Rubidium two-photon optical clock system based on single laser excitation and cavity enhancement and processing method

Abstract

The application discloses a kind of based on single laser excitation and cavity enhancement's rubidium two-photon optical clock system and processing method, the device includes: light source, stable light path, laser power stabilization loop, rubidium two-photon transition physical module and fluorescence detection servo control module;Stable light path includes first half-wave plate, isolator and first polarization beam splitter;Foundation light path includes electro-optic modulator, second half-wave plate, second polarization beam splitter, first high reflectivity mirror and first mirror;Frequency reference sub light path includes optical frequency comb, third plano-convex lens, periodically poled lithium niobate crystal, second plano-convex lens and second mirror;Laser power stabilization loop includes piezoelectric ceramic, first photodetector and power stabilization module;Rubidium two-photon transition physical module includes heatable rubidium atom cell, second high reflectivity mirror and magnetic shield cover.The application solves the problems of existing technology, such as complex laser supporting system, large volume and power consumption.

Description

Technical Field

[0001] This invention relates to the field of optical frequency standard technology, specifically to a rubidium two-photon optical clock system and processing method based on single laser excitation and cavity enhancement. Background Technology

[0002] Optical atomic clocks, with their ultra-high precision and frequency stability, have become a core technology in the field of time and frequency metrology. They have demonstrated irreplaceable application potential in many fields, such as verifying fundamental physical laws, high-precision time synchronization in wide-area networks, satellite navigation and positioning, geodesy and gravity detection, driving technological innovation and development in related fields. Among them, alkali metal atomic optical atomic clocks with rubidium atoms as their core are recognized as an important research and development direction for the next generation of portable and mobile atomic frequency standards due to their relatively simple structure and ease of miniaturization and integration design. The 5S1 / 2→5D5 / 2 two-photon transition scheme of rubidium-87 atoms has become the mainstream research direction for rubidium atomic optical clocks due to its unique advantages. This transition corresponds to a wavelength near 778nm, belongs to a dipole forbidden transition, and has an extremely narrow natural linewidth. Theoretically, it can achieve extremely high frequency stability. At the same time, the first-order Doppler effect can be eliminated by opposing propagation laser excitation, reducing the requirements for atomic cooling technology. In addition, rubidium atoms have high vapor pressure, and the implementation scheme based on hot atomic gas cells can eliminate the complex atomic cooling and trapping system, further meeting the application requirements of miniaturization and portability. Therefore, this technical route has received widespread attention and research from the industry.

[0003] Despite the numerous advantages mentioned above, the actual research and development and industrial application of rubidium two-photon optical clocks still face many technical bottlenecks. The core challenge lies in achieving both long-term system stability and miniaturization and low power consumption. In existing technologies, to drive rubidium atoms to achieve effective two-photon transitions and generate a high signal-to-noise ratio detection signal, it is often necessary to increase the power of the incident laser. However, the application of high-power lasers can lead to a series of system errors and technical difficulties: on the one hand, the interaction between the high-power optical field and the rubidium atomic energy levels significantly enhances the AC Stark shift effect, causing a shift in atomic energy levels and directly affecting the frequency accuracy of the optical clock. This shift effect is difficult to compensate for precisely, becoming a key factor limiting the long-term stability of the optical clock. On the other hand, the operation of high-power lasers requires larger power supply modules and complex heat dissipation systems, which not only significantly increases the overall size, weight, and energy consumption of the optical clock but also disrupts the integrated design of the system, contradicting the application requirements of portable and mobile atomic frequency standards. Currently, there is no effective low-power excitation scheme in existing technologies, and it is impossible to ensure the signal strength of two-photon transitions while reducing the incident light power. This makes it difficult for rubidium two-photon optical clocks to simultaneously achieve the technical requirements of high precision, high stability, miniaturization, and low power consumption, which has become a core technical problem that urgently needs to be solved in this field.

[0004] Therefore, there is an urgent need for a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement to solve the problems of complex laser matching systems, large size and power consumption in existing technologies. Summary of the Invention

[0005] To address this, the present invention provides a rubidium two-photon optical clock system and processing method based on single laser excitation and cavity enhancement, which solves the problems of existing rubidium two-photon optical clocks requiring high-power laser excitation for two-photon transitions, which not only induces AC Stark frequency shift, reducing the long-term stability of the system, but also leads to complex laser-related systems, large size and power consumption, making it difficult to achieve both high precision and miniaturization and low power consumption.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement, characterized in that it includes a light source, a stable optical path, a laser power stabilization loop, a rubidium two-photon transition physics module, and a fluorescence detection servo control module; The light source is an external cavity semiconductor laser; the stable optical path includes a first half-wave plate, an isolator, and a first polarizing beam splitter connected in sequence; one optical path of the first polarizing beam splitter is connected to an electro-optic modulator, a second half-wave plate, a second polarizing beam splitter, a first high-reflectivity mirror, and a first mirror; the other optical path of the first polarizing beam splitter is connected to a second mirror; the stable optical path also includes an optical frequency comb, a third plano-convex lens, a periodically polarized lithium niobate crystal, a second plano-convex lens, and a second mirror connected in sequence; The laser power stabilization loop includes a piezoelectric ceramic, a first photodetector, and a power stabilization module; the piezoelectric ceramic is disposed on the rear side of the first reflector; the first photodetector is electrically connected to the piezoelectric ceramic through the power stabilization module. The rubidium two-photon transition physics module includes a heatable rubidium atom gas chamber, a second high-reflectivity mirror, and a magnetic shield. The heatable rubidium atom gas chamber is disposed in the optical path between the first mirror and the second high-reflectivity mirror. The first high-reflectivity mirror and the second high-reflectivity mirror constitute an optical resonant cavity. The magnetic shield covers the outside of the heatable rubidium atom gas chamber. The fluorescence detection servo control module includes a first plano-convex lens, a 420nm filter, a photomultiplier tube, a frequency stabilization servo module, and a second photodetector. The first plano-convex lens, the 420nm filter, and the photomultiplier tube are sequentially arranged above the heatable rubidium atom gas cell. The photomultiplier tube is electrically connected to the external cavity semiconductor laser through the frequency stabilization servo module. The second photodetector is optically connected to the second reflector.

[0007] As a preferred embodiment of a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement, the periodically polarized lithium niobate crystal is used to convert the 1556.2nm fundamental frequency light output from the optical frequency comb into 778.1nm frequency-doubled light; the frequency-doubled light and the vertically polarized laser output from the first polarization beam splitter are combined at the second mirror and then transmitted to the second photodetector.

[0008] As a preferred embodiment of a rubidium two-photon optical clock system based on single-laser excitation and cavity enhancement, both the first half-wave plate and the second half-wave plate are used to adjust the laser polarization state; the isolator is a unidirectional light transmission structure used to prevent reflected light from returning along the original path and damaging the external cavity semiconductor laser; the first polarization beam splitter is used to split the laser into the vertically polarized laser and the horizontally polarized laser; the vertically polarized laser is transmitted to the second reflector; the horizontally polarized laser is transmitted to the electro-optic modulator for phase modulation; the modulated laser sequentially passes through the second half-wave plate, the second polarization beam splitter, the first high-reflectivity reflector, and the first reflector before entering the rubidium two-photon transition physics module.

