An all-welded Ramsey microwave resonator cavity for a cold atom fountain clock

Abstract

The present application relates to a kind of all-welded Ramsey microwave resonant cavity for cold atom fountain clock, comprising: Ramsey resonant cavity, flight area waveguide, cutoff waveguide and microwave feed system, flight area waveguide is arranged above Ramsey resonant cavity, the upper portion of flight area waveguide constitutes non-enclosed atom free flight passage;Flight area waveguide is connected by welding cutoff waveguide;Cutoff waveguide is integrally connected Ramsey resonant cavity;Microwave feed system is connected by welding Ramsey resonant cavity.The present application realizes the all-cavity integration structure by integral welding process, completely eliminates microwave leakage hidden danger, and no longer needs to repeat debugging after welding, reduces the resonant cavity tuning period, especially suitable for low-temperature working environment scene.At the same time, through non-enclosed atom free flight passage, it is convenient for vacuum system to maintain the high vacuum state in flight area, so that the loss of cold atom cluster is reduced, and atom signal is larger.

Description

Technical Field

[0001] This invention belongs to the field of cold atom microwave clocks, specifically relating to a fully welded Ramsey microwave resonant cavity for cold atom fountain clocks. Background Technology

[0002] The cold atom fountain clock, as a core device of the high-precision time and frequency standard, directly affects the stability and accuracy of International Atomic Time. The Ramsey microwave resonant cavity is a key component for realizing the interaction between atoms and microwaves; its performance defects can cause microwave leakage frequency shift, becoming a major factor restricting the frequency uncertainty and stability of the fountain clock. Existing solutions for suppressing microwave leakage frequency shift mainly fall into two categories: active suppression schemes, such as those using Mach-Zehnder interferometers, employ rapid frequency switching technology to control the timing and frequency of the fed microwaves. However, active suppression schemes generally rely on the stability of the external environment, exhibiting poor environmental adaptability and failing to fundamentally eliminate leakage frequency shift. Passive suppression schemes reduce microwave leakage through fasteners and mechanical sealing structures, and establish a closed top atom ejection zone on the Ramsey cavity's cutoff waveguide to suppress microwave leakage frequency shift in the upper flight region's atom channels; these schemes have gained widespread application.

[0003] The existing Ramsey resonant cavity employs a combination of a cylindrical cavity and a cutoff waveguide, with components connected via fasteners. In a typical design, cutoff waveguides are placed above and below the resonant cavity to suppress microwave leakage through cavity openings caused by cold atom clusters. Components are sealed together using titanium alloy screws pressed against indium wires. While this structure can suppress microwave power leakage under stable external physical conditions, for ultracold cesium atomic fountain clocks, the Ramsey microwave cavity operates at liquid nitrogen temperature (80K), while microwave cavity tuning can only be performed at room temperature. This creates a significant temperature difference (up to 220K) between the tuning and operating environments. Furthermore, because the connection points between components involve three materials (titanium alloy screws, indium wires, and the component material) with different coefficients of thermal expansion, the significant temperature difference between the operating and tuning environments means that even after room temperature tuning, microwave leakage remains a potential hazard at the liquid nitrogen temperature. Furthermore, after the high and low temperature processes, the mechanical stress caused by the difference in thermal deformation of different materials can reduce the tightening effect of titanium alloy fasteners, forming a potential microwave leakage channel and posing a threat to the mechanical structural strength of the cavity. To release mechanical stress, after using titanium alloy screws to tighten and indium wires to seal various components, at least two weeks of debugging time is required. During the stress release process, the resonant frequency of the resonant cavity will decrease, with a deviation of several hundred kHz. During this period, the titanium alloy screws need to be tightened appropriately to compensate for the reduced frequency until the center frequency of the resonant cavity stabilizes at 9.192632 GHz ± 10 kHz. If the screws are tightened too much, the frequency cannot be reduced to a usable range during the stress release process. In this case, the titanium screws and indium wires must be removed, and the microwave cavity must be refilled and retuned, increasing the time cost. In addition, the existing solution, which uses a sealed top atom ejection zone at the top of the free-flight atom region to suppress leakage, will affect the vacuum pump's pumping efficiency, leading to a decrease in the vacuum level of the flight region and exacerbating the loss of atomic clusters.

