Two-photon rubidium clock fluorescence collection system based on parabolic reflection cavity

Abstract

The invention relates to a two-photon rubidium clock fluorescence collection system based on a parabolic reflection cavity. The system comprises a rubidium atom gas chamber, a light collecting lens group, an optical filter and a photoelectric detector. The rubidium atom gas chamber is a parabolic reflection cavity with a truncated top end plane, and the truncated top end plane is a rubidium atom polling light entrance port and is plated with a color separation film for transmitting polling light and reflecting atomic fluorescence; the bottom end is an atomic fluorescence exit port and is plated with a color separation film for reflecting polling light and transmitting atomic fluorescence; the inner wall is plated with an atomic fluorescence reflecting film, rubidium atom steam is arranged in the cavity, and the cavity focus is located in a preset action area of the polling light and the rubidium atom steam. A first lens of the light collecting lens group converges atomic fluorescence, an object space focus of a second lens coincides with an image space focus of the first lens, and the converged fluorescence is collimated. The optical filter is used for filtering stray light with non-target wavelength and only allowing atomic fluorescence to penetrate; and the photoelectric detector converts the filtered fluorescence into an electric signal. The system can improve the optical energy utilization rate and the fluorescence collection efficiency.

Description

Technical Field

[0001] This application relates to the field of atomic frequency standard technology, and in particular to a two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity. Background Technology

[0002] An atomic clock is a precision time and frequency instrument that uses the transition frequency between different energy levels of atoms as a reference to lock the local oscillator frequency to that transition frequency, thereby generating a stable, high-precision time and frequency signal. The high precision, high stability, and portable integration of miniature atomic clocks make them widely used in fields such as communications and satellite navigation. Rubidium atomic clocks based on two-photon transitions have a simple structure, and the miniaturization and commercialization of the components used are relatively mature, showing promise for achieving high performance with smaller size and power consumption, and possessing great practical potential.

[0003] In a two-photon rubidium atomic clock, rubidium atomic vapor exists within a rubidium bulb, with atoms in the ground state 5S. 1 / 2 Rubidium atoms absorb two photons of the same frequency but opposite propagation direction from the same laser, exciting them to 5D. 5 / 2 state, then via 6P 3 / 2 Falling back to ground state 5S 1 / 2 The atom emits fluorescence at a wavelength of 420 nm. By collecting and detecting the fluorescence of this atom, information about the two-photon transition spectrum can be obtained, which in turn generates an error signal for frequency locking. This error signal is then used to achieve precise frequency stabilization control of the laser via a feedback control unit. This two-photon transition technique, through a suitable configuration, can eliminate the Doppler broadening of atomic transition spectrum lines, making the linewidth close to the natural linewidth of the atom. This allows for performance higher than that of ordinary thermal atomic clocks.

[0004] The frequency stabilization control signal of the laser comes from the transition spectral signal obtained by atomic fluorescence detection. The signal-to-noise ratio of the transition spectral signal is one of the key factors affecting the performance of the atomic clock. However, the fluorescence intensity of atomic radiation is very weak, so a highly sensitive sensor such as a photomultiplier tube is generally required for detection. In addition, a special fluorescence collection device needs to be designed to improve the fluorescence collection efficiency.

[0005] The fluorescence collection device of a typical two-photon rubidium clock is achieved by placing a lens group outside the rubidium bulb, which wastes fluorescence at angles outside the collection direction of the lens group, or it is designed based on a cubic rubidium bulb structure. The rubidium bulb is generally a hollow cubic structure made of optical glass, with rubidium vapor stored inside and saturated vapor pressure maintained. The 778 nm interrogation light is incident on the light-incident surface of the rubidium bulb (rubidium atom interrogation light inlet 11, coated with a dichroic film with 778 nm transmission and 420 nm reflection), and is reflected back along the original path on its opposite surface (atomic fluorescence outlet 12, coated with a dichroic film with 778 nm reflection and 420 nm transmission) to complete antiparallel interrogation. All other surfaces are coated with a 420 nm reflective film. In this way, the 420 nm atomic fluorescence generated by the two-photon transition can only be emitted from the atomic fluorescence outlet 12. After transmission, it is collected by the lens and filtered by the filter before being detected by the photoelectric sensor.