[0009] As a preferred embodiment of a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement, the first plano-convex lens, the second plano-convex lens, and the third plano-convex lens are all used for beam shaping, controlling the beam divergence angle and spot size, and ensuring that the spot size and waist position are adapted to the requirements of the heatable rubidium atomic gas cell or optical resonator.

[0010] As a preferred embodiment of a rubidium two-photon optical clock system based on single-laser excitation and cavity enhancement, the first plano-convex lens focuses the 420nm blue fluorescence generated by the heatable rubidium atom gas cell; the 420nm filter filters stray light from the focused fluorescence to generate a filtered fluorescence signal; the photomultiplier tube converts the filtered fluorescence signal into an amplified electrical signal and transmits it to the frequency stabilization servo module; the frequency stabilization servo module generates a frequency feedback control signal from the electrical signal after signal processing such as lock-in amplification and transmits it to the external cavity semiconductor laser; the external cavity semiconductor laser adjusts the laser emission frequency according to the frequency feedback control signal.

[0011] As a preferred embodiment of a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement, the magnetic shield is a multi-layer magnetic shielding structure used to shield external magnetic field interference and reduce the influence of the Zeeman effect on the two-photon transition frequency of rubidium atoms; the heatable rubidium atom gas chamber is filled with rubidium 87 atomic vapor to provide the working medium for the two-photon transition of rubidium atoms.

[0012] As a preferred embodiment of a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement, the power stabilization module receives the power detection electrical signal transmitted by the first photodetector, generates and outputs a power feedback control signal to the piezoelectric ceramic after signal processing; the piezoelectric ceramic finely adjusts the position or angle of the optical element according to the power feedback control signal to achieve closed-loop control of the laser power.

[0013] This invention also provides a rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement, including: An external cavity semiconductor laser emits laser light; after the laser's polarization direction is adjusted and unidirectional transmission is controlled sequentially by a first half-wave plate and an isolator, the light is transmitted to a first polarization beam splitter. The laser beam is split into a horizontally polarized laser beam and a vertically polarized laser beam by the first polarization beam splitter, and then transmitted to the electro-optic modulator and the second mirror, respectively. The horizontally polarized laser beam is phase-modulated by the electro-optic modulator to generate an adjusted laser; the adjusted laser is then connected to the rubidium two-photon transition physics module by passing it sequentially through a second half-wave plate, a second polarization beam splitter, a high-reflectivity mirror and a first mirror. The adjusted laser, after passing through the heatable rubidium atom gas chamber, is reversed via a second high-reflectivity mirror; the adjusted laser is enhanced by an optical resonant cavity formed by the first and second high-reflectivity mirrors to generate an enhanced laser; the enhanced laser interacts continuously with the rubidium 87 atoms in the heatable rubidium atom gas chamber, completing a 5S1 / 2 to 5D5 / 2 two-photon transition and generating 420nm blue fluorescence; The blue fluorescence is focused by a first plano-convex lens to form focused fluorescence; stray light is filtered from the focused fluorescence by a 420nm filter to obtain filtered fluorescence; the filtered fluorescence is converted into an amplified electrical signal by a photomultiplier tube and transmitted to a frequency stabilization servo module; the frequency stabilization servo module performs phase-locked amplification on the electrical signal to generate a frequency feedback control signal and transmits it to the external cavity semiconductor laser; the external cavity semiconductor laser is adjusted according to the frequency feedback control signal to adjust the laser emission frequency, thereby locking the laser frequency with the two-photon transition frequency of rubidium-87 atoms.

[0014] As a preferred embodiment of the rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement, the laser power transmitted to the second high-reflectivity mirror is detected by a first photodetector and converted into a power electrical signal, which is then transmitted to a power stabilization module. The power stabilization module generates a power feedback control signal based on the power electrical signal and transmits it to a piezoelectric ceramic. The piezoelectric ceramic fine-tunes the position of the optical element based on the power feedback control signal, thereby controlling the laser power.

[0015] As a preferred embodiment of the rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement, an optical frequency comb emits a 1556.2nm fundamental frequency light; the fundamental frequency light is focused by a third plano-convex lens and transmitted to a periodically polarized lithium niobate crystal; the periodically polarized lithium niobate crystal performs frequency doubling on the focused fundamental frequency light to generate 778.1nm frequency-doubled light; the frequency-doubled light is collimated by a second plano-convex lens and transmitted to a second reflector; the frequency-doubled light is combined with the vertically polarized laser transmitted to the second reflector to generate a combined laser beam, which is then transmitted to a second photodetector; the second photodetector detects the optical power of the combined laser beam and converts it into an electrical signal, thereby achieving calibration and evaluation of the laser frequency.

[0016] The present invention has the following advantages: First, cavity enhancement technology is used to significantly increase the interaction intensity between the laser and rubidium atoms, enabling effective two-photon transitions of rubidium atoms at low incident light power, reducing the average light field intensity on the atoms, decreasing the AC Stark frequency shift, and improving the long-term stability of the system.

[0017] Secondly, the low incident light power requirement reduces the power output requirements of the laser, resulting in less waste heat generated by the laser. This eliminates the need for complex heat dissipation and power supply systems, which helps to achieve system miniaturization and integration, while also reducing overall power consumption.

[0018] Third, the single-laser excitation design simplifies the optical path structure of the system, reduces the use of optical components, and makes the overall layout of the system simpler, easier to build, debug and maintain.

[0019] Fourth, a laser power stabilization loop and a fluorescence detection servo control module are set up to form a dual closed-loop feedback control of power and frequency, which can adjust the laser power and frequency in real time, further improving the stability of system operation.

[0020] Fifth, it is equipped with a magnetic shield and a special filter to effectively shield the interference of external magnetic fields on the rubidium atom energy level, filter stray light in the fluorescence detection process, reduce the influence of external factors on the system, and improve the effectiveness of signal detection.

[0021] Sixth, it eliminates the need for complex atom cooling and trapping systems, enabling two-photon transitions of rubidium atoms solely through a thermal atom gas chamber, further simplifying the system structure and meeting the research and application needs of portable atomic frequency standards. Attached Figure Description

[0022] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0023] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0024] Figure 1 This is a schematic diagram of the architecture of the rubidium two-photon optical clock system based on single laser excitation and cavity enhancement provided in Embodiment 1 of the present invention; Figure 2 This is a flowchart illustrating the rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement provided in Embodiment 2 of the present invention. In the diagram, 1. Magnetic shield; 2. Photomultiplier tube; 3. 420nm filter; 4. First plano-convex lens; 5. First reflector; 6. Piezoelectric ceramic; 7. First high-reflectivity reflector; 8. Heated rubidium atom gas cell; 9. Second high-reflectivity reflector; 10. First photodetector; 11. External cavity semiconductor laser; 12. First half-wave plate; 13. Isolator; 14. First polarization beam splitter; 15. Electro-optic modulator; 16. Second half-wave plate; 17. Second polarization beam splitter; 18. Second photodetector; 19. Second reflector; 20. Second plano-convex lens; 21. Periodically polarized lithium niobate crystal; 22. Third plano-convex lens; 23. Optical frequency comb; 24. Power stabilization module; 25. Frequency stabilization servo module. Detailed Implementation

