probe wire; 16-heating rod; 161 heating rod wire. DETAILED DESCRIPTION

[0029] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0030] Crystal assembly and inner clean chamber assembly need to be carried out in a clean space. The crystal assembly and inner clean chamber assembly in this case are carried out in a negative pressure glove box with a volume of 600×450×420. Through the method of circulating purification and pumping negative pressure, the water oxygen value in the glove box is lower than 1PPM, and the cleanliness reaches the ISO1 cleanliness standard. During operation, the materials are first sent into the glove box, the air in the glove box is replaced with high-purity nitrogen, the purification cycle is turned on and vacuum is drawn, and the glove box can meet the environmental requirements for direct exposure of CLBO crystals. At this time, the assembly operation begins. In this embodiment, the material of the front barrel 1 and the rear barrel 2 is 2205 stainless steel, which has a very small thermal expansion coefficient and a relatively low thermal conductivity. The material of the furnace 3 is H96 brass, with a size of Ф20×14 (mm), the width of the middle L-shaped through hole is 5mm, the inner right angle is drilled to remove the rounded corners, and the outer right angle is chamfered to remove the sharp edges; the size of the crystal 10 is 5×5×12 (mm), the material of the limit block 5 is H96 brass, with a size of 5×4.8×12 (mm), the size of the pressing surface of the limit block 5 in contact with the crystal 10 is 4.8×12 (mm), and there is a larger groove opposite the pressing surface for installing the stamping forming The strain compensation spring 4 has a circular hole on each of the two end faces of the limit block 5; the strain compensation spring 4 is clamped on the limit block 5, and the two sets of limit blocks are sent into the L-shaped through hole of the furnace 3. At this time, a through hole with a net cross-sectional size less than 5×5 (mm) is formed. The circular holes at both ends of the limit block 5 are clamped with tools and the strain compensation spring 4 is compressed radially outward, so that the two sets of limit blocks 5 and the right-angled surfaces of the L-shaped through hole form a through hole with a net cross-sectional size greater than 5×5 (mm). After the crystal 10 is sent into the hole, the tool clamping the limit block 5 is released to release the strain compensation spring 4. The limit block 5 presses and fixes the crystal 10 from two directions perpendicular to each other. Then use the window mirror fastening nut 14 made of 316 stainless steel to lock the metal sealing gasket 13 and the window mirror 12 into the front mirror barrel 1 and the rear mirror barrel 2, and then use the furnace bolts and the furnace sealing ring 11 to lock and seal the front mirror barrel 1, the furnace 3 with the crystal installed, and the rear mirror barrel 2 to form a sealed inner clean chamber.

[0031] When the inner clean chamber is assembled, the glove box can be taken out as a whole. The inner clean chamber is completely sealed, contains no polymer materials, and no gaseous impurities evaporate under high temperature conditions, and no water molecules and particulate matter re-enter, so the internal clean state can be maintained for a long time.

[0032] Five stainless steel heating rods 16 with a voltage of 24V, a power of 8W and a size of Ф4×15 (mm) are coated with high-temperature resistant thermal conductive silicone on the surface and inserted into the countersunk hole on the outer cylindrical surface of the furnace 3. A PT1000 temperature probe 15 with a size of Ф4×15 (mm) is also coated with high-temperature resistant thermal conductive silicone and inserted into the countersunk hole on the outer cylindrical surface of the furnace 3. The lead insulation layer of the temperature probe 15 and the heating rod 16 is a high-temperature resistant glass fiber insulation layer.

[0033] The material of the front cover 6 and the rear cover 7 is 2205 stainless steel, and there is a Ф3.1 (mm) hole on the side. There are 6 bolt holes on the flanges located on the front barrel 1 and the rear barrel 2 for installing the front cover 6 and the rear cover 7, three in a group, a total of two groups, one group with a center angle of 60°, and the other group with a center angle of 55°, ensuring the uniqueness of this assembly.

[0034] The top cover 8 and the base 9 are made of 2205 stainless steel, and the inner surfaces are provided with grooves for wiring. After the temperature probe line 151 and the heating rod line 161 are combed, the top cover 8 and the base 9 cover the cylindrical surface formed by the front cover 6 and the rear cover 7, and are locked into the φ3.1 (mm) holes on the sides of the front cover 6 and the rear cover 7 with set screws. At this time, the front cover 6, the rear cover 7, the top cover 8 and the base 9 jointly form an outer air cavity with a partition. The temperature probe line 151 and the heating rod line 161 are completely separated from the furnace 3 by the partition formed by the front cover 6 and the rear cover 7, and are led out from the hole in the base 9, and the hole is blocked with a metal gland.