[0006] Atomic fluorescence is generated in the interaction region between the interrogation light and the rubidium vapor, similar to a cylindrical light source. Within the cubic reflection cavity formed by the rubidium bulb, the fluorescence undergoes complex reflections. Therefore, the light emitted from the atomic fluorescence emission port 12 is highly divergent. At the same time, in order to ensure the compact structure of the system, the lens system behind the emission surface cannot be designed with a complex structure to collect and converge the fluorescence. This greatly limits the fluorescence collection efficiency and the signal-to-noise ratio of the transition spectral signal of the entire system. Summary of the Invention

[0007] Therefore, it is necessary to provide a two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity to address the aforementioned technical problems.

[0008] A two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity, the system comprising:

[0009] The rubidium atom gas chamber, light-collecting lens group, filter and photodetector are arranged in sequence; The rubidium atom gas chamber is a parabolic reflective cavity with a top cut-off plane. The top cut-off plane is the rubidium atom probing light entrance, coated with a dichroic film that transmits the rubidium atom probing light and reflects atomic fluorescence. The bottom end is the atomic fluorescence exit port, coated with a dichroic film that reflects the rubidium atom probing light and transmits atomic fluorescence. The inner wall of the parabolic cavity is coated with an atomic fluorescence reflective film, and the interior contains rubidium atom vapor. The focal point of the parabolic reflective cavity is located in the predetermined interaction area between the rubidium atom probing light and the rubidium atom vapor within the gas chamber. The light-collecting lens group includes a first lens and a second lens arranged in sequence. The first lens is used to converge atomic fluorescence, and the object-side focal point of the second lens coincides with the image-side focal point of the first lens, which is used to collimate and converge the atomic fluorescence. The filter is used to filter stray light of non-target atomic fluorescence wavelengths, allowing only atomic fluorescence to pass through; The photodetector is used to receive filtered atomic fluorescence and convert it into an electrical signal, which is used for the laser frequency stabilization control of the two-photon rubidium clock.

[0010] In one embodiment, the rubidium atom gas chamber is made of optical glass.

[0011] In one embodiment, the preset action area is distributed along the axis of symmetry of the parabolic reflective cavity.

[0012] In one embodiment, the first lens is a spherical convex lens.

[0013] In one embodiment, the spherical convex lens has a symmetrical biconvex structure and is made of optical glass. Both convex surfaces of the spherical convex lens are coated with an anti-reflection film targeting the fluorescence wavelength of the target atom.

[0014] In one embodiment, the second lens is a spherical plano-convex lens.

[0015] In one embodiment, the spherical plano-convex lens is made of optical glass, with its convex surface facing the first lens and its flat surface facing the filter. The flat surface is coated with a reflective film targeting the fluorescence wavelength of the target atom.

[0016] In one embodiment, the filter is an interference-type narrowband filter.

[0017] In one embodiment, the photodetector is a photomultiplier tube or a photon counter.

[0018] The aforementioned two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity, by setting the rubidium atom gas cell as a parabolic reflector cavity with a truncated top, and placing the parabolic focal point at a predetermined interaction region between the probe light and the rubidium atom vapor, and by setting an inner wall atomic fluorescence reflective film and dichroic films at the entrance and exit, allows the atomic fluorescence to initially converge within the gas cell and has a certain shaping effect, significantly reducing the divergence during emission and improving optical energy utilization. The atomic fluorescence is then converged by the first lens in the light-collecting lens group, and the second lens (object-side focal point) further converges the atomic fluorescence. (By aligning the focal point with the image side of the first lens), the fluorescence is collimated, further compressing the fluorescence divergence angle and aperture without the need for complex lens structures, thus improving fluorescence collection efficiency. Stray light of non-target atomic fluorescence wavelengths is filtered out by a filter, and the fluorescence is converted into an electrical signal for laser frequency stabilization control using a photodetector. This reduces stray light interference and improves the signal-to-noise ratio of transition spectral signals. Simultaneously, the rubidium atom gas cell itself functions as a reflective cavity, reducing the need for additional reflective components and allowing for a more compact overall system structure, which is beneficial for the miniaturization and integration of two-photon rubidium clocks. This invention improves the system's optical energy utilization and fluorescence collection efficiency. Attached Figure Description

