All-welded Ramsey microwave resonant cavity for cold atom fountain clock

Abstract

The invention relates to an all-welded Ramsey microwave resonant cavity for a cold atom fountain clock, the all-welded Ramsey microwave resonant cavity comprises a Ramsey resonant cavity, a flying area waveguide, a cut-off waveguide and a microwave feed-in system, the flying area waveguide is arranged above the Ramsey resonant cavity, and a non-closed atom free flight channel is formed above the flying area waveguide; the flying area waveguide is connected with the cut-off waveguide through welding; the cut-off waveguide is integrally connected with the Ramsey resonant cavity; the microwave feed-in system is connected with the Ramsey resonant cavity through welding. According to the invention, a full-cavity integrated structure is realized through an integrated welding process, the hidden danger of microwave leakage is thoroughly eliminated, repeated debugging is not needed after welding is completed, the tuning period of the resonant cavity is shortened, and the resonant cavity is especially suitable for a low-temperature working environment scene. Meanwhile, through a non-closed atom free flight channel, a vacuum system can conveniently keep a high vacuum state in a flight area, so that the loss of cold atom cohesion is reduced, and an atom signal is relatively large.

Description

Technical Field

[0001] The present invention belongs to the field of cold atom microwave clocks, and particularly relates to a fully welded Ramsey microwave resonator for a cold atom fountain clock. Background Art

[0002] As the core device of a high-precision time and frequency standard, the performance of a cold atom fountain clock directly affects the stability and accuracy of international atomic time. The Ramsey microwave resonator is a key component for realizing the interaction between atoms and microwaves. Performance defects thereof may cause microwave leakage frequency shift, which becomes the main factor restricting the frequency uncertainty and stability of the fountain clock. In existing solutions, the suppression of microwave leakage frequency shift is mainly divided into two categories. Active suppression schemes, such as using a Mach-Zehnder interference switch and adopting fast frequency hopping technology to control the timing and frequency of the fed microwave, generally rely on the stability of the external environment and have the problem of poor environmental adaptability, making it difficult to fundamentally eliminate the leakage frequency shift. Passive suppression schemes reduce microwave leakage through fasteners and mechanical sealing structures, and set a closed top atom throwing area on the cut-off waveguide of the Ramsey cavity to suppress the microwave leakage frequency shift of the atomic channel in the upper flight area, and have been widely applied.

[0003] The existing Ramsey resonator adopts a combined structure of a cylindrical cavity and a cutoff waveguide, and the components are connected through fasteners. In a typical solution, the cutoff waveguides designed above and below the resonator cavity are used to suppress the microwave leakage of the cavity holes for cold atom clusters. Between each component, indium wires are sealed by pressing with titanium alloy screws. Although such a structure can achieve the effect of suppressing the microwave power overflow in the cavity under a stable external physical environment. However, for an ultra-cold cesium atomic fountain clock, the Ramsey microwave cavity operates at the liquid nitrogen temperature (80K), while the debugging of the microwave cavity can only be carried out at room temperature. There is a huge temperature difference (up to 220K) between the debugging environment and the working environment of the microwave cavity. At the same time, since there are three materials (titanium alloy screws, indium wires, component materials) at the connection positions between the components, and the thermal expansion coefficients of the three materials are different, when there is a significant temperature difference between the working environment and the debugging environment, there is still a hidden danger of microwave leakage at the component connection after being debugged at room temperature under the liquid nitrogen temperature. In addition, after the high and low temperature process, the mechanical stress caused by the thermal deformation difference of different materials will lead to a decrease in the fastening effect of the titanium alloy fastening screws, forming a potential microwave leakage channel and posing a hidden danger to the mechanical structure strength of the cavity. To release the mechanical stress, after fastening each component with titanium alloy screws and sealing with indium wires, at least more than 2 weeks of debugging time is required. During the stress release process, the resonance frequency of the resonator will decrease, and the offset can reach several hundred kHz. During this period, the titanium alloy screws need to be properly tightened to compensate for the reduced frequency until the center frequency of the resonator is stabilized at 9.192632 GHz ± 10 kHz. If the tightening degree of the screws is too high and the frequency cannot be reduced to the available range during the stress release process, then only the titanium screws and indium wires can be removed, and the microwave cavity needs to be refilled and tuned, increasing the time cost. In addition, in the existing solution, the method of suppressing leakage by setting a sealed top atomic throwing area at the top of the atomic free flight area will affect the pumping efficiency of the vacuum pump, resulting in a decrease in the vacuum degree of the flight area and exacerbating the loss of atomic clusters.

