A laser-pumped cesium beam tube

Abstract

This invention provides a laser-pumped cesium beam tube, comprising: a vacuum tube shell and a cesium atomic furnace, a laser frequency stabilization module, a laser pumping module, a microwave module, and a laser detection module disposed within the vacuum tube shell; wherein, the laser frequency stabilization module causes cesium atoms to transition from F=4 to F'=5 and then emit fluorescence back to the F=4 state, collects the first fluorescence signal emitted by the current cesium atom, converts the first fluorescence signal into a first electrical signal, and provides it to the control circuit of the laser system; the laser pumping module causes cesium atoms to transition from F=4 to F'=4 and then emit fluorescence back to the F=3 or F=4 state; the microwave module causes cesium atoms to transition from F=3 and mF=0 to F=4 and mF=0 state; the laser detection module causes cesium atoms to transition from F=4 to F'=5 and then emit fluorescence back to the F=4 state, collects the second fluorescence signal emitted by the current cesium atom as the frequency discrimination signal of the cesium atomic clock. The technical solution provided in this application simplifies the system structure of cesium atomic clocks and significantly improves frequency stability.

Description

Technical Field

[0001] This invention relates to the field of atomic clock technology, and more specifically to a laser-pumped cesium beam tube. Background Technology

[0002] Atomic clocks are currently the most precise timekeeping devices in the world. They utilize the stable electromagnetic wave frequency generated during quantum energy level transitions within atoms as a time standard. The physical principle is that when atoms transition between different energy levels, they absorb or emit electromagnetic waves of specific frequencies. These frequencies are extremely stable and unaffected by external environmental factors, thus serving as a precise time standard. Laser-pumped cesium atomic clocks are high-precision atomic clocks that utilize laser technology for atomic state preparation and detection. They use the inherent frequency of the hyperfine energy level transitions in the ground state of cesium atoms as a time frequency standard, achieving high-precision timekeeping through the resonant interaction between atoms and microwaves.

[0003] The laser-pumped cesium beam tube is a core component of the laser-pumped cesium atomic clock, serving to provide the atomic transition frequency discrimination signal for the cesium atomic clock. Currently, the working process of the laser-pumped cesium beam tube in the cesium atomic clock is as follows: Cesium atoms are pumped and prepared to their ground state energy levels under the action of a pump laser. Subsequently, they are excited by microwaves at a frequency of approximately 9192631770 Hz within a microwave cavity, causing some atoms to undergo ground state sub-level transitions. Finally, under the action of a detection laser, the cyclic transitions of cesium atoms are detected. The detected atomic fluorescence is converted into an electrical signal output, which serves as the frequency discrimination signal for the cesium atomic clock, used to adjust the output frequency of the crystal oscillator of the atomic clock.

[0004] However, in the above process, both the pump laser and the detection laser are generated by lasers within the cesium atomic clock. These lasers are locked onto the saturated absorption spectrum of cesium atoms in the atomic gas chamber, rather than by the laser-pumped cesium beam tube. In other words, the cesium atoms acted upon by the laser in the laser-pumped cesium beam tube and the cesium atoms used to lock the laser in the atomic gas chamber are from "different sources." This leads to two problems: First, collisions between atoms in the cesium atomic gas chamber, and between atoms and the chamber wall, cause atomic energy level shifts and spectral line broadening. This results in a persistent deviation between the final laser locking frequency and the frequency of the cesium atom's F=4 to F'=5 transition spectral line, leading to a decrease in the pumping and detection efficiency of cesium atoms in the cesium beam tube. Second, to maintain a certain atomic density to ensure the amplitude and stability of the saturated absorption spectrum, the cesium atomic gas chamber typically needs to be heated and its temperature controlled in the atmosphere. However, atmospheric disturbances limit the temperature control accuracy to only about 0.1℃, causing fluctuations in the laser locking frequency. Furthermore, cesium atomic clocks often operate in a wide temperature range, and the stability of laser operation deteriorates further when the ambient temperature fluctuates significantly. These two issues limit the improvement of the overall performance of cesium atomic clocks and their operational stability under wide temperature conditions. Currently, lasers use various frequency stabilization methods besides saturated absorption spectroscopy, such as modulation-transfer spectroscopy and polarization spectroscopy, but all of these methods require an additional cesium atomic gas chamber, and the aforementioned problems persist.