[0035] The temperature probe 15 and the heating rod 16 are connected to the temperature controller. In this embodiment, under the working conditions of the ambient temperature of 25°C and the target temperature value of 150°C, the steady state is achieved within 25 minutes, and the temperature control accuracy is that the temperature fluctuation is less than 0.02°C (±0.01°C).

[0036] The product of this embodiment is tested, and the process is as follows:

[0037] 1. Temperature fluctuation measurement, dedicated temperature controller, upper temperature limit

[0038] Using Xiafan Optoelectronics TCB-NE temperature controller, Sunny Precision Instrument SED96 series temperature controller, Yudian AIJ-5.0P temperature controller, and Yexian Technology TCM-M115 digital temperature control module, five 8W heating rods were installed in parallel, and with the PT1000 temperature probe, under the ambient temperature of 25±3℃, the temperature reached 150℃ in 30 minutes, the maximum temperature control was 200℃, and the steady-state temperature fluctuation was less than ±0.01℃ (temperature fluctuation was less than 0.02℃).

[0039] 2. CLBO crystal frequency doubling conversion stability.

[0040] A 30W 532nm laser with a spot diameter of 0.4mm was used to generate a 2.6W 266nm ultraviolet laser through a clean furnace of the present invention equipped with a CLBO crystal of size 5×5×12. The power fluctuation was ±0.1W and the power was not significantly attenuated after the oven was continuously heated for 30 days.

[0041] A conventional heating furnace, with the same input, generates 2.2W 266nm UV laser with a power fluctuation of ±0.5W. After 7 days of continuous baking, the power drops to 0.8W.

[0042] 3. High temperature produces gaseous impurities and particulate matter during use

[0043] The all-metal clean cavity does not have the theoretical conditions for generating gas, and the temperature is maintained at 180°C in the glove box environment (in the copper technology solution). The machine is baked for one week, and the gas inside the clean furnace is sampled. The fluoride in the gas is measured by the filter membrane sampling-fluoride ion selective electrode method. No gaseous fluoride is detected. The particulate matter is tested, and no particulate matter ≥0.3um is detected, which meets the ISO1 level proximity requirements.

[0044] 4. Can it absorb thermal expansion strain and prevent crystal cracking?

[0045] The CLBO crystal with optical defects was installed in this clean furnace, and five 12W heating rods were used to heat it from room temperature to 150 degrees in 10 minutes, and it was cooled to room temperature after about 40 minutes, and then heated to 150 degrees. The cycle was repeated 20 times, and the crystal was placed under a high-power microscope, and no cracks were detected. Using a commercially available heating furnace, cracks appeared in the crystal after 4 cycles.

[0046] 5. Crystal end temperature fluctuation

[0047] A defective and damaged CLBO crystal is used, and a patch temperature probe is attached to a local position of the crystal end face. When the temperature of the clean furnace of the present invention is controlled at 150° C., the end face temperature fluctuation of the present invention is less than 0.02° C.

[0048] The test results of the product of this embodiment and its performance comparison with the existing products are shown in Table 1. The product of this embodiment has the performance of maintaining a very small temperature fluctuation (0.02°C) for a long time. During the test, since the minimum measurement division of the temperature probe used is 0.01°C, it is not ruled out that the actual performance of the product design of this embodiment can achieve a smaller temperature fluctuation.