[0004] Therefore, in order to eliminate the frequency shift caused by microwave leakage within the cavity and suppress the microwave leakage frequency shift in the free-flight region, a Ramsey microwave resonant cavity structure is needed. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an all-welded Ramsey microwave resonant cavity for cold atom fountain clocks. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] This invention provides an all-welded Ramsey microwave resonator for a cold atom fountain clock, comprising: a Ramsey resonator, a flight waveguide, a cutoff waveguide, and a microwave feed system, wherein the flight waveguide is disposed above the Ramsey resonator, and the area above the flight waveguide forms an unclosed free-flight channel for atoms; the flight waveguide is welded to the cutoff waveguide; the cutoff waveguide is welded to the Ramsey resonator; and the microwave feed system is integrally connected to the Ramsey resonator.

[0007] In one embodiment of the present invention, the Ramsey resonant cavity is a cylindrical cavity, and the top and bottom of the cylindrical cavity are provided with atomic channel holes.

[0008] In one embodiment of the present invention, the flight zone waveguide includes: a flight zone upper cutoff waveguide and a flight zone waveguide connected sequentially from top to bottom. The flight zone upper cutoff waveguide and the flight zone waveguide are an integral structure, and the flight zone waveguide is connected to the cutoff waveguide by welding.

[0009] In one embodiment of the present invention, the diameter of the cutoff waveguide in the flight area is smaller than the diameter of the waveguide in the flight area.

[0010] In one embodiment of the present invention, the cutoff waveguide includes: an upper cutoff waveguide and a lower cutoff waveguide, wherein the first end of the upper cutoff waveguide is connected to the flight region waveguide by welding, the second end of the upper cutoff waveguide is connected to the first end of the Ramsey resonant cavity, and forms an integral structure with the Ramsey resonant cavity; the lower cutoff waveguide is connected to the second end of the Ramsey resonant cavity, and forms an integral structure with the Ramsey resonant cavity.

[0011] In one embodiment of the present invention, the microwave feed system includes a rectangular waveguide, a rectangular waveguide cover, and a semi-rigid cable, wherein the rectangular waveguide and the rectangular waveguide cover are connected by welding; and the semi-rigid cable is connected to the rectangular waveguide by welding.

[0012] In one embodiment of the present invention, at least two rectangular waveguides are provided, and the two rectangular waveguides are symmetrically arranged on both sides of the Ramsey resonant cavity; the rectangular waveguides and the Ramsey cavity are integrally machined structures.

[0013] In one embodiment of the present invention, the Ramsey resonant cavity, the upper cutoff waveguide of the flight zone, the waveguide of the flight zone, the upper cutoff waveguide of the resonant cavity, the lower cutoff waveguide of the resonant cavity, the rectangular waveguide, and the waveguide cap are all made of oxygen-free copper material; the outer layer of the semi-rigid cable is made of oxygen-free copper material, the core wire is made of silver-plated oxygen-free copper material, and the dielectric layer is made of polytetrafluoroethylene material.

[0014] In one embodiment of the present invention, the flight zone waveguide and the upper cutoff waveguide of the resonant cavity, the upper cutoff waveguide of the resonant cavity and the Ramsey resonant cavity, the lower cutoff waveguide of the resonant cavity and the Ramsey resonant cavity, and the waveguide cover and the rectangular waveguide are all sealed and connected by electron beam welding; the semi-rigid cable is connected to the rectangular waveguide by lead-free solder welding.

