A method for laser welding of quartz glass for atomic cells and an atomic cell

Abstract

This invention discloses a laser welding method for quartz glass and an atomic gas chamber, belonging to the field of atomic gas chamber encapsulation technology. The method involves butt-joining first and second quartz glass components to form a bonding interface, and then welding using a CO2 laser beam, divided into two steps: pre-welding and main welding. During pre-welding, a first laser power scan is used to form multiple discrete weld points to fix the components; during main welding, a higher second laser power is used for continuous scanning to form a sealing weld. The spacing between adjacent weld points formed in the pre-welding is less than 1.5 times the diameter of the main welding spot, ensuring that the main weld completely covers and fuses the discrete points, guaranteeing a continuous and uniform weld. By controlling the laser power and scanning speed, the weld penetration depth is stabilized at 0.5 mm to 2 mm, with an airtightness better than 8×10⁻⁶ mm. ‑11 Pa·m³ / s, with a heat-affected zone width of less than 1.5 mm. This invention also discloses an atomic gas chamber prepared using this method, which can avoid component displacement and stress concentration, achieve high airtightness and low heat-affected zone sealing welding, and improve the long-term stability of the atomic gas chamber.

Description

Technical Field

[0001] This invention relates to the field of atomic gas chamber encapsulation technology, and more specifically, to a laser welding method for a quartz glass atomic gas chamber and the atomic gas chamber itself. Background Technology

[0002] The atomic gas chamber is a core component of quantum precision measurement devices such as atomic clocks and atomic magnetometers. It is typically composed of a light-transmitting window and a sealed cavity base, and is encapsulated with alkali metals (such as cesium and rubidium) or iodine vapor. The quality of its sealing directly determines the coherence time of atoms and the long-term stability of the device.

[0003] Existing methods for sealing atomic gas chambers mainly include anodic bonding and high-temperature fusion bonding. Anodic bonding typically requires high voltage and temperature (300℃-400℃) and is mostly used for silicon-glass structures, with limited adaptability to all-quartz glass devices. High-temperature fusion bonding easily introduces significant thermal stress, leading to birefringence in the window and affecting optical performance. In recent years, laser welding technology has been explored for glass encapsulation due to its advantages such as localized heating, small heat-affected zone, and non-contact processing. However, existing laser welding methods are mostly geared towards general optical component encapsulation and have not been optimized for the specific requirements of atomic gas chambers. Atomic gas chambers require extremely high weld airtightness (typically better than 1.0 × 10⁻⁶). -10 (Pa·m³ / s), and the heat-affected zone and spatter during the welding process must be strictly controlled to avoid contamination of the internal optical window or reaction of the alkali metal / iodine filled later.

[0004] Russian patent RU2554358C1 and its related improved patents RU2676296C1 and RU2677154C1 disclose a method for preparing an atomic gas chamber using CO2 laser welding of a glass window. These patents constitute the basic technical framework for laser-sealed atomic gas chambers in this field, addressing the fundamental technological problem of "how to achieve laser sealing of the atomic gas chamber," focusing on the integrity and feasibility of the welding steps. However, the evaluation of the welding effect remains at the qualitative descriptive level (such as "improved light transmittance" and "saving alkali metals"), without providing specific numerical indicators of airtightness. Specific laser welding parameters (power, scanning speed, spot diameter, etc.) are not disclosed, and the technical solutions rely on operator experience for adjustment. Furthermore, the potential risks of welding heat effects on subsequent alkali metal filling are not fully considered in the assessment of their impact on subsequent processes.

[0005] This invention addresses the challenge of achieving both ultra-high airtightness and a minimal heat-affected zone during laser sealing of quartz glass. To this end, it proposes a two-stage welding process combining pre-welding and main welding: the pre-welding step temporarily fixes the component through discrete weld points, preventing relative displacement caused by thermal expansion during the main welding process; the main welding step forms a continuous, sealed weld. Furthermore, this invention defines the relationship between the pre-welding weld point spacing and the main welding spot diameter (the spacing is less than 1.5 times the main welding spot diameter, preferably 0.8 to 1.2 times), ensuring that the laser completely covers the pre-welding point gaps during the main welding process, while avoiding localized stress concentration caused by heat accumulation, thereby achieving synergistic optimization of weld uniformity and consistency.