[0019] Figure 1 This is an application scenario diagram of a two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity in one embodiment; Figure 2 This is a schematic diagram and comparison of the light intensity distribution on the light-emitting surface of a cubic reflective cavity in one embodiment, wherein... Figure 2 (a) is a schematic diagram of the light trajectory distribution on the light-emitting surface of the cubic reflective cavity. Figure 2 (b) is a schematic diagram showing the distribution of radiation intensity as a function of angle at the light-emitting surface of the cubic reflector cavity. Figure 2 (c) is a schematic diagram of the distribution of incoherent irradiance on the light-emitting surface of the cubic reflector cavity as a function of spatial location; Figure 3 This is a schematic diagram and comparison of the light intensity distribution on the light-emitting surface of the spherical reflecting cavity in one embodiment, wherein... Figure 3 (a) is a schematic diagram of the light trajectory distribution on the light-emitting surface of the spherical reflecting cavity. Figure 3 (b) is a schematic diagram showing the distribution of radiation intensity from the light-emitting surface of the spherical reflecting cavity as a function of angle. Figure 3 (c) is a schematic diagram of the distribution of incoherent irradiance on the light-emitting surface of the spherical reflector as a function of spatial position; Figure 4 This is a schematic diagram and comparison of the light intensity distribution of the three types of reflective cavities on a parabolic surface in one embodiment. Figure 4 (a) is a schematic diagram of the light trajectory distribution on the light-emitting surface of the parabolic reflector cavity. Figure 4 (b) is a schematic diagram showing the distribution of radiation intensity at the light-emitting surface of the parabolic reflector cavity as a function of angle. Figure 4 (c) is a schematic diagram of the distribution of incoherent irradiance on the light-emitting surface of the parabolic reflector cavity with spatial position; Figure 5 This is a schematic diagram of a fluorescence collection optical path model based on three types of reflecting cavities: cube, sphere, and paraboloid, in one embodiment. Figure 5 (a) is a schematic diagram of the fluorescence collection optical path model of a cubic reflective cavity. Figure 5 (b) is a schematic diagram of the fluorescence collection optical path model of the spherical reflector cavity. Figure 5 (c) is a schematic diagram of the fluorescent collection optical path model of the parabolic reflector cavity; Figure 6 This is a schematic diagram comparing the light intensity distribution at the image plane of the photodetector 40 of an atomic fluorescence collection system employing three types of reflective cavities: cubic, spherical, and parabolic. Figure 6 (a) is a schematic diagram comparing the light intensity distribution of the cubic reflective cavity. Figure 6 (b) is a schematic diagram comparing the light intensity distribution of the spherical reflecting cavity. Figure 6 (c) is a schematic diagram comparing the light intensity distribution of the parabolic reflector cavity.

[0020] Explanation of reference numerals in the attached figures: Rubidium atom gas chamber 10, rubidium atom probing light inlet 11, atomic fluorescence outlet 12, light-collecting lens group 20, first lens 21, second lens 22, filter 30, photodetector 40. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] In existing two-photon rubidium clocks, the rubidium atom gas cells are mostly cubic structures. The fluorescence collection device either places a mirror and lens group outside the rubidium atom gas cell for direct collection, or forms a cubic reflection cavity with the rubidium atom gas cell and then collects the fluorescence with a lens group. The former wastes fluorescence energy in directions outside the mirror group or has too many components, affecting the compact structure. The latter forms very complex reflections within the reflection cavity, resulting in a high degree of divergence of the emitted light. Since the aperture of the photodetector is limited, and the transmittance of the interference filter is closely related to the incident angle, it is difficult for the subsequent optical system to collect and converge the light into a small beam for the photodetector to receive using a simple lens group.

[0023] Based on the properties of a parabola, light rays passing through its focal point are reflected by the parabola and then emitted parallel to its axis of symmetry. This invention utilizes such a parabolic reflective cavity in a two-photon rubidium clock, allowing the probe light to enter and return along the parabolic axis of symmetry. In this way, while reflecting atomic fluorescence towards the exiting surface, the reflecting surface can also perform preliminary focusing and shaping of the diverging atomic fluorescence, reducing the divergence of the emitted light. This allows for high-efficiency fluorescence collection using a simple lens system.