[0015] In one embodiment of the present invention, the all-welded Ramsey microwave resonator for the cold atom fountain clock employs two-stage coupling: the first stage coupling is the semi-rigid cable coupled to the rectangular waveguide, and the second stage coupling is the rectangular waveguide coupled to the Ramsey resonator; wherein the first stage coupling is electrical coupling, and the second stage coupling is pinhole coupling.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] The fully welded Ramsey microwave resonant cavity for cold atom fountain clocks of this invention achieves a one-piece structure throughout the cavity through an integral welding process. This completely eliminates the microwave leakage risks caused by the thermal expansion differences of materials in traditional indium wire seals and titanium alloy fasteners. Furthermore, after welding, no repeated adjustments are required, reducing the resonant cavity tuning cycle, making it particularly suitable for low-temperature operating environments. Simultaneously, the non-enclosed atom free-flight channel facilitates the vacuum system in maintaining a high vacuum state within the flight zone, reducing the loss of cold atom clusters and resulting in a stronger atomic signal.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an all-welded Ramsey microwave resonator for a cold atom fountain clock provided in an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the welding position of the all-welded Ramsey microwave resonator for a cold atom fountain clock provided in an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram of the working state of the all-welded Ramsey microwave resonator for a cold atom fountain clock provided in an embodiment of the present invention.

[0022] Reference numerals: 100-Ramsey resonant cavity; 200-flight area waveguide; 210-flight area upper cutoff waveguide; 220-flight area waveguide; 300-cutoff waveguide; 310-resonant cavity upper cutoff waveguide; 320-resonant cavity lower cutoff waveguide; 400-microwave feed system; 410-rectangular waveguide; 420-rectangular waveguide cover; 430-semi-rigid cable; 10-first welding position; 20-second welding position; 30-third welding position; 40-fourth welding position. Detailed Implementation

[0023] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, describes a fully welded Ramsey microwave resonant cavity for a cold atom fountain clock proposed according to the present invention.

[0024] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0025] Example 1

[0026] The main drawbacks of existing Ramsey resonators lie in their material compatibility and structural reliability. The multi-material interconnected structure generates mechanical stress due to differences in thermal expansion coefficients during high and low temperature cycling. This stress can not only compromise the seal and cause microwave leakage, but also lead to frequency shifts in the resonator, forcing the system into a stress-relief tuning cycle that can last for several weeks. Meanwhile, while the flight zone sealing design suppresses microwave leakage, the difficulty in maintaining a vacuum causes attenuation of atomic signals. These problems make it difficult for existing resonators to simultaneously achieve high precision, environmental adaptability, and engineering practicality. Therefore, structural innovation is urgently needed to suppress microwave leakage at its source and improve system robustness.

[0027] like Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of the structure of an all-welded Ramsey microwave resonator for a cold atom fountain clock provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the welding position of the fully welded Ramsey microwave resonator for a cold atom fountain clock provided in an embodiment of the present invention.

[0028] In this embodiment, the all-welded Ramsey microwave resonator for a cold atom fountain clock includes: a Ramsey resonator 100, a flight waveguide 200, a cutoff waveguide 300, and a microwave feed system 400. The flight waveguide 200 is disposed above the Ramsey resonator 100, and the area above the flight waveguide 200 forms an unclosed free-flying atom channel. The flight waveguide 200 is welded to the cutoff waveguide 300. The cutoff waveguide 300 is welded to the Ramsey resonator 100. The microwave feed system 400 is integrally connected to the Ramsey resonator 100.

[0029] In one alternative implementation, the Ramsey resonant cavity 100 is a cylindrical cavity, and the top and bottom of the cylindrical cavity are provided with atomic channel apertures.

[0030] In an optional embodiment, the flight area waveguide 200 includes a flight area upper cutoff waveguide 210 and a flight area waveguide 220 connected sequentially from top to bottom. The flight area upper cutoff waveguide 210 and the flight area waveguide 220 are an integral structure, and the flight area waveguide 220 is connected to the cutoff waveguide 300 by welding.