[0005] Therefore, how to design a technical solution for laser-pumped cesium bundle tubes to improve the laser locking effect in laser-pumped cesium atomic clocks has become an urgent problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a laser-pumped cesium beam tube, the laser-pumped cesium beam tube comprising: A vacuum tube, comprising: a vacuum tube shell and a cesium atomic furnace, a laser frequency stabilization module, a laser pumping module, a microwave module, and a laser detection module disposed within the vacuum tube shell; The cesium atomic furnace is used to emit a cesium atom beam, which sequentially passes through the laser frequency stabilization module, the laser pumping module, the microwave module, and the laser detection module; wherein... The laser frequency stabilization module is used to inject a frequency-stabilized laser into the vacuum tube shell, causing cesium atoms to transition from F=4 to F'=5 and then emit fluorescence back to the F=4 state. It collects the first fluorescence signal emitted by the cesium atom and converts it into a first electrical signal, which is then provided to the control circuit of the laser system. The control circuit determines whether the intensity of the first electrical signal reaches its maximum value at the center of the cesium atom's F=4 to F'=5 transition spectral line. If not, it adjusts the laser frequency of the original laser to maintain the first electrical signal intensity at its maximum value at the center of the cesium atom's F=4 to F'=5 transition spectral line. The original laser is used to generate the frequency-stabilized laser, the pump laser, and the detection laser. The laser pumping module is used to inject the pumping laser into the vacuum tube shell, causing the cesium atoms to transition from F=4 to F'=4 and then emit fluorescence back to the F=3 or F=4 state. Through the multiple actions of the pumping laser, all the cesium atoms in the F=4 state are eventually pumped to the F=3 state. The microwave module is used to input excitation microwaves into the vacuum tube shell, causing the cesium atom to transition from the F=3 and mF=0 state to the F=4 and mF=0 state. The laser detection module is used to shoot the detection laser into the vacuum tube shell, causing the cesium atom to transition from F=4 to F'=5 and then emit fluorescence back to the F=4 state. The module collects the second fluorescence signal emitted by the current cesium atom and converts the second fluorescence signal into a second electrical signal as the frequency discrimination signal of the cesium atomic clock.

[0007] Optionally, the laser frequency stabilization module includes: a first optical window and a first fluorescence detector; The first optical window is disposed on the housing of the vacuum tube shell, the first fluorescence detector is disposed inside the vacuum tube shell, and the normal direction of the first optical window is perpendicular to the cesium atom beam. The frequency-stabilized laser is incident into the cesium beam tube through the first optical window in a direction perpendicular to the cesium atom beam, and excites the cesium atom beam at the center of the first fluorescence detector. The first fluorescence detector is used to collect the first fluorescence signal emitted by the current cesium atom and convert it into a first electrical signal.

[0008] Optionally, the first fluorescence detector includes: a first concave mirror, a second concave mirror, a photodiode, and a support structure; The support structure is used to fix the first concave reflector, the second concave reflector, and the photodiode; The first concave mirror has a central opening, and the reflective surface is used to reflect the received cesium atom fluorescence onto the second concave mirror; The second concave mirror is used to focus the directly received cesium atom fluorescence and the cesium atom fluorescence reflected from the first concave mirror onto the photodiode; The photosensitive surface of the photodiode is disposed at the opening of the first concave reflector, and is used to convert the first fluorescent signal into a first electrical signal.

[0009] Optionally, the laser pumping module includes: a second optical window; The second optical window is disposed on the housing of the vacuum tube, and the normal direction of the second optical window is perpendicular to the cesium atom beam. The pump laser enters the cesium beam tube through the second optical window in a direction perpendicular to the cesium atom beam and excites the cesium atom beam.

[0010] Optionally, the microwave module includes: a microwave cavity, a magnetic field coil, and a magnetic shielding device; The microwave cavity is disposed inside the vacuum tube shell, and the excitation microwave is input into the microwave cavity from the microwave input port of the microwave cavity, which excites the cesium atom beam passing through the microwave cavity to generate ground state energy level transitions; The magnetic field coil is disposed inside the vacuum tube shell and is used to generate a weak magnetic field to provide a quantization axis for the cesium atom, causing the energy level of the cesium atom to undergo Zeeman splitting; The magnetic shielding device is disposed inside the vacuum tube shell.

[0011] Optionally, the laser detection module includes: a third optical window and a second fluorescence detector; The third optical window is disposed on the shell of the vacuum tube, the second fluorescence detector is disposed inside the vacuum tube, and the normal direction of the third optical window is perpendicular to the cesium atom beam. The detection laser passes through the third optical window and is incident into the cesium beam tube in a direction perpendicular to the cesium atom beam, and is excited by the cesium atom beam at the center of the second fluorescence detector. The second fluorescence detector is used to collect the second fluorescence signal and convert it into a second electrical signal, which serves as the frequency discrimination signal for the entire device.

[0012] Optionally, the laser-pumped cesium beam tube further includes a laser optical path system, which is disposed outside the vacuum housing and is used to emit the original laser and split the original laser into a frequency-stabilized laser, a pump laser, and a detection laser.

[0013] Optionally, the laser optical path system includes: a laser, a first polarizing beam splitter, a second polarizing beam splitter, and an acousto-optic modulator; The original laser emitted by the laser is split by the first polarizing beam splitter to form a first laser and a second laser. The first laser path is used to form the frequency-stabilized laser; The second laser beam is split by the second polarizing beam splitter to form the third and fourth laser beams; The third laser beam is frequency-shifted by the acousto-optic modulator to form the pump laser; The fourth laser beam is used to generate the detection laser.

[0014] Optionally, the laser optical path system further includes: an isolator, a first half-wave plate, a second half-wave plate, a first beam expander, a second beam expander, and a third beam expander; The original laser emitted by the laser is sequentially adjusted by the isolator and the first half-wave plate, and then split by the first polarizing beam splitter. After the first laser beam is adjusted by the first beam expander, it forms the frequency-stabilized laser. The second laser beam, after being adjusted by the second half-wave plate, is split by the second polarizing beam splitter. The third laser beam is sequentially adjusted by the acousto-optic modulator and the second beam expander to form the pump laser. The fourth laser beam, after being adjusted by the third beam expander, forms the detection laser.