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

[0005] In order to solve the above problems existing in the prior art, the present invention provides a fully welded Ramsey microwave resonator for a cold atom fountain clock. The technical problems to be solved by the present invention are realized through the following technical solutions:

[0006] The present invention provides a fully welded Ramsey microwave resonator for a cold atom fountain clock, comprising: a Ramsey resonator, a flight region waveguide, a cutoff waveguide, and a microwave feeding system. Among them, the flight region waveguide is arranged above the Ramsey resonator, and a non-closed atomic free flight channel is formed above the flight region waveguide; the flight region waveguide is connected to the cutoff waveguide by welding; the cutoff waveguide is connected to the Ramsey resonator by welding; and the microwave feeding system is integrally connected to the Ramsey resonator.

[0007] In an embodiment of the present invention, the Ramsey resonator is a cylindrical cavity, and atomic channel small holes are provided at both the top and the bottom of the cylindrical cavity.

[0008] In an embodiment of the present invention, the flight region waveguide comprises: a flight region upper cutoff waveguide and a flight region waveguide tube connected in sequence from top to bottom. The flight region upper cutoff waveguide and the flight region waveguide tube are an integral structure, and the flight region waveguide tube is connected to the cutoff waveguide by welding.

[0009] In an embodiment of the present invention, the diameter of the flight region upper cutoff waveguide is smaller than the diameter of the flight region waveguide tube.

[0010] In an embodiment of the present invention, the cutoff waveguide comprises: a resonator upper cutoff waveguide and a resonator lower cutoff waveguide. Among them, the first end of the resonator upper cutoff waveguide is connected to the flight region waveguide tube by welding, the second end of the resonator upper cutoff waveguide is connected to the first end of the Ramsey resonator and forms an integral structure with the Ramsey resonator; the resonator lower cutoff waveguide is connected to the second end of the Ramsey resonator and forms an integral structure with the Ramsey resonator.

[0011] In an embodiment of the present invention, the microwave feeding system comprises a rectangular waveguide, a rectangular waveguide cover, and a semi-rigid cable. Among them, the rectangular waveguide is connected to the rectangular waveguide cover by welding; the semi-rigid cable is connected to the rectangular waveguide by welding.

[0012] In an embodiment of the present invention, at least two rectangular waveguides are provided. The two rectangular waveguides are symmetrically arranged on both sides of the Ramsey resonator; the rectangular waveguide and the Ramsey cavity are an integral machining structure.

[0013] In one embodiment of the present invention, the Ramsey resonator, the upper cutoff waveguide in the flight region, the waveguide in the flight region, the upper cutoff waveguide of the resonator, the lower cutoff waveguide of the resonator, the rectangular waveguide, and the waveguide cover 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, between the waveguide in the flight region and the upper cutoff waveguide of the resonator, between the upper cutoff waveguide of the resonator and the Ramsey resonator, between the lower cutoff waveguide of the resonator and the Ramsey resonator, and between the waveguide cover and the rectangular waveguide, they are all hermetically connected by electron beam welding; the semi-rigid cable is welded to the rectangular waveguide by lead-free solder.

[0015] In one embodiment of the present invention, the fully welded Ramsey microwave resonator for a cold atom fountain clock adopts two-stage coupling. The first-stage coupling is that the semi-rigid cable is coupled to the rectangular waveguide, and the second-stage coupling is that the rectangular waveguide is coupled to the Ramsey resonator; wherein, the first-stage coupling is electrical coupling, and the second-stage coupling is aperture coupling.

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

[0017] The fully welded Ramsey microwave resonator for a cold atom fountain clock of the present invention realizes an integrated structure of the entire cavity through an integral welding process, completely eliminating the potential microwave leakage hazard caused by the material thermal expansion difference of traditional indium wire seals and titanium alloy fasteners. After welding, there is no need for repeated debugging, reducing the tuning period of the resonator, and is especially suitable for low-temperature working environment scenarios. At the same time, through the non-enclosed atomic free flight channel, it is convenient for the vacuum system to maintain a high vacuum state in the flight region, reducing the loss of cold atom clusters and resulting in a larger atomic signal.