[0031] For example, the diameter of the cutoff waveguide 210 in the flight area is smaller than the diameter of the waveguide 220 in the flight area.

[0032] Preferably, the inner diameter of the flight zone waveguide 220 is 20mm, and the inner diameter of the upper cutoff waveguide 210 in the flight zone is 12mm. Since the inner diameter of the flight zone waveguide 220 is 8mm larger than that of the upper cutoff waveguide 210 in the flight zone, the requirements for coaxiality in machining are reduced.

[0033] It is worth noting that the upper part of the flight zone waveguide 200 forms a non-enclosed free-flight channel for atoms, that is, an opening is provided above the upper cutoff waveguide 210 in the flight zone. Functionally and structurally, the flight zone waveguide 200 can be divided into the upper cutoff waveguide 210 and the flight zone waveguide 220. The flight zone waveguide 220 is the free-flight zone for cold atom clusters. The non-enclosed design reduces the requirements for coaxiality in the machining of the hollow area of ​​the flight zone waveguide 220, making it less likely for cold atom clusters to adhere to the inner wall and cause cold atom loss. The upper cutoff waveguide 210 is used to suppress the microwave power frequency shift caused by ionized microwaves from the external environment (such as microwaves leaked from frequency synthesis systems, cables, and high-frequency adapters) when cold atom clusters are freely flying in the flight zone. Compared with a closed structure, the non-enclosed structure makes it easier for the vacuum system to maintain a high vacuum state in the flight zone, thus reducing the loss of cold atom clusters and resulting in a larger atomic signal.

[0034] In one optional embodiment, the cutoff waveguide 300 includes an upper cutoff waveguide 310 and a lower cutoff waveguide 320, wherein the first end of the upper cutoff waveguide 310 is connected to the flight region waveguide 220 by welding, the second end of the upper cutoff waveguide 310 is connected to the first end of the Ramsey resonant cavity 100, and forms an integral structure with the Ramsey resonant cavity 100; the lower cutoff waveguide 320 is connected to the second end of the Ramsey resonant cavity 100, and forms an integral structure with the Ramsey resonant cavity 100.

[0035] For example, the upper cutoff waveguide 310 and the lower cutoff waveguide 320 of the resonant cavity are located at the two ends of the Ramsey resonant cavity 100, respectively.

[0036] For example, the inner diameter of the upper cutoff waveguide 310 and the lower cutoff waveguide 320 of the resonant cavity is 12 mm, the outer diameter is 18 mm, and the length is 70 mm. They are used to attenuate microwaves with a frequency of hyperfine transition of cesium atoms, and the attenuation degree is greater than 130 dB.

[0037] In an optional embodiment, the microwave feed system 400 includes a rectangular waveguide 410, a rectangular waveguide cover 420, and a semi-rigid cable 430, wherein the rectangular waveguide 410 and the rectangular waveguide cover 420 are connected by welding; and the semi-rigid cable 420 is connected to the rectangular waveguide 410 by welding.

[0038] For example, at least two rectangular waveguides 410 are provided, and the two rectangular waveguides 410 are symmetrically arranged on both sides of the Ramsey resonant cavity 100. Each rectangular waveguide 410 is provided with a rectangular waveguide cover 420.

[0039] In this embodiment, the Ramsey resonant cavity 100, the upper cutoff waveguide 210 of the flight zone, the waveguide 220 of the flight zone, the upper cutoff waveguide 310 of the resonant cavity, the lower cutoff waveguide 320 of the resonant cavity, the rectangular waveguide 410, and the rectangular waveguide cover 420 are all made of oxygen-free copper material; the outer layer of the semi-rigid cable 430 is made of oxygen-free copper material, the core wire is made of silver-plated oxygen-free copper material, and the dielectric layer is made of polytetrafluoroethylene material.