[0006] In terms of quantitative indicators, this invention explicitly proposes that the weld airtightness is better than 8×10. -11 The technical standards of Pa·m³ / s, heat-affected zone width less than 1.5 mm, and penetration depth stable between 0.5 mm and 2 mm provide verifiable quantitative evidence for welding quality. Simultaneously, this invention incorporates experimentally verified process parameters such as laser power, scanning speed, and spot diameter into the technical solution, ensuring the repeatability and transferability of the welding process and reducing the uncertainty of technology implementation. Regarding the impact on subsequent processes, by controlling the heat-affected zone width to less than 1.5 mm, this invention actively avoids optical film and window surface shape failures caused by overheating in the window area while ensuring welding efficiency, significantly improving the long-term stability and device consistency of the atomic gas chamber. Summary of the Invention

[0007] The purpose of this invention is to provide a laser welding method for quartz glass in atomic gas chambers, so as to solve the technical problem in the prior art that it is difficult to achieve both ultra-high airtightness and minimal heat-affected zone in the sealing of atomic gas chambers.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A laser welding method for quartz glass in an atomic gas chamber, characterized by comprising the following steps: Step 1: Provide a first quartz glass component and a second quartz glass component, wherein the first quartz glass component and the second quartz glass component constitute at least a portion of the atomic gas chamber; Step 2: Connect the first quartz glass component and the second quartz glass component to form a joint interface; Step 3: Laser welding is performed along the joint interface using a CO2 laser beam. The laser welding includes a pre-welding step and a main welding step. In the pre-welding step, a first laser power is used to scan along the bonding interface to form multiple discrete welding points, temporarily fixing the first quartz glass component and the second quartz glass component. In the main welding step, a second laser power is used to continuously scan along the joint interface to form a continuous airtight sealing weld. Wherein, the second laser power is greater than the first laser power, and the distance between adjacent fusion points in the pre-welding step is less than 1.5 times the diameter of the laser spot in the main welding step; By controlling the laser power and welding scanning speed, the weld penetration depth is stabilized between 0.5 mm and 2 mm, thereby ensuring that the airtightness of the gas chamber is better than 8×10. -11 Pa·m³ / s, and the width of the weld heat-affected zone is less than 1.5 mm.

[0009] As a preferred embodiment, the CO2 laser has a power of 5W to 100W, a scanning speed of 0.01 mm / s to 5 mm / s, and a spot diameter of 0.2 mm to 2 mm.

[0010] As a preferred embodiment, the spacing between adjacent welding points is set to 0.8 to 1.2 times the diameter of the laser spot in the main welding step, so as to ensure that the laser spot coverage area can completely cover the gap between adjacent pre-welding points during the main welding scan, while avoiding local stress concentration caused by heat accumulation at the pre-welding points.

[0011] As a preferred embodiment, the discrete weld points formed in the pre-welding step are completely covered and remelted by the continuous weld in the main welding step, so that there is no interface between the pre-welding step and the main welding step in the final weld.

[0012] As a preferred option, the welding is performed in a dust removal system controlled environment to avoid dust pollution of the device.

[0013] As a preferred option, stress-relief annealing is performed after welding, with an annealing temperature of 600℃ to 900℃ and a holding time of 1 to 8 hours.

[0014] As a preferred embodiment, the first quartz glass component is a cavity base with an opening or a glass plate of any shape, and the second quartz glass component is a transparent window covering the opening or a glass plate of any shape.

[0015] As a preferred embodiment, the surfaces of the first and second quartz glass components to be welded are cleaned before welding, the cleaning process including organic solvent cleaning and / or plasma cleaning.