[0015] Optionally, the laser optical path system further includes a reflector for adjusting the irradiation direction of the frequency-stabilized laser, the pump laser, and the detection laser to be perpendicular to the cesium atom beam.

[0016] The technical solution provided in this application establishes an independent laser frequency stabilization module. It utilizes a frequency-stabilized laser to generate independent F'=5 to F=4 fluorescence signals from homologous cesium atoms within a cesium beam tube for laser frequency stabilization. Simultaneously, through a collision-free atomic beam in a vacuum environment, multi-layer magnetic shielding, and a vertical optical path design, it achieves more stable atomic spectral lines. Furthermore, this application can utilize F=4 to F'=5 cyclic transitions to enhance the intensity of the fluorescence signal, eliminate frequency difference problems, and improve pump detection efficiency. Ultimately, it simplifies the system structure, enhances vibration resistance, reduces costs, and significantly improves the overall frequency stability.

[0017] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the structure of the laser-pumped cesium beam tube provided in the embodiments of this application; Figure 2This is a schematic diagram of the fluorescence detector setup provided in an embodiment of this application; Figure 3 A schematic diagram illustrating the changes in cesium atomic energy levels involved in the operation of a laser-pumped cesium beam tube, provided in an embodiment of this application. Figure 4 This is a schematic diagram of the fluorescence signals of cesium atoms F'=5 to F=4 used to lock the laser frequency, provided in an embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 100-Vacuum tube; 110-Vacuum tube shell; 120-Cesium atomic furnace; 130-Laser frequency stabilization module; 131-First optical window; 132-First fluorescence detector; 1321-First concave mirror; 1322-Second concave mirror; 1323-Photodiode; 140-Laser pump module; 141-Second optical window; 150-Microwave module; 151-Microwave cavity; 152-Magnetic field coil; 153-Magnetic shielding device; 160-Laser detection module; 161-Third optical window; 162-Second fluorescence detector; 200 - Laser optical path system; 210 - Laser; 221 - First polarizing beam splitter; 222 - Second polarizing beam splitter; 230 - Acousto-optic modulator; 240 - Isolator; 251 - First half-wave plate; 252 - Second half-wave plate; 261 - First beam expander; 262 - Second beam expander; 263 - Third beam expander; 271 - First reflecting mirror; 272 - Second reflecting mirror; 273 - Third reflecting mirror. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] This application provides a laser-pumped cesium beam tube, such as Figure 1 As shown, the laser-pumped cesium beam tube includes a vacuum tube 100. The vacuum tube 100 includes a vacuum tube shell 110 and a cesium atomic furnace 120, a laser frequency stabilization module 130, a laser pumping module 140, a microwave module 150, and a laser detection module 160 arranged sequentially within the vacuum tube shell 110 along the cesium atomic beam emission direction.

[0022] The cesium atom furnace 120 emits a cesium atom beam, which passes sequentially through a laser frequency stabilization module 130, a laser pump module 140, a microwave module 150, and a laser detection module 160 within a vacuum tube 110. The laser frequency stabilization module 130 directs a frequency-stabilized laser beam into the vacuum tube 110, causing it to act on the cesium atom beam. The laser pump module 140 directs a pump laser beam into the vacuum tube 110, causing it to act on the cesium atom beam. The microwave module 150 inputs excitation microwaves into the vacuum tube 110, causing them to act on the cesium atom beam. The laser detection module 160 directs a detection laser beam into the vacuum tube 110, causing it to act on the cesium atom beam. The frequency-stabilized laser, pump laser, and detection laser are all formed by splitting the original laser emitted by the laser generator.

[0023] For the cesium atom, its ground state electronic configuration is 6S. 1 / 2 The total angular momentum quantum number of the electron is J = 1 / 2. The spin quantum number of the cesium nucleus is I = 7 / 2. The total angular momentum J of the electron couples with the nuclear spin angular momentum I to form the total angular momentum of the atom, i.e., the hyperfine structure total angular momentum quantum number F, which ranges from |IJ| to I+J. The cesium atom is in its ground state (6S). 1 / 2 When F=3 or F=4, the cesium atom is in an excited state (6P). 3 / 2 When F'=2, F'=3, F'=4, or F'=5, the laser has the characteristics of good monochromaticity, strong coherence, and high brightness. It can provide a large number of photons with energy precisely matching the energy level difference of cesium atoms, driving cesium atoms from the ground state to the excited state through stimulated absorption. Cesium atoms in the excited state are unstable and will couple with quantum vacuum fluctuations, thus releasing photons in the form of spontaneous emission, randomly jumping back to a lower energy state. In the spontaneous emission process of electric dipole transition, it must obey the selection rule between hyperfine energy levels: ΔF = 0, ±1.