[0025] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] See Figure 1Embodiment 1 of the present invention provides a rubidium two-photon optical clock system based on single laser excitation and cavity enhancement, including a light source, a stable optical path, a laser power stabilization loop, a rubidium two-photon transition physics module, and a fluorescence detection servo control module; The light source is an external cavity semiconductor laser 11; the stable optical path includes a first half-wave plate 12, an isolator 13, and a first polarization beam splitter 14 connected in sequence; one optical path of the first polarization beam splitter 14 is connected to an electro-optic modulator 15, a second half-wave plate 16, a second polarization beam splitter 17, a first high-reflectivity mirror 7, and a first mirror 5; another optical path of the first polarization beam splitter 14 is connected to a second mirror 19; the stable optical path also includes an optical frequency comb 23, a third plano-convex lens 22, a periodically polarized lithium niobate crystal 21, a second plano-convex lens 20, and a second mirror 19 connected in sequence; Specifically, the light source is an external cavity semiconductor laser 11, which serves as the sole laser excitation source for the entire optical clock system. It is the basis for the optical signals of all optical path components, directly serving as the optical input end of the stable optical path, and providing a 778.1nm laser beam for all subsequent optical path transmission and optical-atomic interaction components of the system. The stable optical path includes a basic optical path control section and a frequency reference sub-optical path section.

[0028] The basic optical path control section consists of a first half-wave plate 12, an isolator 13, and a first polarization beam splitter 14 connected sequentially along the laser transmission direction. This unit is positioned adjacent to the laser output end of the external cavity semiconductor laser 11 and serves as the first optical path control unit for the laser output from the light source. The first polarization beam splitter 14, as the core beam splitting element, divides the laser into two optical paths: a horizontally polarized laser beam and a vertically polarized laser beam. The horizontally polarized laser beam is the main excitation path, sequentially connected to an electro-optic modulator 15, a second half-wave plate 16, a second polarization beam splitter 17, a first high-reflectivity mirror 7, and a first mirror 5. This path element is linearly arranged along the laser transmission direction, with its end directly connected to the optical input end of the rubidium two-photon transition physics module. The vertically polarized laser beam serves as the frequency calibration optical path, directly connected to the second mirror 19, preparing for subsequent frequency calibration laser beam combining.

[0029] The frequency reference sub-optical path section consists of an optical frequency comb 23, a third plano-convex lens 22, a periodically polarized lithium niobate crystal 21, and a second plano-convex lens 20 connected sequentially along the light transmission direction. This serves as the high-precision frequency reference light generation unit of the system. Its end is also connected to the second reflector 19 via an optical path. The optical path of the aforementioned vertically polarized laser beam intersects with that of the second reflector 19, enabling the two laser beams to be combined at the reflector. The second reflector 19 also serves as the output end of the combined beam, which is connected to the optical path of the second photodetector 18 of the fluorescence detection servo control module.

[0030] In this embodiment, the laser power stabilization loop includes a piezoelectric ceramic 6, a first photodetector 10, and a power stabilization module 24; the piezoelectric ceramic 6 is disposed on the rear side of the first reflector 5; the first photodetector 10 is electrically connected to the piezoelectric ceramic 6 through the power stabilization module 24; Specifically, the laser power stabilization loop is the system's closed-loop power control unit, consisting of a piezoelectric ceramic 6, a first photodetector 10, and a power stabilization module 24. It is a key component for ensuring stable laser power and preventing power fluctuations from affecting light-atom interactions. Each component is set according to the electrical signal feedback logic of detection-processing-execution: the piezoelectric ceramic 6 is set close to the rear side of the first reflector 5, forming a mechanical linkage structure with the first reflector 5, and can adjust the position or angle of the first reflector 5 through its own micro-displacement; the first photodetector 10 is set at the end of the laser reverse transmission optical path of the rubidium two-photon transition physics module, facing the laser output direction of the second high-reflectivity reflector 9, and can detect the laser power after reverse transmission in real time; the power stabilization module 24, as the core of the electrical control, establishes bidirectional electrical connections with the first photodetector 10 and the piezoelectric ceramic 6 respectively, forming a complete electrical signal transmission and feedback link.

[0031] In this embodiment, the rubidium two-photon transition physics module includes a heatable rubidium atom gas cell 8, a second high-reflectivity mirror 9, and a magnetic shield 1; the heatable rubidium atom gas cell 8 is disposed in the optical path between the first mirror 7 and the second high-reflectivity mirror 9; the first high-reflectivity mirror 7 and the second high-reflectivity mirror 9 constitute an optical resonant cavity; the magnetic shield 1 covers the outside of the heatable rubidium atom gas cell 8; Specifically, the rubidium two-photon transition physics module is the core physical unit for realizing the two-photon transition of rubidium-87 atoms in the system. It consists of a heatable rubidium atom gas cell 8, a second high-reflectivity mirror 9, and a magnetic shield 1. The components are arranged with the heatable rubidium atom gas cell 8 as the core: the heatable rubidium atom gas cell 8, as the core carrier of light-atom interaction, is set in the straight optical path between the first mirror 5 and the second high-reflectivity mirror 9, and is the core action area of ​​the laser after the stable optical path modulation; the first high-reflectivity mirror 7 and the second high-reflectivity mirror 9 are set opposite to each other, forming an optical resonant cavity with the heatable rubidium atom gas cell 8 as the center, so that the laser will form multiple reflections in the gas cell region; the magnetic shield 1 is set outside the heatable rubidium atom gas cell 8 in a fully enclosed manner, completely enclosing the gas cell and isolating the influence of the external magnetic field on the rubidium atoms inside the gas cell.

[0032] In this embodiment, the fluorescence detection servo control module includes a first plano-convex lens 4, a 420nm filter 3, a photomultiplier tube 2, a frequency stabilization servo module 25, and a second photodetector 18. The first plano-convex lens 4, the 420nm filter 3, and the photomultiplier tube 2 are sequentially arranged above the heatable rubidium atom gas chamber 8. The photomultiplier tube 2 is electrically connected to the external cavity semiconductor laser 11 through the frequency stabilization servo module 25. The second photodetector 18 is optically connected to the second reflector 19.

[0033] Specifically, the fluorescence detection servo control module is the system's fluorescence detection, frequency closed-loop control, and frequency calibration unit. It consists of a first plano-convex lens 4, a 420nm filter 3, a photomultiplier tube 2, a frequency stabilization servo module 25, and a second photodetector 18. Each component is arranged according to two functional branches: fluorescence detection and frequency calibration. They are respectively connected to the rubidium two-photon transition physics module and the beam combining optical path of the stabilizing optical path. The first plano-convex lens 4, the 420nm filter 3, and the photomultiplier tube 2 are arranged in the order of fluorescence reception above the heatable rubidium atom gas cell 8 to form a dedicated optical path for fluorescence detection. The photomultiplier tube 2 is electrically connected to the frequency stabilization servo module 25, which is then electrically connected to the external cavity semiconductor laser 11 to form a frequency closed-loop electrical control link from fluorescence detection to laser frequency adjustment. The second photodetector 18 is located at the end of the beam combining optical path, facing the beam combining laser output direction of the second reflector 19, and directly receives the combined laser signal.