[0018] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given and described in detail in conjunction with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of a fully welded Ramsey microwave resonator for a cold atom fountain clock provided by an embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of the welding positions of the fully welded Ramsey microwave resonator for a cold atom fountain clock provided by an embodiment of the present invention;

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

[0022] Reference numerals: 100 - Ramsey resonator; 200 - flight region waveguide; 210 - upper cut-off waveguide in the flight region; 220 - flight region waveguide tube; 300 - cut-off waveguide; 310 - upper cut-off waveguide of the resonator; 320 - lower cut-off waveguide of the resonator; 400 - microwave feeding 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. Specific embodiments

[0023] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following combines the accompanying drawings and specific embodiments to detail a fully welded Ramsey microwave resonator 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 can be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of specific embodiments, a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the accompanying drawings are only for reference and illustration, and are not used to limit the technical solution of the present invention.

[0025] Embodiment 1

[0026] The main defects of existing Ramsey resonators mainly focus on material compatibility and structural reliability. In the multi-material connection structure, mechanical stress is generated due to the difference in thermal expansion coefficients during high and low temperature cycles. This not only may damage the sealing and cause microwave leakage, but also leads to frequency offset of the resonator, forcing the system to enter a stress relaxation tuning cycle lasting for several weeks. At the same time, although the sealing design in the flight region suppresses microwave leakage, it causes attenuation of atomic signals due to the difficulty in maintaining vacuum. These problems make it difficult for existing resonators to balance high precision, environmental adaptability, and engineering practicability, and there is an urgent need to achieve source suppression of microwave leakage and improvement of system robustness through structural innovation.

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

[0028] In this embodiment, a fully welded Ramsey microwave resonator for a cold atom fountain clock includes: a Ramsey resonator 100, a flight region waveguide 200, a cutoff waveguide 300, and a microwave feeding system 400. Among them, the flight region waveguide 200 is disposed above the Ramsey resonator 100, and the upper part of the flight region waveguide 200 forms an unenclosed atomic free flight channel; the flight region waveguide 200 is connected to the cutoff waveguide 300 by welding; the cutoff waveguide 300 is connected to the Ramsey resonator 100 by welding; the microwave feeding system 400 is integrally connected to the Ramsey resonator 100.

[0029] In an optional embodiment, the Ramsey resonator 100 is a cylindrical cavity, and atomic channel small holes are provided at both the top and the bottom of the cylindrical cavity.

[0030] In an optional embodiment, the flight region waveguide 200 includes: a flight region upper cutoff waveguide 210 and a flight region waveguide tube 220 that are connected in sequence from top to bottom. The flight region upper cutoff waveguide 210 and the flight region waveguide tube 220 are of an integral structure, and the flight region waveguide tube 220 is connected to the cutoff waveguide 300 by welding.

[0031] Exemplarily, the diameter of the flight region upper cutoff waveguide 210 is smaller than the diameter of the flight region waveguide tube 220.

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

[0033] It should be noted that the upper part of the flight region waveguide 200 forms an unenclosed atomic free flight channel, that is, an opening is provided above the flight region upper cutoff waveguide 210. The flight region waveguide 200 can be functionally and structurally divided into a flight region upper cutoff waveguide 210 and a flight region waveguide tube 220. Among them, the flight region waveguide tube 220 is a free flight region for cold atom clusters. Through the unenclosed design, the requirement for coaxiality in machining of the hollow region of the flight region waveguide tube 220 is reduced, so that the cold atom clusters are not easily adhered to the inner wall, resulting in cold atom loss. The flight region upper cutoff waveguide 210 is used to suppress the microwave power frequency shift of the cold atom clusters during free flight in the flight region caused by external environmental stray microwaves (such as microwaves leaked from a frequency synthesizer system, cables, and high-frequency adapters). Compared with the enclosed structure, the unenclosed structure facilitates the vacuum system to maintain a high vacuum state in the flight region, reducing the loss of cold atom clusters and increasing the atomic signal.