[0024] In one embodiment, such as Figure 1 As shown, a two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity is provided, comprising: The rubidium atom gas chamber 10, the light-collecting lens group 20, the filter 30 and the photodetector 40 are arranged sequentially. The rubidium atom gas chamber 10 is a parabolic reflective cavity with a top cut-off plane. The top cut-off plane is the rubidium atom probing light inlet 11, which is coated with a dichroic film that transmits the rubidium atom probing light and reflects atomic fluorescence. The bottom end is the atomic fluorescence outlet 12, which is coated with a dichroic film that reflects the rubidium atom probing light and transmits atomic fluorescence. The inner wall of the parabolic cavity is coated with an atomic fluorescence reflective film, and the cavity contains rubidium atom vapor. The focal point of the parabolic reflective cavity is located in the preset interaction area between the rubidium atom probing light and the rubidium atom vapor in the gas chamber. The light-gathering lens group 20 includes a first lens 21 and a second lens 22 arranged in sequence. The first lens 21 is used to converge atomic fluorescence, and the object-side focal point of the second lens 22 coincides with the image-side focal point of the first lens 21, which is used to collimate and converge the atomic fluorescence. Filter 30 is used to filter stray light of non-target atomic fluorescence wavelengths, allowing only atomic fluorescence to pass through; The photodetector 40 is used to receive filtered atomic fluorescence and convert it into an electrical signal, which is used for the frequency stabilization control of the laser in the two-photon rubidium clock.

[0025] In the aforementioned two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity, by setting the rubidium atom gas chamber 10 as a parabolic reflector cavity with a truncated top, and placing the parabolic focal point at a predetermined interaction region between the probe light and the rubidium atom vapor, and by setting an inner wall atomic fluorescence reflective film and dichroic films at the entrance and exit, the atomic fluorescence can be initially focused within the gas chamber, and a certain shaping effect is achieved, significantly reducing the divergence during emission and improving the optical energy utilization rate. The atomic fluorescence is then focused by the first lens 21 in the light-collecting lens group 20, and the second lens 22 (object side) focuses the atomic fluorescence. (The focal point coincides with the image-side focal point of the first lens 21) collimates the fluorescence, further compressing the fluorescence divergence angle and aperture without the need for a complex lens structure, thus improving fluorescence collection efficiency. Stray light of non-target atomic fluorescence wavelengths is filtered by filter 30, and the fluorescence is converted into an electrical signal by photodetector 40 for laser frequency stabilization control, reducing stray light interference and improving the signal-to-noise ratio of transition spectral signals. Simultaneously, the rubidium atom gas cell 10 itself serves as a reflective cavity, reducing additional reflective components and allowing for a more compact overall system structure, which is beneficial for the miniaturization and integration of two-photon rubidium clocks. This embodiment of the invention can improve the system's optical energy utilization and fluorescence collection efficiency.

[0026] like Figure 1 As shown, the system includes a rubidium atom gas chamber 10, a first lens 21, a second lens 22, a filter 30, and a photodetector 40. The rubidium atom gas chamber 10 interacts with the Rb atom probing light and serves as a reflecting cavity. The first lens 21 and the second lens 22 combine to form a light-collecting optical path, used to collect atomic fluorescence and compress the divergence angle and aperture of the atomic fluorescence for easy incident on the photodetector 40. The filter 30 filters out other stray light, allowing only atomic fluorescence to pass through, and is located after the light-collecting optical path. The photodetector 40 detects atomic fluorescence and converts it into an electrical signal. The rubidium atom gas chamber 10 is designed as a truncated parabolic shape, with a flat top corresponding to the rubidium atom probing light inlet 11 shown in the figure, and a flat bottom corresponding to the atomic fluorescence outlet 12 shown in the figure. The top flat surface is coated with a dichroic film that transmits the probing light and reflects the atomic fluorescence, the bottom flat surface is coated with a dichroic film that reflects the probing light and transmits the atomic fluorescence, and the parabolic surface on the side is coated with an atomic fluorescence reflective film.

[0027] In one embodiment, the rubidium atom gas chamber 10 is made of optical glass. In this embodiment, the rubidium atom gas chamber 10 is made of optical glass, which can ensure efficient transmission of 420nm atomic fluorescence, while having good sealing performance. It can stably maintain the saturated vapor pressure of rubidium atom vapor in the gas chamber, avoiding fluorescence energy loss due to poor light transmittance of the material, or affecting the two-photon transition efficiency due to insufficient sealing.