[0034] In this embodiment, the periodically polarized lithium niobate crystal 21 is used to convert the 1556.2nm fundamental frequency light output by the optical frequency comb 23 into 778.1nm frequency-doubled light; the frequency-doubled light and the vertically polarized laser output by the first polarization beam splitter 14 are combined at the second reflector 19 and then transmitted to the second photodetector 18.

[0035] Specifically, the 1556.2nm fundamental frequency light output from the optical frequency comb 23 is focused by the third plano-convex lens 22 and then incident on the periodically polarized lithium niobate crystal 21 with a suitable spot size and intensity. This crystal, through a nonlinear optical frequency doubling effect, precisely converts the 1556.2nm infrared fundamental frequency light into a 778.1nm frequency-doubled light. This frequency-doubled light inherits the high-precision frequency stability of the optical frequency comb 23, becoming a high-precision frequency reference laser that can be directly compared with the system's working laser. The converted 778.1nm frequency-doubled light is then collimated by the second plano-convex lens 20 to ensure the beam's propagation direction and quality, and then directionally transmitted to the second reflector 19, preparing for subsequent optical path beam combining.

[0036] In this embodiment, both the first half-wave plate 12 and the second half-wave plate 16 are used to adjust the laser polarization state; the isolator 13 is a unidirectional light transmission structure used to prevent reflected light from returning along the original path and damaging the external cavity semiconductor laser 11; the first polarization beam splitter 14 is used to split the laser into the vertically polarized laser and the horizontally polarized laser; the vertically polarized laser is transmitted to the second reflector 19; the horizontally polarized laser is transmitted to the electro-optic modulator 15 for phase modulation; the modulated laser passes sequentially through the second half-wave plate 16, the second polarization beam splitter 17, the first high-reflectivity reflector 7, and the first reflector 5 before entering the rubidium two-photon transition physics module.

[0037] Specifically, the first half-wave plate 12, serving as a pre-calibration element for the laser polarization state, is connected in series in the optical path between the external cavity semiconductor laser 11 and the isolator 13. Its core function is not merely to adjust the laser polarization state, but to adjust the original laser polarization state output from the laser 11 to a working polarization state suitable for subsequent polarization-sensitive optical elements such as the isolator 13 and the first polarization beam splitter 14. The second half-wave plate 16, positioned between the electro-optic modulator 15 and the second polarization beam splitter 17, is a fine-tuning element for the polarization state of the modulated laser, forming a "preliminary adjustment + fine-tuning" polarization control combination with the first half-wave plate 12. After the laser undergoes phase modulation by the electro-optic modulator 15, its polarization state undergoes a slight shift. The second half-wave plate 16 precisely fine-tunes this shift, restoring the laser polarization state to its optimal state suitable for the operation of subsequent elements, ensuring the laser transmission efficiency of the main excitation optical path and the effectiveness of subsequent cavity enhancement and light-atom interaction.

[0038] Isolator 13 is a unidirectional light transmission structure with high reverse light suppression capability. It is located between the first half-wave plate 12 and the first polarizing beam splitter 14 and acts as a "one-way valve" for ensuring the stable operation of the light source. Isolator 13 only allows laser light to propagate in the forward direction of "laser 11 → first polarizing beam splitter 14", effectively blocking the reverse return light. It isolates the interference of reverse light on the light source at the optical path level, which not only ensures the stability of the laser output, but also extends the service life of the light source.

[0039] The first polarization beam splitter 14 is the core component in the stable optical path that realizes the functional splitting of the laser. It receives the laser after initial polarization modulation and unidirectional transmission. Based on the polarization characteristics of the laser, it accurately separates the single laser beam into two laser beams with mutually perpendicular polarization directions: a vertically polarized laser and a horizontally polarized laser. At the same time, it can realize the rational allocation of optical power according to the system's working requirements: to ensure the light-atom interaction effect of the main excitation optical path, most of the optical power is allocated to the horizontally polarized laser (main excitation optical path), and a small portion of the optical power is allocated to the vertically polarized laser (frequency calibration sampling optical path). The vertically polarized laser, as the sampling light of the system's working laser, is directly and directionally transmitted to the second reflector 19 to provide a laser source for the subsequent frequency calibration optical path; the horizontally polarized laser, as the main laser for exciting the two-photon transition of rubidium atoms, is directionally transmitted to the electro-optic modulator 15 for phase modulation, completing the functional optical path allocation of the laser.

[0040] The electro-optic modulator 15 is specifically designed for the horizontally polarized master laser and serves as the laser phase control element in the main excitation optical path. Through phase modulation, the laser forms a specific phase modulation signal, providing a phase reference for the subsequent fluorescence detection servo control module to extract the frequency error signal and achieve precise laser frequency locking. This ensures the feasibility of subsequent frequency closed-loop control. The modulated horizontally polarized laser will then enter the subsequent polarization fine-tuning and optical path selection stages.

[0041] The second polarization beam splitter 17 plays a role in filtering out stray polarized light and purifying the optical path in the main excitation optical path. It performs secondary polarization screening on the laser after polarization fine-tuning, allowing only lasers that conform to the preset polarization direction to pass through, filtering out stray polarized light generated during phase modulation and polarization fine-tuning, and ensuring that the laser polarization state entering the subsequent reflector and rubidium two-photon transition physics module is single and stable.

[0042] The first high-reflectivity mirror 7 and the first mirror 5 are connected in series in the optical path transmission sequence between the second polarization beam splitter 17 and the rubidium two-photon transition physics module. They serve as precise optical path deflection elements for the main excitation optical path. Working together, they directionally deflect the horizontally polarized laser, which has undergone multiple modulations and purification, according to the system's preset optical path direction. This ensures that the laser, with a precise incident angle and propagation direction, successfully enters the optical input end of the rubidium two-photon transition physics module, guaranteeing that the laser accurately enters the core working region of the heatable rubidium atom gas cell 8. Simultaneously, the first high-reflectivity mirror 7 also serves as a component of the subsequent optical resonant cavity, providing a foundation for laser cavity enhancement effects and achieving seamless integration between the optical path deflection and subsequent core components.

[0043] In this embodiment, the first plano-convex lens 4, the second plano-convex lens 20 and the third plano-convex lens 22 are all used for beam shaping, controlling the beam divergence angle and the size of the light spot, and ensuring that the size of the light spot and the waist position are adapted to the requirements of the heatable rubidium atom gas cell 8 or the optical resonant cavity.

[0044] Specifically, the core functions of the first plano-convex lens 4, the second plano-convex lens 20, and the third plano-convex lens 22 are all beam shaping, which can control the beam divergence angle and the size of the beam spot, ensuring that the size of the beam spot and the waist position are adapted to the working requirements of the heatable rubidium atom gas cell 8 or the optical resonator.

[0045] Among them, the first plano-convex lens 4 is adapted to the beam shaping requirements of the fluorescence detection optical path; the second plano-convex lens 20 and the third plano-convex lens 22 are adapted to the beam shaping requirements of the frequency reference sub-optical path. Through targeted beam control, the three lenses ensure the light transmission and light interaction efficiency of the corresponding optical paths, while indirectly adapting to the working requirements of the optical resonator, thus helping the system to operate stably.