[0040] In this embodiment, the flight zone waveguide 220 and the upper cutoff waveguide 310 of the resonant cavity, the upper cutoff waveguide 310 and the Ramsey resonant cavity 100, the lower cutoff waveguide 320 and the Ramsey resonant cavity 100, and the rectangular waveguide cover 420 and the rectangular waveguide 410 are all sealed and connected by electron beam welding. The semi-rigid cable 430 is connected to the rectangular waveguide 410 by lead-free solder. After welding at each location, vacuum leak testing is required to ensure the smoothness and flatness of the weld. Figure 2As shown, the welding point between the flight zone waveguide 220 and the upper cutoff waveguide 310 of the resonant cavity is the first welding position 10, the welding point between the rectangular waveguide cover 430 and the rectangular waveguide 410 is the second welding position 20, the welding point between the upper cutoff waveguide 310 of the resonant cavity and the Ramsey resonant cavity 100 is the third welding position 30, and the welding point between the lower cutoff waveguide 320 of the resonant cavity and the Ramsey resonant cavity 100 is the fourth welding position 40.

[0041] Specifically, after electron beam welding is completed, the mechanical structure is removed, and then the semi-rigid cable 430 and the rectangular waveguide 410 are welded with lead-free solder in a nitrogen protective gas or vacuum environment to achieve an integrated welding microwave cavity. This cavity is not affected by external free excitation microwaves and has no microwave leakage.

[0042] It is worth noting that in this embodiment, all machined components in the fully welded Ramsey microwave resonant cavity for the cold atom fountain clock are made of oxygen-free copper, and electron beam welding is used to seal the machined components. Before welding, the mechanical structural components of the cavity are mechanically pressed together to ensure a tight fit between the parts. This welding method does not introduce other solder, ensuring the consistency of the cavity material after welding. The semi-rigid cable 430 is connected to the rectangular waveguide 410 by lead-free solder. Since a purely mechanical connection method is no longer used, the potential microwave leakage caused by the different thermal expansion coefficients of different materials is eliminated, as is the microwave leakage frequency shift that may exist at the connection point, enhancing temperature adaptability and mechanical robustness. This structure can not only meet the requirements of ultra-low temperature cesium atomic fountain clocks that are tuned at room temperature and operate at low temperatures (such as liquid nitrogen temperature), but also meet the requirements of room temperature fountain clocks.

[0043] Furthermore, the integrated welding eliminates the microwave leakage risks caused by differences in thermal expansion of materials in traditional indium wire seals and titanium alloy fasteners, while also enhancing temperature adaptability and mechanical robustness. The elimination of screw connections between machined parts also helps reduce the overall size and lowers the difficulty of vacuum maintenance. Compared to existing structures, the overall volume, excluding the flight zone, can be reduced by one-third, allowing for a smaller vacuum maintenance area and reducing the difficulty of vacuum maintenance, thus facilitating the miniaturization of the fountain clock. Moreover, the elimination of screw fastenings and indium wire seals eliminates frequency shifts caused by mechanical aging. After cavity tuning and welding are completed, there is no need for waiting or tuning adjustments, reducing the resonant cavity tuning cycle. Furthermore, after passing vacuum leak testing, zero microwave leakage at the connection points can be achieved.

[0044] The working principle of the all-welded Ramsey microwave resonator of the cold atom fountain clock in this embodiment is as follows: The all-welded Ramsey microwave resonator used in the cold atom fountain clock adopts two-stage coupling. The first stage coupling is a semi-rigid cable 430 coupled to a rectangular waveguide 410, and the second stage coupling is a rectangular waveguide 410 coupled to the Ramsey resonator 100. Among them, the first stage coupling is electrical coupling, and the second stage coupling is pinhole coupling.