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

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

[0036] Exemplarily, the inner diameters of both the upper cavity cutoff waveguide 310 and the lower cavity cutoff waveguide 320 are 12 mm, the outer diameters are 18 mm, and the lengths are 70 mm, which are used to attenuate microwaves with the frequency of cesium atom hyperfine transition, and the attenuation degree is greater than 130 dB.

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

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

[0039] In this embodiment, the Ramsey cavity 100, the upper flight zone cutoff waveguide 210, the flight zone waveguide 220, the upper cavity cutoff waveguide 310, the lower cavity cutoff waveguide 320, 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, between the flight zone waveguide 220 and the upper cavity cutoff waveguide 310, between the upper cavity cutoff waveguide 310 and the Ramsey cavity 100, between the lower cavity cutoff waveguide 320 and the Ramsey cavity 100, and between the rectangular waveguide cover 420 and the rectangular waveguide 410 are all hermetically connected by electron beam welding. The semi-rigid cable 430 is connected to the rectangular waveguide 410 by lead-free soldering, and vacuum leak detection is required after welding at each welding position, and the weld seams should be smooth and flat. That is, Figure 2As shown, the welding point between the flight area waveguide 220 and the upper cut-off 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 cut-off 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 cut-off waveguide 320 of the resonant cavity and the Ramsey resonant cavity 100 is the fourth welding position 40.

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

[0042] It should be noted that all the machined parts in the fully welded Ramsey microwave resonant cavity for the cold atom fountain clock in this embodiment are made of oxygen-free copper material, and electron beam welding is used for sealing between the machined parts. Before welding, the mechanical structure parts of the cavity are mechanically pressed to ensure close fitting between the parts. This welding method does not introduce other solders and ensures the material consistency of the welded cavity. The semi-rigid cable 430 is welded to the rectangular waveguide 410 with lead-free solder. Since the simple mechanical connection method is no longer used, the hidden danger of microwave leakage caused by different thermal expansion coefficients of different materials is eliminated, and the microwave leakage frequency shift that may exist at the connection is also eliminated, enhancing the temperature environment adaptability and mechanical robustness. This structure can not only meet the requirements of normal temperature tuning and the ultra-low temperature cesium atom fountain clock operating at low temperature (such as liquid nitrogen temperature), but also meet the requirements of the normal temperature fountain clock.

[0043] In addition, due to the integrated welding, not only the hidden danger of microwave leakage caused by the thermal expansion difference of traditional indium wire sealing and titanium alloy fasteners is eliminated, but also the temperature environment adaptability and mechanical robustness are enhanced. Also, since screw connections are no longer required between the machined parts, it is beneficial to reduce the overall size and the difficulty of maintaining vacuum. Compared with the existing structure, the overall volume excluding the flight area can be reduced by 1 / 3, so a smaller vacuum maintenance area can be used, reducing the difficulty of maintaining vacuum and facilitating the miniaturization of the fountain clock. Moreover, since screw fastening and indium wire sealing are not required, the frequency shift caused by mechanical aging is eliminated. After the cavity tuning and welding are completed, there is no need to wait and adjust the tuning, shortening the resonant cavity tuning period, and zero microwave leakage at the connection position can be achieved after passing the vacuum leak detection.

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

[0045] Specifically, the upper cut-off waveguide 210 in the flight area is used to suppress the microwave power frequency shift of the cold atom cloud during free flight caused by the external environmental microwave. The resonator upper cut-off waveguide 310 is used to suppress the microwave power frequency shift of the small hole above the Ramsey resonator 100 during the free flight of the cold atom cloud. The resonator lower cut-off waveguide 320 is used to suppress the microwave power leakage of the small hole below the Ramsey resonator 100. The semi-rigid cable 430 is welded to the rectangular waveguide 410 using lead-free solder, and is used to feed the excitation microwave of the frequency synthesis system into the rectangular waveguide 410.