[0016] The atomic gas chamber prepared by this method has detectable differences from existing gas chambers in terms of weld morphology, microstructure, and heat-affected zone characteristics.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By using a pre-welding step to temporarily fix the components, relative displacement caused by thermal expansion during the main welding process is avoided, thus improving welding alignment accuracy and yield. 2. Define the relationship between the pre-welding weld point spacing and the main welding spot diameter (spacing < 1.5 times the spot diameter, preferably 0.8~1.2 times) to ensure that the laser can completely cover the pre-welding point gap during the main welding, while avoiding stress concentration caused by heat accumulation; 3. The discrete weld joints formed by pre-welding are completely covered and remelted during the main welding process, and there is no interface between the two stages of welding in the final weld, which ensures the uniformity and airtightness of the weld. 4. While achieving a penetration depth of 0.5~2 mm, the airtightness of the gas chamber is superior to that of 8×10. - ¹¹ Pa·m³ / s, heat-affected zone less than 1.5 mm, meeting the stringent requirements of atomic gas chambers for ultra-high vacuum packaging and low thermal stress. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a laser welding device in the prior art.

[0019] Figure 2 This is a schematic diagram of the atomic gas chamber prepared in an embodiment of the present invention; Figure 3 A photomicrograph of the weld seam of the atomic gas chamber; Figure 4 This is a cross-sectional view of the weld seam in the atomic gas chamber.

[0020] The above schematic diagram is only used to illustrate a method for laser welding of quartz glass for atomic gas chambers and should not be used to limit the scope of protection of this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention. Where there is no conflict, the following embodiments and features described herein can be combined with each other.

[0022] Figure 1 The present invention is a schematic diagram of the structure of a laser welding device in an embodiment of the present invention. The laser welding device includes: a software operating system 1, a control system 2, a multi-axis motion platform 3 including X and Y axes and controlling the sample to rotate around the axis, a laser galvanometer 4, an optical fiber 5 with one end connected to the galvanometer system and the other end connected to a CO2 laser 6, a CO2 laser 6, and a dust removal system 7.

[0023] Figure 2The image shows an atomic gas chamber prepared in an embodiment of the present invention. The atomic gas chamber includes optical end faces 8 at both ends, a basic cavity structure 9 welded to the optical end faces 8, and a tail tube 10 storing alkali metal cesium inside. Figure 3 The image shows a micrograph of the weld seam of the atomic gas chamber. The weld seam area includes the welding area 81 of the optical end face 8 and the welding area 91 of the basic cavity structure 9. As can be seen from the figure, the total width of the weld seam of the atomic gas chamber in this embodiment is 2.2 mm. The width of the heat-affected zone on the lateral circumferential surface of the optical end face 8 is approximately equal to the width of the heat-affected zone on the basic cavity structure, which is about 1.1 mm. Since the two optical end faces of the atomic gas chamber are light-transmitting surfaces, the heat-affected zone generated on the lateral circumferential surface of the optical end face during the welding process does not affect the light-transmitting aperture of the cavity. Figure 4 The figure shows a cross-sectional view of the atomic gas chamber weld. As can be seen from the figure, the atomic gas chamber prepared by the atomic gas chamber preparation method of the present invention has a weld penetration depth of about 0.58 mm.

[0024] Example 1 This embodiment provides a method for laser welding of quartz glass for a cesium atom gas chamber, the specific steps of which are as follows: First, prepare a basic structure of a quartz glass cavity with a circular opening (outer diameter 10mm, wall thickness 1mm) and two quartz glass windows, each 10mm in diameter and 1mm thick. Clean both sequentially with acetone, ethanol, and deionized water using ultrasonic cleaning for 15 minutes each, then dry them with nitrogen gas. Subsequently, place the cavity and windows into a plasma cleaner for surface activation treatment (100W power, 3 minutes).

[0025] The processed window piece is placed over the cavity opening, fixed with a special tooling, and placed on a precision-movable three-dimensional platform.

[0026] A CO2 laser (wavelength 10.6 μm) was used, with a laser power of 5W, a scanning speed of 2 mm / s, and a spot diameter of 0.4 mm. With the dust removal system operating, the laser beam scanned circumferentially along the interface between the window and the cavity to complete the welding.

[0027] After welding, the device is placed in an annealing furnace and heated to 600°C at a rate of 2°C / min, held for 2 hours, and then slowly cooled to room temperature at a rate of 1°C / min to eliminate residual thermal stress generated during welding.

[0028] According to the helium mass spectrometer leak detector test, the leak rate of the weld seam of the atomic gas chamber prepared in this embodiment is less than 5×10⁻⁶. - ¹¹ Pa·m³ / s. Under an optical microscope, the weld penetration depth was 0.58 mm, and the width of the heat-affected zone was approximately 1.1 mm.