[0045] Specifically, the upper cutoff waveguide 210 in the flight zone is used to suppress the microwave power frequency shift caused by ambient microwaves during the free flight of cold atom clusters. The upper cutoff waveguide 310 in the resonant cavity is used to suppress the microwave power frequency shift caused by the small aperture above the Ramsey resonant cavity 100 during the free flight of cold atom clusters. The lower cutoff waveguide 320 in the resonant cavity is used to suppress microwave power leakage from the small aperture below the Ramsey resonant cavity 100. The semi-rigid cable 430 is soldered to the rectangular waveguide 410 using lead-free solder and is used to feed the excitation microwaves of the frequency synthesis system into the rectangular waveguide 410.

[0046] For example, the rectangular waveguide 410 is in TE11 mode; the Ramsey resonator 100 is in TE011 mode. The two-stage coupling method is used to reduce the interference to the field distribution inside the cavity during the coupling process, and the dual-end feeding scheme is used to reduce the frequency shift of the cavity phase distribution.

[0047] The Ramsey cavity has a small opening to allow cold atomic clusters to pass through the cavity twice—up and down—to achieve the Ramsey transition. However, the presence of this opening disrupts the closed circular waveguide structure at both ends of the cylindrical cavity, causing microwaves to leak out. Therefore, the opening in the Ramsey resonant cavity needs to be designed. By incorporating a cutoff waveguide at the opening, the opening can both satisfy the need for cold atomic clusters to pass through the cavity and suppress microwave leakage.

[0048] Circular waveguides can exist in various modes, with the fundamental mode being the TE11 mode, whose frequency is the cutoff frequency. When the excitation microwave frequency is lower than the cutoff frequency, the excitation microwave is an evanescent wave, and its field components attenuate rapidly in an exponential manner within the waveguide, thus achieving the function of cutting off the propagation of the excitation microwave. The cutoff frequency and attenuation rate are related to the aperture diameter, and the total attenuation is the result of the combined effect of the aperture diameter and the waveguide length. The circular waveguide is designed at the aperture location to rapidly attenuate the microwaves within the cavity and suppress microwave leakage; therefore, this circular waveguide is called a cutoff waveguide.

[0049] For example, in a Cs atomic fountain clock, the excitation microwave frequency is 9.192631770 GHz, and the maximum inner diameter of the cutoff waveguide in a vacuum environment is 19.1 mm. With a 5% margin in the design, the minimum cutoff frequency of the cutoff waveguide is designed to be greater than 9.68 GHz, corresponding to an inner diameter of 18.2 mm and an attenuation rate of 536 dB / m. If the inner diameter is 12 mm, the attenuation rate is 2074 dB / m. The smaller the inner diameter, the greater the attenuation rate of the cutoff waveguide, and the shorter the cutoff waveguide length required to achieve the same cutoff effect. For a Cs atomic fountain clock, while ensuring the passage of cold atomic clusters through the cavity, the inner diameter of the cutoff waveguide 300 can be set to 10 mm to 14 mm, with a total length greater than 60 mm. This length and size of the cutoff waveguide 300 are also suitable for the cutoff waveguide 210 in the flight zone, used to suppress the influence of external ionized microwaves.

[0050] For example, in an Rb atomic fountain clock, the excitation microwave frequency is 6.8346826 GHz, and the corresponding maximum radius of the cutoff waveguide in a vacuum environment is 25.7 mm. With a 5% margin in the design, the minimum cutoff frequency of the cutoff waveguide is designed to be greater than 7.18 GHz, corresponding to an inner diameter of 24.5 mm and an attenuation rate of 394 dB / m. If the inner diameter is 12 mm, the attenuation rate is 2356 dB / m. The smaller the inner diameter, the greater the attenuation rate of the cutoff waveguide, and the shorter the cutoff waveguide length required to achieve the same cutoff effect. For an Rb atomic fountain clock, while ensuring the passage of cold atomic clusters through the cavity, the inner diameter of the cutoff waveguide 300 can be set to 12 mm to 18 mm, and the length greater than 60 mm. This length and size of the cutoff waveguide 300 are also suitable for the cutoff waveguide 210 in the flight zone, used to suppress the influence of external ionized microwaves.