[0049] Table 1

[0050] Technical indicators significance Prior art The present invention Temperature fluctuation (℃) The smaller the temperature fluctuation, the more stable the frequency doubling conversion, the smaller the power fluctuation, and the better the output light pointing stability. When the temperature fluctuation is 0.2, the 266 laser generated by CLBO cannot meet the stability requirements for semiconductor detection. When the temperature fluctuation is reduced to below 0.02, it can meet the stability requirements for laser detection. In theory, the smaller the fluctuation, the better. 0.2 ＜0.02 Frequency conversion stability Long-term instability Long-term stability High temperature produces gaseous impurities The mechanism of CLBO crystal deliquescing is not clear yet, but some gaseous impurities will accelerate the deliquescing process, and gaseous fluoride has a greater impact on the stability of CLBO crystals. yes no Particles generated during use Particles will adhere to the surface of the crystal. Large diameter particles will cause the crystal to be unusable due to surface damage. yes no Can the thermal expansion strain be fully absorbed? Fully absorb thermal expansion strain and greatly extend the service life of the crystal. When the crystal generates stress, the directivity of the output light deteriorates. no yes Dedicated temperature controller No special meaning, but more practical yes no Temperature control upper limit (℃) No special meaning 180℃ 200℃ Crystal end temperature fluctuation The temperature gradient of the crystal. The larger the temperature gradient of the crystal, the more unstable the internal optical path, the greater the impact on the crystal geometry, and the great impact on the stability of the output light, causing the direction of the output light to change continuously and the power fluctuation of the output light to increase. ＜2℃ ±0.01℃

[0051] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A clean furnace device based on a sealed bimetal cavity to control the temperature of a laser crystal, characterized in that: It comprises a front barrel, a furnace and a rear barrel which are coaxially assembled in sequence; the furnace is a cylindrical metal body with an L-shaped through hole in the axial direction, and the crystal is pressed and fixed in the L-shaped through hole by at least one stopper with a strain compensation spring; the front barrel and the rear barrel are metal cylinders with an axial through hole in the middle, one end of which is a window mirror end for installing a window mirror, and the other end has a first flange connection plate, called the furnace end, which is used to connect with the furnace and is sealed by a furnace sealing ring to form a seal. An inner clean cavity; the middle parts of the front barrel and the rear barrel also have a second flange connection plate; the inner clean cavity is arranged in the outer air cavity, and the outer air cavity is surrounded by a front cover, a rear cover, a top cover and a base, and the front cover, the rear cover, the top cover and the base are all made of metal, and the front cover and the rear cover are respectively connected to the second flange plates of the front barrel and the rear barrel, and an air barrier is provided between the inner clean cavity and the outer air cavity; the window mirror ends of the front barrel and the rear barrel extend out of the front cover or the rear cover and extend out of the outer air cavity; The outer cylindrical surface of the furnace chamber has a countersunk hole, and the heating rod and the temperature probe are inserted into the furnace chamber through the countersunk hole; it also includes a temperature controller for adjusting the heating power of the heating rod and detecting the temperature probe signal. The temperature controller is arranged outside the clean furnace, and the temperature controller is electrically connected to the heating rod and the temperature probe.

2. A clean furnace device based on a sealed bimetal cavity to control the temperature of a laser crystal according to claim 1, characterized in that: The window mirror ends of the front barrel and the rear barrel are sealed by metal sealing gaskets.

3. A clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity according to claim 2, characterized in that: The window mirror is a lens coated with an anti-reflection film. The window mirror and the metal sealing gasket are pressed against the window mirror ends of the front barrel and the rear barrel by using a window mirror fastening nut to form a sealed end face through which the laser can pass.

4. A clean furnace device for controlling the temperature of a laser crystal based on a sealed bimetal cavity according to claim 2 or 3, characterized in that: The metal sealing gasket is indium or indium alloy.

5. The clean furnace device based on sealed bimetal cavity to control the temperature of laser crystal according to claim 1, characterized in that: The furnace sealing ring is made of red copper; the limit block is made of red copper; the strain compensation spring is made of spring steel and has an M-shaped shape.

6. A clean furnace device based on a sealed bimetal cavity to control the temperature of a laser crystal according to claim 1, characterized in that: The furnace is made of metal, and the number of the countersunk holes is 6, which are used to install 1 temperature probe and 5 heating rods.

7. The clean furnace device based on sealed bimetal cavity to control the temperature of laser crystal according to claim 1, characterized in that: The temperature probe has a diameter of 4 mm and a length of 15 mm.

8. The clean furnace device based on sealed bimetal cavity to control the temperature of laser crystal according to claim 1, characterized in that: The heating rod is a stainless steel shell inner outlet type heating rod with a diameter of 4 mm and a length of 15 mm, and a power of 8W to 14W.

9. The clean furnace device for controlling the temperature of laser crystal based on sealed bimetal cavity according to claim 1, characterized in that: The insulation layers of the temperature probe wire and the signal wire or power wire of the heating rod are made of high temperature resistant glass wool.

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