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

[0047] The Ramsey cavity is provided with small holes to facilitate the cold atom cloud to pass through the cavity twice during upward and downward throwing, so as to realize Ramsey transition. The existence of the small holes in the cavity destroys the circular waveguide structure characteristics of the two ends of the cylindrical cavity, resulting in the microwave flowing out of the small holes and causing microwave leakage. Therefore, the small holes of the Ramsey resonator need to be designed. By designing a cut-off waveguide at the small holes, the small holes can not only meet the need for the cold atom cloud to pass through the cavity, but also suppress the microwave leakage in the cavity.

[0048] Multiple modes can exist in the circular waveguide. Among them, the fundamental mode is the TE11 mode, and the frequency of this mode is the cut-off frequency. When the excitation microwave frequency is lower than the cut-off frequency, the excitation microwave is an evanescent wave, and the field components decay rapidly in an exponential form in the waveguide, which can realize the function of cutting off the propagation of the excitation microwave. The cut-off frequency and the attenuation rate are related to the small hole diameter, and the total attenuation is the result of the combined action of the small hole diameter and the waveguide length. The circular waveguide is designed at the small hole position to make the microwave in the cavity decay rapidly and suppress the microwave leakage. Therefore, this circular waveguide is called a cut-off waveguide.

[0049] Exemplarily, for a Cs atomic fountain clock, the excitation microwave frequency is 9.192631770 GHz, and the maximum inner diameter of the corresponding cutoff waveguide in a vacuum environment is 19.1 mm. In the design, with a 5% margin, the designed minimum cutoff frequency of the cutoff waveguide is greater than 9.68 GHz, the corresponding inner diameter is 18.2 mm, and the attenuation rate is 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 length of the cutoff waveguide required to achieve the same cutoff effect. For a Cs atomic fountain clock, on the premise of ensuring that the cold atom cloud passes through the cavity, the inner diameter of the cutoff waveguide 300 can be set to 10 mm to 14 mm, and the total length is greater than 60 mm. The length and size of this cutoff waveguide 300 are also suitable for the upper cutoff waveguide 210 in the flight area to suppress the influence of external free microwaves.

[0050] Exemplarily, for an Rb atomic fountain clock, the excitation microwave frequency is 6.8346826 GHz, and the maximum radius of the corresponding cutoff waveguide in a vacuum environment is 25.7 mm. In the design, with a 5% margin, the designed minimum cutoff frequency of the cutoff waveguide is greater than 7.18 GHz, the corresponding inner diameter is 24.5 mm, and the attenuation rate is 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 length of the cutoff waveguide required to achieve the same cutoff effect. For an Rb atomic fountain clock, on the premise of ensuring that the cold atom cloud passes through the cavity, the inner diameter of the cutoff waveguide 300 can be set to 12 mm to 18 mm, and the length is greater than 60 mm. The length and size of this cutoff waveguide 300 are also suitable for the upper cutoff waveguide 210 in the flight area to suppress the influence of external free microwaves.

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

[0052] Taking cesium atoms (Cs) as an example, the working process of a cold atom fountain clock including the fully welded Ramsey microwave resonator of the present invention is as follows:

[0053] S1. Cs atomic vapor in the vacuum cavity is cooled by laser to form a cold atom cloud, and Cs atoms are evenly distributed on each m F sub-energy level of |F = 4>. Subsequently, the cold atom cloud is thrown upward by using the moving optical molasses technique. After the cold atom cloud leaves the cold atom preparation area, it sequentially passes through the state selection cavity, the fluorescence collection and detection area, the Ramsey cavity and the free flight area, and then returns to the Ramsey cavity to complete the entire Ramsey working process;

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

[0055] S3. The Cs atoms continue to rise, and in the fluorescence collection and detection area between the state selection cavity and the lower cut-off waveguide 320 of the resonant cavity, the repulsion light removes the atoms at the energy level of |F = 4, m F ≠ 0>, and only the atoms with |F = 3, m F = 0> are retained;

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

[0057] S5. The Cs atoms leave the Ramsey resonant cavity 100 and fly freely, gradually decelerating to zero and reaching a certain maximum height within the flight area waveguide 200. Subsequently, under the action of gravity, they start to fall back and pass through the Ramsey resonant cavity 100 for the second time. Under the action of the second π / 2 pulse of the second microwave field having the second microwave power, the atoms complete the entire Ramsey process, and the atomic population is inverted to the energy level of |F = 4, m F = 0>;