[0051] like Figure 3 As shown, Figure 3 This is a schematic diagram of the working state of the all-welded Ramsey microwave resonator for a cold atom fountain clock provided in an embodiment of the present invention.

[0052] Taking cesium atoms (Cs) as an example, the operation of the cold atom fountain clock incorporating the all-welded Ramsey microwave resonant cavity of the present invention is as follows:

[0053] S1. Cs atomic vapor in the vacuum chamber is cooled by laser to form cold atomic clusters, with Cs atoms evenly distributed in each |F=4>m F At the sub-level, cold atom clusters are then thrown upwards using a moving optical clustering technique. After leaving the cold atom preparation region, the cold atom clusters sequentially pass through the state-selection cavity, the fluorescence collection and detection region, the Ramsey cavity, and the free-flight region, before falling back into the Ramsey cavity, completing the entire Ramsey process.

[0054] S2. Under the action of the first microwave power π pulse in the selected cavity below the lower cutoff waveguide 320 of the resonant cavity, at |F=4,mF =0> Atoms pumped to |F=3,m on the energy level. F =0> energy level, and |F=4,m F Atoms with ≠0> do not undergo energy level transitions;

[0055] S3.Cs atoms continue to rise, and the fluorescence collection and detection region between the selected cavity and the resonant cavity cutoff waveguide 320 is removed by the repulsive light |F=4,m F For atoms in energy levels ≠ 0, only |F = 3,m is retained. F =0> Atom;

[0056] S4. Subsequently, |F=3,m F Cs atoms with a value of 0> enter the Ramsey cavity with a second microwave field having a second microwave power. Under the action of the first π / 2 pulse, the atoms are in a state of |F=3,m F =0> and |F=4,m F =0> superposition state;

[0057] The S5.Cs atom leaves the Ramsey resonant cavity 100 and flies freely, gradually decelerating to zero, reaching a maximum height within the waveguide 200 of the flight region. Subsequently, under the influence of gravity, it begins to fall back, passing through the Ramsey resonant cavity 100 for the second time. Under the action of a second π / 2 pulse of a second microwave field with a second microwave power, the atom completes the entire Ramsey interaction process, and the atomic population reverses to |F=4,m F =0> energy level;

[0058] S6. Cold atom clusters fall back to the detection region located between the Ramsey resonant cavity 100 and the selected cavity. Under the action of probe light 1, repulsive light, and probe light 2, fluorescence collectors 1 and 2 detect |F = 4,m F =0> and |F=3,m F =0> The fluorescence produced by the atoms in the energy level, where fluorescence collection 1 and fluorescence collection 2 are two sets of fluorescence collection devices used to detect the population of the hyperfine energy level of Cs atoms within the fluorescence collection detection region; thus, |F=4,m F =0> and |F=3,m F =0>Cs atom population at energy level, thus completing the entire quantum part of the Cs fountain clock operation.

[0059] The fully welded Ramsey microwave resonant cavity for cold atom fountain clocks of this invention achieves a one-piece structure throughout the cavity through an integral welding process. This completely eliminates the microwave leakage risks caused by the thermal expansion differences of materials in traditional indium wire seals and titanium alloy fasteners. Furthermore, after welding, no repeated adjustments are required, reducing the resonant cavity tuning cycle, making it particularly suitable for low-temperature operating environments. Simultaneously, the non-enclosed atom free-flight channel facilitates the vacuum system in maintaining a high vacuum state within the flight zone, reducing the loss of cold atom clusters and resulting in a stronger atomic signal.