[0046] In this embodiment, the first plano-convex lens 4 focuses the 420nm blue fluorescence generated by the heatable rubidium atom gas cell 8; the 420nm filter 3 filters the stray light from the focused fluorescence to generate a filtered fluorescence signal; the photomultiplier tube 2 converts the filtered fluorescence signal into an amplified electrical signal and transmits it to the frequency stabilization servo module 25; the frequency stabilization servo module 25 generates a frequency feedback control signal after the electrical signal undergoes signal processing such as lock-in amplification and transmits it to the external cavity semiconductor laser 11; the external cavity semiconductor laser 11 adjusts the laser emission frequency according to the frequency feedback control signal.

[0047] Specifically, after a two-photon transition, the heatable rubidium atom gas cell 8 emits 420nm blue fluorescence. This fluorescence is spatially focused by the first plano-convex lens 4 to reduce signal loss caused by fluorescence divergence. It then passes through a 420nm filter 3 to remove ambient stray light and non-target wavelength interference, resulting in a pure filtered fluorescence signal. This fluorescence signal is converted from optical to electrical signal by a photomultiplier tube 2 and amplified. The amplified electrical signal is then transmitted to the frequency stabilization servo module 25. The frequency stabilization servo module 25 performs a series of signal processing operations, including phase-locked amplification, to extract frequency error information and generate a corresponding frequency feedback control signal, which is then transmitted in real-time to the external cavity semiconductor laser 11. The external cavity semiconductor laser 11 adjusts its laser emission frequency according to the received frequency feedback control signal, thereby achieving dynamic control of the output laser frequency.

[0048] In this embodiment, the magnetic shielding cover 1 is a multi-layer magnetic shielding structure used to shield external magnetic field interference and reduce the influence of the Zeeman effect on the two-photon transition frequency of rubidium atoms; the heatable rubidium atom gas chamber 8 is filled with rubidium 87 atomic vapor to provide the working medium for the two-photon transition of rubidium atoms.

[0049] Specifically, the magnetic shield 1 adopts a multi-layer magnetic shielding structure design, which can effectively block stray magnetic fields in the external environment from interfering with the internal working area, and avoid the splitting and shifting of rubidium atom energy levels caused by the Zeeman effect induced by the external magnetic field. This reduces the adverse effect of the Zeeman effect on the two-photon transition frequency of rubidium atoms and provides a stable magnetic field environment for the two-photon transition process. The heatable rubidium atom gas chamber 8 is filled with rubidium 87 atomic vapor. By heating and regulating, a suitable atomic vapor density can be maintained inside, providing a stable and sufficient interaction medium for the interaction between laser and atoms and the two-photon transition process of rubidium atoms from 5S1 / 2 to 5D5 / 2, ensuring that the two-photon transition can occur stably and efficiently.

[0050] In this embodiment, the power stabilization module 24 receives the power detection electrical signal transmitted by the first photodetector 10, generates and outputs a power feedback control signal to the piezoelectric ceramic 6 after signal processing; the piezoelectric ceramic 6 finely adjusts the position or angle of the optical element according to the power feedback control signal to realize closed-loop control of laser power.

[0051] Specifically, the first photodetector 10 detects the laser power output by the second high-reflectivity mirror 9 in real time, accurately converting the optical signal into a corresponding electrical signal. This electrical signal carries the real-time status information of the laser power in the main excitation optical path and is then continuously transmitted to the power stabilization module 24. After receiving the power detection electrical signal, the power stabilization module 24 performs filtering, amplification, and demodulation to remove environmental interference noise, extract the true fluctuation information of the laser power, and compares it with the system's preset optimal laser power threshold to determine if there is a deviation in the current laser power and the magnitude of that deviation. Based on the comparison results, the power stabilization module 24 generates and outputs a power feedback control signal adapted to the working characteristics of the piezoelectric ceramic 6. The intensity and phase of this signal correspond to the degree of laser power deviation, ensuring the accuracy of the control. The piezoelectric ceramic 6 is tightly attached to the rear side of the first mirror 5, forming a mechanical linkage structure with the first mirror 5. After receiving the power feedback control signal, it will generate a small extension or retraction displacement according to the signal command, thereby driving the position or angle of the first mirror 5 to be accurately fine-tuned. This fine-tuning changes the propagation direction and coupling efficiency of the laser in the main excitation optical path, thereby dynamically adjusting the laser power entering the rubidium two-photon transition physics module, so that the laser power is always stable within the preset optimal range.

[0052] In summary, the operating principle of this invention is as follows: An external cavity semiconductor laser 11 emits 778.1nm laser light, which is then polarized by a first half-wave plate 12 and transmitted unidirectionally by an isolator 13. It is then split into a horizontally polarized laser and a vertically polarized laser by a first polarization beam splitter 14. The horizontally polarized laser is phase-modulated by an electro-optic modulator 15, re-polarized by a second half-wave plate 16, and filtered by a second polarization beam splitter 17. It then passes through a first high-reflectivity mirror 7 and a first mirror 5 and enters the rubidium two-photon transition physics module, forming a cavity increase within the optical resonant cavity formed by the first high-reflectivity mirror 7 and the second high-reflectivity mirror 9. A high-power laser interacts with rubidium 87 atomic vapor in a heatable rubidium atomic chamber 8, causing a 5S1 / 2 to 5D5 / 2 two-photon transition and generating 420nm blue fluorescence. A magnetic shield 1 shields the external magnetic field throughout the process to reduce Zeeman effect interference. The fluorescence is focused by a first plano-convex lens 4, and stray light is filtered out by a 420nm filter 3. The fluorescence is then converted into an amplified electrical signal by a photomultiplier tube 2 and transmitted to a frequency stabilization servo module 25. The module generates a frequency feedback control signal through lock-in amplification and transmits it back to the external cavity semiconductor laser 11, achieving closed-loop locking between the laser frequency and the atomic transition frequency. At the same time, the first photodetector 10 collects the laser power signal in real time and transmits it to the power stabilization module 24. The module generates a power feedback control signal to drive the piezoelectric ceramic 6 to fine-tune the position or angle of the first reflector 5, thereby completing the closed-loop control of the laser power. In addition, the 1556.2nm fundamental frequency light output by the optical frequency comb 23 is focused by the third plano-convex lens 22, frequency-doubled to 778.1nm by the periodically polarized lithium niobate crystal 21, collimated by the second plano-convex lens 20, and then combined with the vertically polarized laser at the second reflector 19. Finally, the second photodetector 18 completes the detection, realizing the calibration reference of the system's laser frequency. The entire system achieves stable and reliable operation of the rubidium two-photon optical clock through the coordinated work of optical path transmission, cavity enhancement, and dual closed-loop feedback.