[0058] S6. The cold atom clump falls back to the detection area between the Ramsey resonant cavity 100 and the state selection cavity. Under the action of the probe light 1, the repulsion light, and the probe light 2, the fluorescence collectors 1 and 2 detect the fluorescence generated by the atoms at the energy levels of |F = 4, m F = 0> and |F = 3, m F = 0>. Among them, the fluorescence collectors 1 and 2 are two sets of fluorescence collection devices in the fluorescence collection and detection area for detecting the hyperfine energy level population of Cs atoms. Thus, the population of Cs atoms at the energy levels of |F = 4, m F = 0> and |F = 3, m F = 0> is obtained, and thus the entire quantum part of the Cs fountain clock working process is completed.

[0059] The fully welded Ramsey microwave resonator for a cold atom fountain clock according to the present invention realizes an integrated structure of the entire cavity through an integral welding process, completely eliminating the hidden danger of microwave leakage caused by the difference in thermal expansion of materials in traditional indium wire seals and titanium alloy fasteners. After welding, repeated debugging is no longer required, reducing the tuning period of the resonator, and it is especially suitable for low-temperature working environment scenarios. At the same time, through the non-closed atomic free flight channel, it is convenient for the vacuum system to maintain a high vacuum state in the flight area, reducing the loss of cold atom clusters and resulting in a larger atomic signal.

[0060] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements but also other elements not explicitly listed. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the article or device including the said element. Terms such as "connected" or "coupled" do not limit to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The orientation or positional relationship indicated by "up", "down", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0061] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A fully welded Ramsey microwave resonant cavity for a cold atomic fountain clock, characterized in that: include: A Ramsey resonant cavity (100), a flight zone waveguide (200), a cutoff waveguide (300) and a microwave feeding system (400), wherein: The flight zone waveguide (200) is arranged above the Ramsey resonant cavity (100), and the top of the flight zone waveguide (200) forms a non-enclosed 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; and the microwave feeding system (400) is integrally connected to the Ramsey resonant cavity (100).

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

3. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 1, characterized in that: The flight zone waveguide (200) comprises: a flight zone upper cutoff waveguide (210) and a flight zone waveguide tube (220) connected in sequence from top to bottom, the flight zone upper cutoff waveguide (210) and the flight zone waveguide tube (220) are an integrated structure, and the flight zone waveguide tube (220) is connected to the cutoff waveguide (300) by welding.

4. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 3, characterized in that: The diameter of the flight zone upper cutoff waveguide (210) is smaller than the diameter of the flight zone waveguide tube (220).

5. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 3, characterized in that: The cutoff waveguide (300) comprises: an upper cutoff waveguide (310) of the resonant cavity and a lower cutoff waveguide (320) of the resonant cavity, wherein 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 integrated structure with the Ramsey resonant cavity (100); and the lower cutoff waveguide (320) of the resonant cavity is connected to the second end of the Ramsey resonant cavity (100), and forms an integrated structure with the Ramsey resonant cavity (100).

6. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 5, characterized in that: The microwave feeding system (400) comprises 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; the semi-rigid cable (430) is connected to the rectangular waveguide (410) by welding; and the rectangular waveguide (410) and the Ramsey cavity (100) are an integrally machined structure.

7. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 6, 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).

8. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 7, characterized in that: The Ramsey resonant cavity (100), the flight zone upper cutoff waveguide (210), the flight zone waveguide tube (220), the resonant cavity upper cutoff waveguide (310), the resonant cavity lower cutoff waveguide (320), the rectangular waveguide (410) and the 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.

9. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 7, characterized in that: The flight zone waveguide tube (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 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 welding.

10. The fully welded Ramsey microwave resonant cavity for cold atomic fountain clock according to claim 6, characterized in that: The fully welded Ramsey microwave resonant cavity for a cold atomic fountain clock adopts two-stage coupling, wherein the first-stage coupling is coupling the semi-rigid cable (430) to the rectangular waveguide (410), and the second-stage coupling is coupling the rectangular waveguide (410) to the Ramsey resonant cavity (100); wherein the first-stage coupling is electrical coupling, and the second-stage coupling is pinhole coupling.

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