[0024] Based on the above principle, the laser frequency stabilization module 130 is used to inject a frequency-stabilized laser into the vacuum tube shell 110. The frequency of the frequency-stabilized laser is set to the center frequency of the spectral line at which cesium atoms transition from F=4 to F'=5. The cesium atom beam emitted from the cesium atom furnace 120, under the action of the frequency-stabilized laser, causes the cesium atoms to transition from F=4 to F'=5, then spontaneously emit fluorescence before returning to the F=4 state.

[0025] Here, if the frequency-stabilized laser is locked onto the transition center from F=4 to F'=5 in a cesium atom, the frequency of the stabilized laser is precisely aligned with the resonance frequency of the electron transition inside the cesium atom. At this point, the atom absorbs the strongest light, and the emitted fluorescence intensity is the highest. Conversely, if the frequency-stabilized laser deviates from the center frequency of the spectral line of the F=4 to F'=5 transition in the cesium atom, the emitted fluorescence intensity will not reach its maximum. Therefore, the observed fluorescence intensity can be used as a reference for laser frequency stabilization. Laser frequency stabilization here can be understood as a dynamic equilibrium process: finding a stable atomic reference frequency, comparing the frequency of the laser diode with this reference frequency in real time, and adjusting the frequency back through a feedback mechanism when a deviation is detected.

[0026] The laser frequency stabilization module 130 collects the first fluorescence signal emitted by the cesium atoms at this time, converts the first fluorescence signal into a first electrical signal, and provides it to the control circuit in the laser system. The control circuit determines whether the intensity of the first electrical signal reaches the maximum value at the center of the cesium atom F=4 to F'=5 transition spectral line. If it does not reach the maximum value, the control circuit adjusts the laser frequency of the original laser to maintain the first electrical signal intensity at the maximum value at the center of the cesium atom F=4 to F'=5 transition spectral line, thereby locking the frequency of the original laser at the frequency of the cesium atom F=4 to F'=5 transition spectral line, thus ensuring that the pump laser and the detection laser separated from the original laser are at their respective required frequencies. In the actual frequency stabilization control process, the laser control part modulates the laser to determine whether the laser frequency is too low or too high, in order to achieve the frequency stabilization control process. This is a common control method known to those skilled in the art.

[0027] It should be noted that this application uses the cyclic transition spectral lines of cesium atoms from F=4 to F'=5 as the laser frequency stabilization reference spectral lines. During the atomic leap beam process, a single atom can generate hundreds of photons, while when other non-cyclic transitions are used, such as F=4 to F'=4, a single atom can only generate about two photons on average. Therefore, the cyclic transition reference spectral lines used in this application have a very strong signal intensity, which can play a very good role in subsequent frequency stabilization.

[0028] The laser pump module 140 is used to inject a pump laser into the vacuum tube shell 110. The pump laser is a beam split from the original laser beam whose frequency has been locked to the frequency of the spectral line from F=4 to F'=5 of cesium atoms. Its frequency is shifted by an acousto-optic modulator to the frequency of the spectral line from F=4 to F'=4 of cesium atoms. After being subjected to the frequency-stabilized laser, the cesium atom beam returns to the ground state of all atoms due to the short lifetime of the excited state F'=5, maintaining the same state as when it was first emitted from the cesium atom furnace 120. Under the action of the pump laser, cesium atoms transition from F=4 to F'=4 and then emit fluorescence back to the F=3 or F=4 state. Cesium atoms in the F=4 state will be excited again to F'=4. During the process of jumping the pump beam, through multiple actions, the number of cesium atoms in the F=4 energy level gradually decreases, and eventually all cesium atoms accumulate in the F=3 ground state energy level. In other words, through multiple pump laser cycles, all cesium atoms in the F=4 state are eventually pumped to the F=3 state. When all cesium atoms are in the F=3 ground state energy level, the pumping preparation of the cesium atom ground state energy level is completed.

[0029] The microwave module 150 is used to input excitation microwaves into the vacuum tube housing 110. The frequency of the excitation microwaves is approximately 9192631770 Hz. The cesium atoms in the pumped laser-excited cesium atom beam have a certain probability of transitioning from the state F=3 and mF=0 to the state F=4 and mF=0 under the influence of the excitation microwaves, where mF represents the magnetic quantum number.

[0030] The laser detection module 160 is used to direct a detection laser into the vacuum tube 110. The detection laser is a beam split after frequency stabilization, with its frequency locked to the spectral line frequency of the cesium atom transitioning from F=4 to F'=5. After excitation by microwave, cesium atoms transitioning to the F=4 and mF=0 state are cyclically detected by the laser. The emitted second fluorescence signal is collected by the laser detection module 160 and converted into a second electrical signal as the frequency discrimination signal for the cesium atomic clock. Based on this frequency discrimination signal, the atomic clock control circuit can adjust the output frequency of its crystal oscillator to lock it at the intrinsic transition frequency of the cesium atom, forming a closed loop, and ultimately outputting a standard time and frequency signal that combines the short-term stability of the crystal oscillator with the long-term accuracy of the atom.