[0028] In one embodiment, the preset action area is distributed along the axis of symmetry of the parabolic reflective cavity.

[0029] In this embodiment, the preset active area is distributed along the axis of symmetry of the parabolic reflective cavity, which ensures that the interaction between the rubidium atom probing light and the rubidium atom vapor is concentrated near the axis of symmetry. This area coincides with the focal point of the parabolic surface, which allows the atomic fluorescence to achieve convergence by making maximum use of the optical properties of the parabolic surface, significantly reducing the degree of fluorescence divergence during emission, and laying the foundation for the efficient collection of the subsequent light-collecting lens group 20.

[0030] Specifically, a 778 nm interrogation beam is incident perpendicularly from the rubidium atom interrogation beam inlet 11. After reaching the atomic fluorescence outlet 12, it is reflected back along the same path, forming an antiparallel interrogation beam. This beam interacts with the rubidium atom vapor in the gas chamber, resulting in a two-photon transition and emitting 420 nm atomic fluorescence. The atomic fluorescence is generated in the region where the interrogation beam interacts with the rubidium atoms, and can be approximated as originating from a cylindrical light source emitting light into the entire spherical space. Based on the characteristics of a parabola, light rays originating from the focal point are reflected by the parabola and emitted parallel to the axis of symmetry. For a cylindrical atomic fluorescence source located at the axis of symmetry of the parabola, the light at the focal point is naturally perfectly collimated and emitted parallel to the axis of symmetry. Although the fluorescence outside the focal point is not perfectly collimated, compared to ordinary cubic or spherical reflecting cavities, the emission angle is reduced, significantly lowering the divergence angle of the light rays from the bottom emission surface.

[0031] In one embodiment, the first lens 21 is a spherical convex lens.

[0032] In one embodiment, the spherical convex lens has a symmetrical biconvex structure and is made of optical glass. Both convex surfaces of the spherical convex lens are coated with an anti-reflection film targeting the fluorescence wavelength of the target atom.

[0033] In this embodiment, as Figure 1 As shown, in this invention, after the atomic fluorescence is emitted from the parabolic reflection cavity through the atomic fluorescence emission port 12, it first passes through the first lens 21 for focusing. The lens is coated with an anti-reflection film for the atomic fluorescence wavelength to improve transmittance. The lens material is selected as optical glass with a high refractive index and has a symmetrical biconvex structure. This achieves the purpose of shortening the focal length, enhancing the focusing ability, and thus reducing the overall length of the system.

[0034] In one embodiment, the second lens 22 is a spherical plano-convex lens.

[0035] In one embodiment, the spherical plano-convex lens is made of optical glass, with the convex surface facing the first lens 21 and the flat surface facing the filter 30, and the flat surface is coated with a reflective film targeting the fluorescence wavelength of the target atom.

[0036] In this embodiment, the atomic fluorescence light is converged by the first lens 21 and then enters the second lens 22. The image-side focal point of the first lens 21 and the object-side focal point of the second lens 22 coincide. The second lens 22 thus collimates the light and compresses the beam diameter. The smaller diameter and lower divergence of the beam make it easier for the photodetector 40 to receive the light. The second lens 22 is also made of optical glass with a high refractive index to shorten the focal length and reduce the system length. However, it has a plano-convex structure, where the light enters from the curved surface and exits from the flat surface. The flat surface can reflect the light reflected back by subsequent optical devices, increasing the utilization rate of light energy.

[0037] In one embodiment, filter 30 is an interference-type narrowband filter.

[0038] In this embodiment, atomic fluorescence exits from the second lens 22 and enters the filter 30, allowing only 420 nm atomic fluorescence to pass through, thus avoiding stray light interference with the measurement, such as the 778 nm interrogation light exiting from the atomic fluorescence exit port 12. The filter 30 is an interference-type narrowband filter, which has a narrower bandwidth, higher transmittance, and stronger environmental adaptability. The transmittance of the interference-type narrowband filter is related to the incident angle, therefore it is placed after the first lens 21 and the second lens 22 of the collimating optical system.