[0029] Example 2 This embodiment is basically the same as Embodiment 1, except that it adopts a two-step process of pre-welding and main welding.

[0030] After cleaning and docking, a rapid scan is first performed along the joint interface using a lower laser power (5W) and a faster scanning speed (5 mm / s) to form intermittent spot welds or continuous shallow welds, temporarily fixing the components. Then, the main weld sealing is performed according to the parameters of Example 1 (power 10W, speed 2 mm / s).

[0031] Test results show that, compared to the one-step welding method, the two-step welding method reduces the minute displacement of the window by approximately 60%, achieves higher weld position accuracy, and provides better window edge alignment. The airtightness test results are comparable to those of Example 1, with a leakage rate of 5.0 × 10⁻⁶. -11 Pa·m 3 / s, the width of the heat-affected zone is basically consistent. This embodiment verifies the positive effect of the pre-soldering step on improving the yield of precision packaging.

[0032] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. Where there is no conflict, the above embodiments and features described therein can be combined with each other.

Claims

1. A method for laser welding quartz glass in an atomic gas chamber, characterized in that, Includes the following steps: A first quartz glass component and a second quartz glass component are provided, wherein the first quartz glass component and the second quartz glass component constitute at least a portion of the atomic gas chamber; The first quartz glass component and the second quartz glass component are joined together to form a bonding interface. Laser welding is performed along the joint interface using a CO2 laser beam. The laser welding includes a pre-welding step and a main welding step. In the pre-welding step, a first laser power is used to scan along the bonding interface to form multiple discrete welding points, temporarily fixing the first quartz glass component and the second quartz glass component. In the main welding step, a second laser power is used to continuously scan along the joint interface to form a continuous airtight sealing weld. In this process, the second laser power is greater than the first laser power, and the distance between adjacent weld points in the pre-welding step is less than 1.5 times the laser spot diameter in the main welding step. This is to avoid excessive separation or overlap of the heat-affected zones of adjacent pre-welding points, forming a uniform preheating temperature field and reducing the sensitivity of the weld penetration to process fluctuations during the main welding process. Therefore, by controlling the laser power and scanning speed in the pre-welding and main welding steps, the weld penetration can be stably controlled between 0.5 mm and 2 mm, ensuring that the airtightness of the gas chamber is better than 8×10⁻⁶ mm. -11 Pa·m³ / s, and the width of the weld heat-affected zone is less than 1.5 mm.

2. The method according to claim 1, characterized in that, The CO2 laser has a power of 5 W to 100 W, a scanning speed of 0.01 mm / s to 5 mm / s, and a spot diameter of 0.2 mm to 2 mm.

3. The method according to claim 1, characterized in that, The spacing between adjacent weld points is set to 0.8 to 1.2 times the diameter of the laser spot during the main welding step. When the ratio of the spacing to the spot diameter falls within the range of 0.8 to 1.2, the laser spot coverage area during the main welding process can completely cover the gap between adjacent pre-weld points, and the heat-affected zones of adjacent pre-weld points overlap to form a uniform temperature field, resulting in weld penetration fluctuations of less than ±0.1 mm and airtightness stability better than 8×10⁻⁶ mm. -11 Pa·m³ / s.

4. The method according to claim 1, characterized in that, The discrete weld points formed in the pre-welding step are completely covered and remelted by the continuous weld in the main welding step, so that there is no interface between the pre-welding step and the main welding step in the final weld.

5. The method according to claim 1, characterized in that, The welding is performed in a dust removal system controlled environment to avoid dust contamination of the device.

6. The method according to claim 1, characterized in that, After welding, stress-relief annealing is performed at a temperature of 600℃ to 900℃ for 1 to 8 hours.

7. The method according to claim 1, characterized in that, The first quartz glass component is a cavity base with an opening or a glass plate of any shape, and the second quartz glass component is a transparent window covering the opening or a glass plate of any shape.

8. The method according to claim 1, characterized in that, Before welding, the surfaces of the first and second quartz glass components to be welded are cleaned, including organic solvent cleaning and / or plasma cleaning.

9. An atomic gas chamber, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

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