[0031] In a preferred embodiment, the laser frequency stabilization module 130 includes a first optical window 131 and a first fluorescence detector 132. The first optical window 131 is disposed on the housing of the vacuum tube 110, and the first fluorescence detector 132 is disposed inside the vacuum tube 110, with the normal direction of the first optical window 131 perpendicular to the cesium atom beam. The frequency-stabilized laser enters the cesium beam tube through the first optical window 131 in a direction perpendicular to the cesium atom beam, and at the center of the first fluorescence detector 132, it excites the cesium atom beam emitted from the cesium atom furnace 120. The first fluorescence detector 132 collects the first fluorescence signal emitted by the current cesium atoms and converts the first fluorescence signal into an electrical signal, which is then sent to the control circuit of the laser system.

[0032] In a preferred embodiment, such as Figure 2 As shown, the first fluorescence detector 132 includes: a first concave mirror 1321, a second concave mirror 1322, a photodiode 1323, and a support structure (not shown in the figure). The support structure is used to fix the first concave mirror 1321, the second concave mirror 1322, and the photodiode 1323. The first concave mirror 1321 has an opening at its center, which is used to house the photosensitive surface of the photodiode 1323. The reflective surface of the first concave mirror 1321 reflects the received cesium atomic fluorescence onto the second concave mirror 1322. The second concave mirror 1322 focuses the cesium atomic fluorescence received by its own reflective surface and the cesium atomic fluorescence reflected from the first concave mirror 1321 onto the photodiode 1323. The photodiode 1323 converts the first fluorescence signal into a first electrical signal.

[0033] In a preferred embodiment, the laser pumping module 140 includes a second optical window 141. The second optical window 141 is disposed on the housing of the vacuum tube 110, and the normal direction of the second optical window 141 is perpendicular to the cesium atom beam. The pumping laser enters the cesium beam tube through the second optical window 141 in a direction perpendicular to the cesium atom beam and is excited by the cesium atom beam.

[0034] In a preferred embodiment, the microwave module 150 includes a microwave cavity 151, a magnetic field coil 152, and a magnetic shielding device 153.

[0035] The microwave cavity 151 is disposed within the vacuum tube shell 110 and has a microwave input port. Excitation microwaves are input into the microwave cavity 151 through the input port, stimulating the cesium atom beam passing through the microwave cavity 151 to generate a ground-state energy level transition. A magnetic field coil 152 is disposed within the vacuum tube shell 110 along the direction of the cesium atom beam, and a magnetic shielding device 153 is disposed between the magnetic field coil 152 and the vacuum tube shell 110. The magnetic field coil 152 is used to generate approximately 6 × 10⁻⁶... -6Tesla's uniform weak magnetic field provides a quantization axis for cesium atoms and causes Zeeman splitting of the energy levels of these atoms, separating the mF=0 state. The magnetic shielding device 153 serves to shield stray magnetic fields, including the Earth's magnetic field, and to keep the weak magnetic field generated by the magnetic field coil 152 undisturbed.

[0036] In a preferred embodiment, the laser detection module 160 includes a third optical window 161 and a second fluorescence detector 162. The third optical window 161 is disposed on the housing of the vacuum tube 110, and the second fluorescence detector 162 is disposed inside the vacuum tube 110. The normal direction of the third optical window 161 is perpendicular to the cesium atom beam. The detection laser passes through the third optical window 161 and is incident into the cesium beam tube perpendicular to the cesium atom beam, where it excites the cesium atom beam at the center of the second fluorescence detector 162. The second fluorescence detector 162 collects the second fluorescence signal emitted by the current cesium atoms and converts the second fluorescence signal into a second electrical signal. Here, the second fluorescence detector 162 can have the same structure as the first fluorescence detector 132, and those skilled in the art can adjust the size of the two fluorescence detectors as needed.

[0037] In addition, the laser-pumped cesium beam tube provided in this application also includes a laser optical path system 200 for providing the aforementioned frequency-stabilized laser, pump laser, and detection laser. The laser optical path system 200 includes a laser 210, a first polarizing beam splitter 221, a second polarizing beam splitter 222, and an acousto-optic modulator 230. The laser 210 is used to emit the original laser light, the polarizing beam splitter is used to separate the incident light according to its polarization state, and the acousto-optic modulator 230 is used for laser frequency shifting.

[0038] In the optical path of the laser optical path system 200, the laser 210 is in a free-running state when it is first powered on, and its frequency is unstable. The original laser emitted by the laser is split by the first polarizing beam splitter 221 to form a first laser and a second laser. The first laser is used to form a frequency-stabilized laser. The first fluorescence signal generated by the cesium atoms excited by this frequency-stabilized laser is used as a reference. The frequency of the original laser is locked by the control circuit to the transition line from F=4 to F'=5 of the cesium atom. The second laser is split again by the second polarizing beam splitter 222 to form a third laser and a fourth laser. The third laser is frequency-shifted by the acousto-optic modulator 230 to form a pump laser with the same frequency as the transition line from F=4 to F'=4 of the cesium atom. The fourth laser is not frequency-shifted and is used to form a detection laser with the same frequency as the original laser.

[0039] Thus, by rationally arranging the beam-splitting nodes, this application achieves the required settings for frequency-stabilized lasers, pump lasers, and detection lasers without adding a large number of additional components. Furthermore, debugging multiple laser paths during the overall commissioning of an atomic clock is extremely cumbersome. This application simplifies the optical path of the laser system, making the laser optical path system 200 very small. It can be integrated with the vacuum tube 100 onto the laser-pumped cesium beam tube, which facilitates the miniaturization of the integrated equipment and supports mass production.