[0039] In one embodiment, the photodetector 40 is a photomultiplier tube or a photon counter.

[0040] In this embodiment, after passing through the filter 30, the atomic fluorescence enters the photodetector 40, and the output electrical signal is used for feedback control of the atomic clock system. Because the intensity of the atomic fluorescence is weak, the photodetector 40 is selected from devices with high gain and good response linearity, such as a photomultiplier tube.

[0041] like Figures 2-4 As shown, a schematic diagram and comparison of the light intensity distribution at the light-emitting surfaces of three types of reflecting cavities—cubic, spherical, and parabolic—are presented. Specifically, the simulation using optical simulation software demonstrates the distribution of radiation intensity with angle and irradiance with spatial position at the light-emitting surfaces of these three cavities. In the simulation, the maximum aperture of all reflecting cavities remains consistent, and the atomic fluorescence light source is identical. The insufficient length of the spherical cavity is compensated for by a cylinder. It can also be seen that the emitted light from the parabolic reflecting cavity has lower divergence and is more concentrated.

[0042] like Figure 5 As shown, a schematic diagram of a fluorescence collection optical path model based on three types of reflecting cavities—cubic, spherical, and parabolic—is presented. The lens group structures behind the three systems are identical. Ray tracing simulations are then performed on each system, and the irradiance distribution of the 40-image plane of the photodetector is compared. The simulation comparison results are as follows: Figure 4 As shown.

[0043] Figure 6 A schematic diagram comparing the light intensity distribution at the image plane of the photodetector 40 in an atomic fluorescence collection system employing three types of reflective cavities: cubic, spherical, and parabolic. As can be seen from the diagram, among the three reflective cavities, the parabolic reflective cavity has the strongest light-converging ability, and the irradiance of the detector image plane is the most concentrated and highest, making it more convenient for the photodetector 40 to receive and detect light.

[0044] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A two-photon rubidium clock fluorescence collection system based on a parabolic reflector cavity, characterized in that, The system includes a rubidium atom gas chamber, a light-collecting lens group, a filter and a photodetector arranged in sequence. The rubidium atom gas chamber is a parabolic reflective cavity with a top cut-off plane. The top cut-off plane is the rubidium atom probing light entrance, coated with a dichroic film that transmits the rubidium atom probing light and reflects atomic fluorescence. The bottom end is the atomic fluorescence exit port, coated with a dichroic film that reflects the rubidium atom probing light and transmits atomic fluorescence. The inner wall of the parabolic cavity is coated with an atomic fluorescence reflective film, and the interior contains rubidium atom vapor. The focal point of the parabolic reflective cavity is located in the predetermined interaction area between the rubidium atom probing light and the rubidium atom vapor within the gas chamber. The light-collecting lens group includes a first lens and a second lens arranged in sequence. The first lens is used to converge atomic fluorescence, and the object-side focal point of the second lens coincides with the image-side focal point of the first lens, which is used to collimate and converge the atomic fluorescence. The filter is used to filter stray light of non-target atomic fluorescence wavelengths, allowing only atomic fluorescence to pass through; The photodetector is used to receive filtered atomic fluorescence and convert it into an electrical signal, which is used for the laser frequency stabilization control of the two-photon rubidium clock.

2. The system according to claim 1, characterized in that, The rubidium atom gas chamber is made of optical glass.

3. The system according to claim 1, characterized in that, The preset operating area is distributed along the axis of symmetry of the parabolic reflective cavity.

4. The system according to claim 1, characterized in that, The first lens is a spherical convex lens.

5. The system according to claim 4, characterized in that, The spherical convex lens has a symmetrical biconvex structure and is made of optical glass. Both convex surfaces of the spherical convex lens are coated with an anti-reflection film targeting the fluorescence wavelength of the target atom.

6. The system according to claim 1, characterized in that, The second lens is a spherical plano-convex lens.

7. The system according to claim 6, characterized in that, The spherical plano-convex lens is made of optical glass. The convex surface of the spherical plano-convex lens faces the first lens, and the flat surface faces the filter. The flat surface is coated with a reflective film targeting the fluorescence wavelength of the target atom.

8. The system according to claim 1, characterized in that, The filter is an interference-type narrowband filter.

9. The system according to claim 1, characterized in that, The photodetector is a photomultiplier tube or a photon counter.

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