[0053] Example 2

[0054] See Figure 2 Embodiment 2 of the present invention also provides a rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement, including: S1. An external cavity semiconductor laser emits laser light; after the laser's polarization direction is adjusted and unidirectional transmission is controlled sequentially through a first half-wave plate and an isolator, the light is transmitted to a first polarization beam splitter. S2. The laser beam is split into a horizontally polarized laser beam and a vertically polarized laser beam by the first polarization beam splitter, and then transmitted to the electro-optic modulator and the second reflector, respectively. S3. The horizontally polarized laser beam is phase-modulated by the electro-optic modulator to generate an adjusted laser; the adjusted laser is then connected to the rubidium two-photon transition physics module by passing it sequentially through a second half-wave plate, a second polarization beam splitter, a high-reflectivity mirror and a first mirror. S4. The adjusted laser, after passing through the heatable rubidium atom gas chamber, is reversed and transmitted through a second high-reflectivity mirror; the adjusted laser is enhanced by an optical resonant cavity formed by the first and second high-reflectivity mirrors to generate an enhanced laser; the enhanced laser interacts continuously with the rubidium 87 atoms in the heatable rubidium atom gas chamber to complete the 5S1 / 2 to 5D5 / 2 two-photon transition and generate 420nm blue fluorescence; S5. The blue fluorescence is focused by a first plano-convex lens to form focused fluorescence; stray light is filtered from the focused fluorescence by a 420nm filter to obtain filtered fluorescence; the filtered fluorescence is converted into an amplified electrical signal by a photomultiplier tube and transmitted to a frequency stabilization servo module; the frequency stabilization servo module performs phase-locked amplification on the electrical signal to generate a frequency feedback control signal and transmits it to the external cavity semiconductor laser; the external cavity semiconductor laser is adjusted according to the frequency feedback control signal to adjust the laser emission frequency, thereby locking the laser frequency with the two-photon transition frequency of rubidium-87 atoms.

[0055] In this embodiment, in step S1, the external cavity semiconductor laser emits laser light; after the polarization direction of the laser light is adjusted and unidirectional transmission is controlled by the first half-wave plate and the isolator, the laser light is transmitted to the first polarization beam splitter.

[0056] Specifically, the external cavity semiconductor laser serves as the system's sole laser output source, emitting a 778.1nm laser with a wavelength matching the two-photon transition of rubidium-87 atoms, providing the fundamental excitation source for subsequent atomic interactions. The first half-wave plate adjusts the polarization state of the original laser output to a state suitable for the operation of subsequent optical components, ensuring optical path transmission efficiency. The isolator constructs a unidirectional optical transmission path, blocking reflected light generated by subsequent optical paths from returning along the original path, preventing reflected light from interfering with the operational stability of the external cavity semiconductor laser or even causing device damage. The laser, after polarization adjustment and unidirectional protection, is stably transmitted to the first polarization beam splitter, preparing for subsequent optical path beam splitting.

[0057] In this embodiment, in step S2, the laser is split into a horizontally polarized laser beam and a vertically polarized laser beam by the first polarization beam splitter, and then transmitted to the electro-optic modulator and the second reflector, respectively.

[0058] Specifically, relying on the polarization splitting characteristics of the first polarization beam splitter, a single laser beam is split into two beams with different functions according to the polarization direction. The horizontally polarized laser beam serves as the main optical path laser for exciting the two-photon transition of rubidium atoms and is transmitted to the electro-optic modulator for phase modulation processing. The vertically polarized laser beam serves as the sampling laser for system frequency calibration and is directionally transmitted to the second reflector to prepare for subsequent beam combining calibration. The polarization directions of the two lasers are perpendicular to each other, so they will not interfere with each other during transmission. At the same time, the optical power can be reasonably distributed to ensure that the main excitation optical path has sufficient optical power to support the two-photon transition.

[0059] In this embodiment, in step S3, the horizontally polarized laser beam is phase-modulated by the electro-optic modulator to generate an adjusted laser; the adjusted laser is then connected to the rubidium two-photon transition physics module by passing it sequentially through a second half-wave plate, a second polarization beam splitter, a high-reflectivity mirror, and a first mirror.

[0060] Specifically, the electro-optic modulator applies a phase modulation signal to the horizontally polarized laser beam, providing identification features for the subsequent frequency stabilization servo module to extract frequency error signals and generate an adjusted laser that meets the closed-loop control requirements; the second half-wave plate performs fine-tuning on the polarization state of the modulated laser, correcting the polarization shift caused by phase modulation; the second polarization beam splitter filters out stray polarization components in the optical path to ensure the purity of laser polarization; the first high-reflectivity mirror and the first reflector sequentially deflect the laser's optical path, enabling the adjusted laser to precisely enter the rubidium two-photon transition physics module at a matched incident angle, ensuring that the laser can smoothly enter the core operating region.

[0061] In this embodiment, in step S4, the adjusted laser after passing through the heatable rubidium atom gas chamber is reversed through the second high-reflectivity mirror; the adjusted laser is enhanced by the optical resonant cavity formed by the first and second high-reflectivity mirrors to generate enhanced laser; the enhanced laser interacts continuously with the rubidium 87 atoms in the heatable rubidium atom gas chamber to complete the 5S1 / 2 to 5D5 / 2 two-photon transition and generate 420nm blue fluorescence.

[0062] Specifically, after the adjusted laser passes through the heatable rubidium atom gas chamber, the light path is refracted and transmitted in the opposite direction by the second high-reflectivity mirror. Multiple round-trip reflections are formed in the optical resonant cavity formed by the first and second high-reflectivity mirrors. The cavity enhancement effect greatly improves the local light field intensity, and an enhanced laser that meets the transition requirements can be formed at a low incident power. The enhanced laser interacts fully with the rubidium 87 atomic vapor in the heatable rubidium atom gas chamber, exciting the rubidium atoms to complete the 5S1 / 2 to 5D5 / 2 two-photon transition. During the atomic energy level transition, a characteristic 420nm blue fluorescence is emitted, providing the original signal source for subsequent frequency detection. At the same time, the magnetic shielding structure can shield the external magnetic field, ensuring that the transition process is not affected by the Zeeman effect.

[0063] In this embodiment, in step S5, the blue fluorescence is focused by a first plano-convex lens to form focused fluorescence; stray light is filtered from the focused fluorescence by a 420nm filter to obtain filtered fluorescence; the filtered fluorescence is converted into an amplified electrical signal by a photomultiplier tube and transmitted to a frequency stabilization servo module; the frequency stabilization servo module performs phase-locked amplification on the electrical signal to generate a frequency feedback control signal and transmits it to the external cavity semiconductor laser; the external cavity semiconductor laser is adjusted according to the frequency feedback control signal to adjust the laser emission frequency, thereby locking the laser frequency with the two-photon transition frequency of rubidium-87 atoms.

[0064] Specifically, the first plano-convex lens efficiently focuses the spatially divergent blue fluorescence, reducing fluorescence signal loss and improving collection efficiency; the 420nm filter precisely filters out ambient stray light and interference light from other wavelengths, retaining only the pure 420nm fluorescence signal; the photomultiplier tube converts the weak fluorescence signal into an electrical signal and amplifies it for subsequent signal processing; the frequency stabilization servo module extracts frequency error information through lock-in amplification and generates a corresponding frequency feedback control signal; the external cavity semiconductor laser corrects its own emission frequency in real time based on this feedback signal, ensuring that the laser frequency is always consistent with the two-photon transition frequency from 5S1 / 2 to 5D5 / 2 of rubidium-87 atoms, forming a frequency closed-loop lock and ensuring the stability of the system output frequency.