[0040] In a preferred embodiment, the laser optical path system 200 further includes: an isolator 240, a first half-wave plate 251, a second half-wave plate 252, a first beam expander 261, a second beam expander 262, and a third beam expander 263. The isolator 240 enables unidirectional laser conduction, the half-wave plate (λ / 2 wave plate) works in conjunction with a polarizing beam splitter to achieve intensity modulation, and the beam expander extends the beam diameter to cover an atomic beam, enabling efficient utilization of atoms.

[0041] The original laser emitted by laser 210 is sequentially adjusted by isolator 240 and first half-wave plate 251, and then split into a first laser and a second laser by first polarizing beam splitter 221. The first laser is then adjusted by first beam expander 261 to form a frequency-stabilized laser. The second laser is adjusted by second half-wave plate 252 and then split into a third laser and a fourth laser by second polarizing beam splitter 222. The third laser is sequentially frequency-shifted by acousto-optic modulator 230 and adjusted by second beam expander 262 to form a pump laser. The fourth laser is adjusted by third beam expander 263 to form a detection laser.

[0042] In a preferred embodiment, the laser optical path system 200 further includes a reflector for adjusting the irradiation direction of the frequency-stabilized laser, the pump laser, and the detection laser to be perpendicular to the cesium atom beam.

[0043] In one specific embodiment, the reflector includes a first reflector 271, a second reflector 272, and a third reflector 273. The laser 210 emits the original laser beam in a direction parallel to the direction in which the cesium atom beam is emitted by the cesium atom furnace 120. A first polarizing beam splitter 221 splits the original laser beam, separating a first laser beam perpendicular to the cesium atom beam, while a second laser beam remains parallel to the cesium atom beam, thus allowing the frequency-stabilized laser formed by the first laser beam to interact with the cesium atom beam in a direction perpendicular to the cesium atom beam. A second polarizing beam splitter 222 splits the second laser beam, separating a third laser beam perpendicular to the cesium atom beam, while a fourth laser beam remains parallel to the cesium atom beam. Here, although the direction of the third laser is perpendicular to the cesium atom beam, since the pump laser needs to act in front of the microwave cavity 151, and the acousto-optic modulator 230 and the second beam expander 262 also occupy a certain space in the optical path, two reflectors are set here. This ensures the optical path length is sufficient for arranging the corresponding components while allowing the entrance of the pump laser to correspond to the position of the already set second optical window 141. That is, the third laser is first deflected by the first reflector 271, then passes through the acousto-optic modulator 230 and the second beam expander 262, and is then deflected again by the second reflector 272, forming a pump laser that is still perpendicular to the cesium atom beam. The fourth laser is first deflected by the third reflector 273 to be perpendicular to the cesium atom beam, and then adjusted by the third beam expander 263 to form a detection laser perpendicular to the cesium atom beam. Thus, the frequency-stabilized laser, the pump laser, and the detection laser are all perpendicular to the cesium atom beam.

[0044] The cesium bundle tube provided in this application can achieve at least the following effects: First, the cesium atomic furnace, the emission source for generating the cesium atomic beam, operates in a vacuum environment, making it less affected by changes in ambient temperature. Its temperature control precision can reach the mK level, which is more than an order of magnitude higher than the temperature control precision of an atomic gas chamber operating in atmospheric conditions. Therefore, the atomic spectral line signals used for laser frequency locking are also more stable. When the cesium clock operates over a wide temperature range, its laser system exhibits even greater stability, and the overall frequency stability of the system is also higher.

[0045] Second, there are no collisions between atoms in the cesium atom beam, avoiding spectral shifts caused by collisions. The atoms are enclosed in multiple layers of magnetic shielding, minimizing interference from external magnetic fields and resulting in more stable spectral lines. The laser frequency stabilization module is located at the cesium atom emission port, utilizing the largest number of cesium atoms. Furthermore, the laser is perpendicular to the atomic beam, meaning all atoms contribute to the fluorescence signal, resulting in a high fluorescence signal intensity. In contrast, atoms in the atomic gas chamber exhibit motion in all directions, and only those atoms perpendicular to the laser contribute to the signal intensity of the saturation absorption spectrum.

[0046] Third, the transition from F=4 to F'=5 in cesium atoms is a cyclic transition. Under the action of a frequency-stabilized laser, the atom will repeatedly absorb and emit photons. The fluorescence signal generated by a single atom can be two orders of magnitude higher than that of the F=4→F'=4 transition, and the stability of laser locking is better.

[0047] Fourth, the atoms used to lock the laser and the atoms that the laser is intended to pump and detect are "of the same origin," which fundamentally solves the frequency difference problem, improves the pumping and detection efficiency, and thus improves the frequency stability index of the entire cesium clock.

[0048] Fifth, using the fluorescence signal of the cesium beam tube to stabilize the laser output frequency can avoid the defects of saturated absorption frequency stabilization, simplify the structure of the laser optical path system in the laser-pumped cesium clock, and eliminate the atomic gas chamber and its heating, temperature control and heat preservation devices, which helps to improve the overall vibration resistance of the cesium clock and further reduce costs.