[0060] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0061] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A fully welded Ramsey microwave resonant cavity for a cold atom fountain clock, characterized in that, include: The system comprises a Ramsey resonant cavity (100), a flight zone waveguide (200), a cutoff waveguide (300), and a microwave feed system (400), wherein... The flight zone waveguide (200) is disposed above the Ramsey resonant cavity (100), and the area above the flight zone waveguide (200) forms an unclosed atomic free flight channel; the flight zone waveguide (200) is connected to the cutoff waveguide (300) by welding; the cutoff waveguide (300) is connected to the Ramsey resonant cavity (100) by welding; the microwave feed system (400) is integrally connected to the Ramsey resonant cavity (100); The flight zone waveguide (200) includes an upper cutoff waveguide (210) and a flight zone waveguide (220). The cutoff waveguide (300) includes an upper cutoff waveguide (310) and a lower cutoff waveguide (320) of the resonant cavity. The microwave feed system (400) includes a rectangular waveguide (410), a rectangular waveguide cover (420), and a semi-rigid cable (430). The Ramsey resonant cavity (100), the upper cutoff waveguide (210), the flight zone waveguide (220), the upper cutoff waveguide (310), the lower cutoff waveguide (320), the rectangular waveguide (410), and the rectangular waveguide cover (420) are all made of oxygen-free copper. The outer layer of the semi-rigid cable (430) is made of oxygen-free copper, the core wire is made of silver-plated oxygen-free copper, and the dielectric layer is made of polytetrafluoroethylene. The flight zone waveguide (220) and the upper cutoff waveguide (310) of the resonant cavity, the upper cutoff waveguide (310) of the resonant cavity and the Ramsey resonant cavity (100), the lower cutoff waveguide (320) of the resonant cavity and the Ramsey resonant cavity (100), and the rectangular waveguide cover (420) and the rectangular waveguide (410) are all sealed and connected by electron beam welding; the semi-rigid cable (430) is welded to the side wall of the rectangular waveguide (410) by lead-free solder; and the rectangular waveguide (410) and the Ramsey resonant cavity (100) are integrally machined structures.

2. The all-welded Ramsey microwave resonant cavity for a cold atom fountain clock according to claim 1, characterized in that, The Ramsey resonant cavity (100) is a cylindrical cavity, and the top and bottom of the cylindrical cavity are provided with atomic channel holes.

3. The all-welded Ramsey microwave resonant cavity for a cold atom fountain clock according to claim 1, characterized in that, The flight area waveguide (200) includes a flight area upper cutoff waveguide (210) and a flight area waveguide (220) connected sequentially from top to bottom. The flight area upper cutoff waveguide (210) and the flight area waveguide (220) are an integral structure. The flight area waveguide (220) is connected to the cutoff waveguide (300) by welding.

4. The all-welded Ramsey microwave resonant cavity for a cold atom fountain clock according to claim 3, characterized in that, The diameter of the upper cutoff waveguide (210) in the flight area is smaller than the diameter of the waveguide (220) in the flight area.

5. The all-welded Ramsey microwave resonant cavity for a cold atom fountain clock according to claim 3, characterized in that, The first end of the upper cutoff waveguide (310) of the resonant cavity is connected to the flight zone waveguide (220) by welding. The second end of the upper cutoff waveguide (310) of the resonant cavity is connected to the first end of the Ramsey resonant cavity (100) and forms an integral structure with the Ramsey resonant cavity (100). The lower cutoff waveguide (320) of the resonant cavity is connected to the second end of the Ramsey resonant cavity (100) and forms an integral structure with the Ramsey resonant cavity (100).

6. The all-welded Ramsey microwave resonant cavity for a cold atom fountain clock according to claim 1, characterized in that, At least two rectangular waveguides (410) are provided, and the two rectangular waveguides (410) are symmetrically arranged on both sides of the Ramsey resonant cavity (100).

7. The all-welded Ramsey microwave resonant cavity for a cold atom fountain clock according to claim 1, characterized in that, The all-welded Ramsey microwave resonator used for the cold atom fountain clock employs two-stage coupling: the first stage coupling is the coupling of the semi-rigid cable (430) to the rectangular waveguide (410), and the second stage coupling is the coupling of the rectangular waveguide (410) to the Ramsey resonator (100); wherein, the first stage coupling is electrical coupling, and the second stage coupling is pinhole coupling.

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