[0065] In this embodiment, the laser power transmitted to the second high-reflectivity mirror is detected by a first photodetector and converted into a power electrical signal, which is then transmitted to a power stabilization module. The power stabilization module generates a power feedback control signal based on the power electrical signal and transmits it to a piezoelectric ceramic. The piezoelectric ceramic fine-tunes the position of the optical element based on the power feedback control signal, thereby controlling the laser power.

[0066] Specifically, the first photodetector monitors and collects the laser power transmitted to the second high-reflectivity mirror in real time, converts the detected laser power signal into a corresponding power electrical signal, and transmits this electrical signal to the power stabilization module in real time. The power stabilization module performs signal processing such as filtering, amplification, and difference comparison on the received power electrical signal. Based on the deviation between the real-time detected power and the system set power, it generates a corresponding power feedback control signal and sends it to the piezoelectric ceramic. After receiving the power feedback control signal, the piezoelectric ceramic generates controllable micro-stretching deformation according to the electrical signal command, making slight adjustments to the position or angle of the optical element connected to it. This changes the optical path transmission state and coupling efficiency of the laser, thereby dynamically smoothing the fluctuation of laser power and realizing stable closed-loop control of laser power. This ensures that the laser power incident on the rubidium two-photon transition physics module remains stable, providing stable and reliable excitation light field conditions for rubidium atom two-photon transitions.

[0067] In this embodiment, an optical frequency comb emits a 1556.2nm fundamental frequency light; the fundamental frequency light is focused by a third plano-convex lens and transmitted to a periodically polarized lithium niobate crystal; the periodically polarized lithium niobate crystal performs frequency doubling on the focused fundamental frequency light to generate 778.1nm frequency-doubled light; the frequency-doubled light is collimated by a second plano-convex lens and transmitted to a second reflector; the frequency-doubled light is combined with the vertically polarized laser transmitted to the second reflector to generate a combined laser beam, which is then transmitted to a second photodetector; the second photodetector detects the optical power of the combined laser beam and converts it into an electrical signal, thereby achieving calibration and evaluation of the laser frequency.

[0068] Specifically, a stable 1556.2nm fundamental frequency light is emitted outward from the optical frequency comb. This fundamental frequency light serves as the reference light source for the system's laser frequency calibration. It is first focused by a third plano-convex lens to reduce the beam spot size and increase the optical power density, enabling efficient coupling into the periodically polarized lithium niobate crystal. Subsequently, the periodically polarized lithium niobate crystal utilizes its own nonlinear optical frequency doubling effect to perform wavelength frequency doubling on the focused 1556.2nm fundamental frequency light, generating a 778.1nm frequency-doubled light with the same wavelength as the system's main excitation laser, ensuring wavelength matching between the frequency reference light and the working laser. The frequency-doubled light is then passed through a second plano-convex lens... Collimation and shaping compress the beam divergence angle and regulate the beam spot shape, enabling it to propagate stably to the second reflector. Under the optical path action of the second reflector, the frequency-doubled light and the vertically polarized laser transmitted from the first polarization beam splitter are spatially combined to form a combined laser beam carrying both frequency reference information and system operating laser information, which is then directionally transmitted to the second photodetector. The second photodetector detects the optical power and frequency characteristics of the combined laser beam, converting the optical signal into a corresponding electrical signal. By analyzing and comparing the electrical signal, the system laser frequency is calibrated and comprehensively evaluated, providing a reference for improving the frequency stability of the optical clock operation.

[0069] The application scenarios of this invention are as follows: In the context of spaceborne navigation and satellite timing, this invention, with its compact system structure and stable frequency output characteristics, provides a reliable time and frequency reference for satellite platform timing synchronization and orbit positioning calculation, thus meeting the on-orbit operation requirements of lightweight and long-endurance spacecraft.

[0070] In the terrestrial 5G / 6G communication backbone network timing scenario, this invention can provide a stable time reference for communication base stations and optical fiber transmission nodes, ensuring the timing coordination of massive data transmission and base station signal switching, and maintaining the stable operation of the overall communication network.

[0071] In the scenario of wide-area dispatching and operation and maintenance of power grids, this invention can provide a unified time reference for power grid relay protection, fault recording, and wide-area measurement systems, ensuring that the actions of equipment in various areas of the power grid are consistent and improving the overall stability of the power system operation.

[0072] In the context of airborne navigation and airborne telemetry and control, this invention can adapt to complex airborne environmental fluctuations, providing a stable frequency reference for aircraft navigation and positioning, and airborne equipment interaction and control, ensuring the continuity of signal transmission and equipment operation during flight.

[0073] In the context of quantum measurement and atomic physics experiments in fundamental physics, this invention can serve as a frequency reference device for studying atomic energy level characteristics and verifying physical parameters, providing stable and continuous experimental support for related scientific research.

[0074] In the context of frequency standard verification by local metrology institutions, this invention can be used for the comparison and transmission of time and frequency values, to complete the calibration of various timing and frequency measurement devices, and to improve the regional time and frequency metrology system.

[0075] In the scenario of establishing inter-satellite laser communication links, this invention provides a stable frequency reference for laser signal transmission and reception and data encoding transmission, reduces timing deviations in link transmission, and improves the smoothness of inter-satellite data interaction.

[0076] It should be noted that the present invention has been described in a relatively specific and detailed manner above through general descriptions and specific embodiments. It should be understood that, based on the technical concept of the present invention, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not depart from the technical concept of the present invention, the technical solutions obtained by these conventional adjustments or further innovations also fall within the protection scope of the claims of the present invention.

Claims

1. A rubidium two-photon optical clock system based on single-laser excitation and cavity enhancement, characterized in that, It includes a light source, a stable optical path, a laser power stabilization loop, a rubidium two-photon transition physics module, and a fluorescence detection servo control module; The light source is an external cavity semiconductor laser (11); the stable optical path includes a first half-wave plate (12), an isolator (13), and a first polarization beam splitter (14) connected in sequence; one optical path of the first polarization beam splitter (14) is connected to an electro-optic modulator (15), a second half-wave plate (16), a second polarization beam splitter (17), a first high-reflectivity mirror (7), and a first mirror (5); the other optical path of the first polarization beam splitter (14) is connected to a second mirror (19); the stable optical path also includes an optical frequency comb (23), a third plano-convex lens (22), a periodically polarized lithium niobate crystal (21), a second plano-convex lens (20), and a second mirror (19) connected in sequence. The laser power stabilization loop includes a piezoelectric ceramic (6), a first photodetector (10), and a power stabilization module (24); the piezoelectric ceramic (6) is disposed on the rear side of the first reflector (5); the first photodetector (10) is electrically connected to the piezoelectric ceramic (6) through the power stabilization module (24); The rubidium two-photon transition physics module includes a heatable rubidium atom gas chamber (8), a second high-reflectivity mirror (9), and a magnetic shield (1); the heatable rubidium atom gas chamber (8) is disposed in the optical path between the first mirror (5) and the second high-reflectivity mirror (9); the first high-reflectivity mirror (7) and the second high-reflectivity mirror (9) constitute an optical resonant cavity; the magnetic shield (1) covers the outside of the heatable rubidium atom gas chamber (8); The fluorescence detection servo control module includes a first plano-convex lens (4), a 420nm filter (3), a photomultiplier tube (2), a frequency stabilization servo module (25), and a second photodetector (18). The first plano-convex lens (4), the 420nm filter (3), and the photomultiplier tube (2) are arranged in sequence above the heatable rubidium atom gas chamber (8). The photomultiplier tube (2) is electrically connected to the external cavity semiconductor laser (11) through the frequency stabilization servo module (25). The second photodetector (18) is optically connected to the second reflector (19).