[0049] Sixth, it simplifies the optical path of the laser system, allowing the laser optical path system to be integrated with the vacuum tube onto the laser-pumped cesium beam tube. This facilitates the miniaturization of the integrated equipment and supports mass production. In addition to improving the overall performance of the atomic clock, using the cesium beam tube provided in this application can also simplify optical path debugging and reduce the overall size of the atomic clock.

[0050] The working process of the laser-pumped cesium beam tube described above will be explained below in a specific embodiment.

[0051] A cesium atom beam is generated by heating in a cesium atom furnace 120. At this point, the cesium atoms are distributed in the two ground state energy levels of F=3 and F=4. Simultaneously, a laser emits a primary laser beam, which is then split into a frequency-stabilized laser, a pump laser, and a detection laser. After a period of time, once the cesium atom beam has stabilized, the cyclic transitions of cesium atoms are detected first under the action of the frequency-stabilized laser, utilizing the cyclic transition process where the F'=5 excited state can only fall back to the F=4 ground state. The detected atomic fluorescence is converted into a first electrical signal output, which serves as a reference signal to lock the frequency of the primary laser onto the F=4 to F'=5 transition line. Subsequently, under the action of the pump laser with a frequency at the F=4 to F'=4 transition line of cesium atoms, the pump preparation of the cesium atom ground state energy level is completed by utilizing the transition process where the F'=4 excited state falls back to the F=4 or F=3 ground state, ensuring that all cesium atoms are in the F=3 ground state energy level. Subsequently, under microwave excitation at a frequency of approximately 9192631770 Hz within the microwave cavity, some atoms undergo sub-level transitions from the ground state F=3, mF=0 to F=4, mF=0. Finally, in the detection region, under the action of a detection laser whose frequency is locked to the cesium atom's F=4 to F'=5 transition spectrum, the cyclic transition process of the F'=5 excited state falling back to the F=4 ground state is used to detect the cyclic transitions of cesium atoms. The detected atomic fluorescence is then converted into a second electrical signal output, serving as the frequency discrimination signal for the cesium atomic clock. The cesium atom energy level transition processes involved in the above process are as follows: Figure 3 As shown. The morphology of the fluorescence signals of cesium atoms F'=5 to F=4 used to lock the laser frequency is as follows. Figure 4 As shown.

[0052] In an evaluation of experimental results, compared to traditional saturated absorption frequency stabilization schemes, the cesium beam tube provided in this application improved the frequency stability of the laser-pumped cesium atomic clock from approximately 1.2E-11 / τ. 1 / 2 ~6E-12 / τ 1 / 2 Increased to 2E-12 / τ 1 / 2 (1~100000s), the temperature range where the temperature coefficient satisfies ≤2E-14 / ℃ is extended from 18~28℃ to 0~40℃, and the adaptability to wide temperature environments is significantly improved.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser-pumped cesium beam tube, characterized in that, The laser-pumped cesium beam tube includes: Vacuum tube (100), the vacuum tube (100) includes: vacuum tube shell (110) and cesium atomic furnace (120), laser frequency stabilization module (130), laser pumping module (140), microwave module (150) and laser detection module (160) disposed in the vacuum tube shell (110). The cesium atomic furnace (120) is used to emit a cesium atomic beam, which passes sequentially through the laser frequency stabilization module (130), the laser pump module (140), the microwave module (150), and the laser detection module (160); wherein, The laser frequency stabilization module (130) is used to inject a frequency-stabilized laser into the vacuum tube shell (110), causing cesium atoms to transition from F=4 to F'=5 and then emit fluorescence back to the F=4 state. It collects the first fluorescence signal emitted by the current cesium atom, converts the first fluorescence signal into a first electrical signal, and provides it to the control circuit of the laser system. The control circuit determines whether the intensity of the first electrical signal reaches the maximum value at the center of the cesium atom's F=4 to F'=5 transition spectral line. If it does not reach the maximum value, the laser frequency of the original laser is adjusted to maintain the intensity of the first electrical signal at the maximum value at the center of the cesium atom's F=4 to F'=5 transition spectral line. The original laser is used to generate the frequency-stabilized laser, pump laser, and detection laser. The laser pumping module (140) is used to inject the pumping laser into the vacuum tube shell (110), causing the cesium atoms to transition from F=4 to F'=4 and then emit fluorescence back to the F=3 or F=4 state. Through the multiple actions of the pumping laser, the cesium atoms in the F=4 state are finally all pumped to the F=3 state. The microwave module (150) is used to input excitation microwaves into the vacuum tube shell (110) to cause the cesium atom to transition from F=3 and mF=0 to F=4 and mF=0. The laser detection module (160) is used to shoot the detection laser into the vacuum tube shell (110), causing the cesium atom to transition from F=4 to F'=5 and then emit fluorescence back to the F=4 state. The module collects the second fluorescence signal emitted by the current cesium atom and converts the second fluorescence signal into a second electrical signal as the frequency discrimination signal of the cesium atomic clock.