2. The rubidium two-photon optical clock system based on single laser excitation and cavity enhancement according to claim 1, characterized in that, The periodically polarized lithium niobate crystal (21) is used to convert the 1556.2nm fundamental frequency light output by the optical frequency comb (23) into 778.1nm frequency-doubled light; the frequency-doubled light and the vertically polarized laser output by the first polarization beam splitter (14) are combined at the second reflector (19) and then transmitted to the second photodetector (18).

3. The rubidium two-photon optical clock system based on single-laser excitation and cavity enhancement according to claim 2, characterized in that, Both the first half-wave plate (12) and the second half-wave plate (16) are used to adjust the laser polarization state; the isolator (13) is a unidirectional light transmission structure used to prevent reflected light from returning along the original path and damaging the external cavity semiconductor laser (11); the first polarization beam splitter (14) is used to split the laser into the vertically polarized laser and the horizontally polarized laser; the vertically polarized laser is transmitted to the second reflector (19); the horizontally polarized laser is transmitted to the electro-optic modulator (15) for phase modulation; the modulated laser passes through the second half-wave plate (16), the second polarization beam splitter (17), the first high reflectivity reflector (7) and the first reflector (5) in sequence, and then enters the rubidium two-photon transition physics module.

4. The rubidium two-photon optical clock system based on single-laser excitation and cavity enhancement according to claim 3, characterized in that, The first plano-convex lens (4), the second plano-convex lens (20) and the third plano-convex lens (22) are all used for beam shaping, controlling the beam divergence angle and the size of the beam spot, and ensuring that the size of the beam spot and the waist position are adapted to the requirements of the heatable rubidium atom gas cell (8) or optical resonator.

5. The rubidium two-photon optical clock system based on single laser excitation and cavity enhancement according to claim 4, characterized in that, The first plano-convex lens (4) focuses the 420nm blue fluorescence generated by the heatable rubidium atom gas cell (8); the 420nm filter (3) filters the stray light of the focused fluorescence to generate a filtered fluorescence signal; the photomultiplier tube (2) converts the filtered fluorescence signal into an amplified electrical signal and transmits it to the frequency stabilization servo module (25); the frequency stabilization servo module (25) generates a frequency feedback control signal after the electrical signal is processed by lock-in amplification and other signal processing, and transmits it to the external cavity semiconductor laser (11); the external cavity semiconductor laser (11) adjusts the laser emission frequency according to the frequency feedback control signal.

6. The rubidium two-photon optical clock system based on single laser excitation and cavity enhancement according to claim 5, characterized in that, The magnetic shield (1) is a multi-layer magnetic shielding structure used to shield external magnetic field interference and reduce the influence of Zeeman effect on the two-photon transition frequency of rubidium atoms; the heatable rubidium atom gas chamber (8) is filled with rubidium 87 atomic vapor to provide the working medium for the two-photon transition of rubidium atoms.

7. The rubidium two-photon optical clock system based on single laser excitation and cavity enhancement according to claim 6, characterized in that, The power stabilization module (24) receives the power detection electrical signal transmitted by the first photodetector (10), generates and outputs a power feedback control signal to the piezoelectric ceramic (6) after signal processing; the piezoelectric ceramic (6) finely adjusts the position or angle of the optical element according to the power feedback control signal to realize closed-loop control of laser power.

8. A rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement, characterized in that, include: An external cavity semiconductor laser (11) emits laser light; after the polarization direction of the laser light is adjusted and unidirectional transmission is controlled by the first half-wave plate (12) and the isolator (13), the laser light is transmitted to the first polarization beam splitter (14). The laser beam is split into a horizontally polarized laser beam and a vertically polarized laser beam by the first polarization beam splitter (14), and then transmitted to the electro-optic modulator (15) and the second mirror (19), respectively. The horizontally polarized laser beam is phase-modulated by the electro-optic modulator (15) to generate an adjusted laser beam; the adjusted laser beam is then connected to the rubidium two-photon transition physics module by passing through the second half-wave plate (16), the second polarization beam splitter (17), a high-reflectivity mirror (7), and the first mirror (5) in sequence. The adjusted laser, after passing through the heatable rubidium atom gas chamber (8), is reversed through the second high-reflectivity mirror (9); the adjusted laser is enhanced by the optical resonant cavity formed by the first high-reflectivity mirror (7) and the second high-reflectivity mirror (9) to generate an enhanced laser; the enhanced laser interacts continuously with the rubidium 87 atoms in the heatable rubidium atom gas chamber (8) to complete the 5S1 / 2 to 5D5 / 2 two-photon transition and generate 420nm blue fluorescence; The blue fluorescence is focused by the first plano-convex lens (4) to form focused fluorescence; stray light is filtered from the focused fluorescence by the 420nm filter (3) to obtain filtered fluorescence; the filtered fluorescence is converted into an amplified electrical signal by the photomultiplier tube (2) and transmitted to the frequency stabilization servo module (25); the frequency stabilization servo module (25) performs phase-locked amplification on the electrical signal to generate a frequency feedback control signal and transmits it to the external cavity semiconductor laser (11); the external cavity semiconductor laser (11) adjusts the laser emission frequency according to the frequency feedback control signal to achieve locking of the laser frequency with the two-photon transition frequency of rubidium 87 atoms.

9. The rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement according to claim 8, characterized in that, The first photodetector (10) detects the laser power transmitted to the second high-reflectivity mirror (9) and converts it into a power electrical signal, which is then transmitted to the power stabilization module (24). The power stabilization module (24) generates a power feedback control signal based on the power electrical signal and transmits it to the piezoelectric ceramic (6). The piezoelectric ceramic (6) fine-tunes the position of the optical element based on the power feedback control signal, thereby controlling the laser power.

10. The rubidium two-photon optical clock processing method based on single laser excitation and cavity enhancement according to claim 9, characterized in that, An optical frequency comb (23) emits a 1556.2nm fundamental frequency light; the fundamental frequency light is focused by a third plano-convex lens (22) and transmitted to a periodically polarized lithium niobate crystal (21); the focused fundamental frequency light is frequency-doubled by the periodically polarized lithium niobate crystal (21) to generate a 778.1nm frequency-doubled light; the frequency-doubled light is collimated by a second plano-convex lens (20) and transmitted to a second reflector (19); the frequency-doubled light is combined with the vertically polarized laser transmitted to the second reflector (19) to generate a combined laser and transmitted to a second photodetector (18); the combined laser is detected by the second photodetector (18) and converted into an electrical signal to achieve calibration and evaluation of the laser frequency.

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