2. The laser-pumped cesium beam tube according to claim 1, characterized in that, The laser frequency stabilization module (130) includes: a first optical window (131) and a first fluorescence detector (132); The first optical window (131) is disposed on the housing of the vacuum tube (110), the first fluorescence detector (132) is disposed inside the vacuum tube (110), and the normal direction of the first optical window (131) is perpendicular to the cesium atom beam. The frequency-stabilized laser enters the cesium beam tube through the first optical window (131) in a direction perpendicular to the cesium atom beam, and is excited by the cesium atom beam at the center of the first fluorescence detector (132). The first fluorescence detector (132) is used to collect the first fluorescence signal emitted by the current cesium atom and convert it into a first electrical signal.

3. The laser-pumped cesium beam tube according to claim 2, characterized in that, The first fluorescence detector (132) includes: a first concave mirror (1321), a second concave mirror (1322), a photodiode (1323), and a support structure; The support structure is used to fix the first concave mirror (1321), the second concave mirror (1322), and the photodiode (1323). The first concave mirror (1321) has a central opening, and the reflective surface is used to reflect the received cesium atom fluorescence onto the second concave mirror (1322); The second concave mirror (1322) is used to focus the directly received cesium atomic fluorescence and the cesium atomic fluorescence reflected from the first concave mirror (1321) onto the photodiode (1323). The photosensitive surface of the photodiode (1323) is disposed at the opening of the first concave reflector (1321) and is used to convert the first fluorescent signal into a first electrical signal.

4. The laser-pumped cesium beam tube according to claim 1, characterized in that, The laser pumping module (140) includes: a second optical window (141); The second optical window (141) is disposed on the housing of the vacuum tube (110), and the normal direction of the second optical window (141) is perpendicular to the cesium atom beam. The pump laser enters the cesium beam tube through the second optical window (141) in a direction perpendicular to the cesium atom beam and is excited by the cesium atom beam.

5. The laser-pumped cesium beam tube according to claim 1, characterized in that, The microwave module (150) includes: a microwave cavity (151), a magnetic field coil (152), and a magnetic shielding device (153). The microwave cavity (151) is disposed inside the vacuum tube shell (110). The excitation microwave is input from the microwave input port of the microwave cavity (151) into the microwave cavity (151) to excite the cesium atom beam passing through the microwave cavity (151) to generate ground state energy level transition. The magnetic field coil (152) is disposed inside the vacuum tube shell (110) to generate a weak magnetic field, provide a quantization axis for the cesium atom, and cause the energy level of the cesium atom to undergo Zeeman splitting; The magnetic shielding device (153) is disposed inside the vacuum tube shell (110).

6. The laser-pumped cesium beam tube according to claim 1, characterized in that, The laser detection module (160) includes: a third light window (161) and a second fluorescence detector (162); The third optical window (161) is disposed on the housing of the vacuum tube (110), and the second fluorescence detector (162) is disposed inside the vacuum tube (110). The normal direction of the third optical window (161) is perpendicular to the cesium atom beam. The detection laser passes through the third optical window (161) and is incident into the cesium beam tube in a direction perpendicular to the cesium atom beam. The laser excites the cesium atom beam at the center of the second fluorescence detector (162). The second fluorescence detector (162) is used to collect the second fluorescence signal and convert it into a second electrical signal, which serves as the frequency discrimination signal for the whole machine.

7. The laser-pumped cesium beam tube according to any one of claims 1-6, characterized in that, The laser-pumped cesium beam tube also includes: a laser optical path system (200); The laser optical path system (200) is located outside the vacuum housing (110) and is used to emit the original laser and split the original laser into a frequency-stabilized laser, a pump laser and a detection laser.

8. The laser-pumped cesium beam tube according to claim 7, characterized in that, The laser optical path system (200) includes: a laser (210), a first polarizing beam splitter (221), a second polarizing beam splitter (222), and an acousto-optic modulator (230). The original laser emitted by the laser (210) is split by the first polarizing beam splitter (221) to form a first laser and a second laser. The first laser path is used to form the frequency-stabilized laser; The second laser beam is split by the second polarizing beam splitter (222) to form the third and fourth laser beams; The third laser beam is frequency-shifted by the acousto-optic modulator (230) to form the pump laser; The fourth laser beam is used to generate the detection laser.

9. The laser-pumped cesium beam tube according to claim 8, characterized in that, The laser optical path system (200) further includes: an isolator (240), a first half-wave plate (251), a second half-wave plate (252), a first beam expander (261), a second beam expander (262), and a third beam expander (263). The original laser emitted by the laser (210) is adjusted sequentially by the isolator (240) and the first half-wave plate (251), and then split by the first polarizing beam splitter (221); After the first laser beam is adjusted by the first beam expander (261), it forms the frequency-stabilized laser. The second laser beam, after being adjusted by the second half-wave plate (252), is split by the second polarizing beam splitter (222); The third laser beam is sequentially adjusted by the acousto-optic modulator (230) and the second beam expander (262) to form the pump laser; The fourth laser beam, after being adjusted by the third beam expander (263), forms the detection laser.

10. The laser-pumped cesium beam tube according to claim 8, characterized in that, The laser optical path system (200) further includes a reflector for adjusting the irradiation direction of the frequency-stabilized laser, the pump laser and the detection laser to be perpendicular to the cesium atom beam.

Images