Reflection type two-photon rubidium clock atomic fluorescence collection system

Abstract

The invention relates to a reflective two-photon rubidium clock atomic fluorescence collection system. The system comprises a rubidium atom gas chamber, a reflector, an optical filter, a lens and a photoelectric detector. The rubidium atom gas chamber is a reflection cavity with a parabolic cylinder structure, the side plane of the rubidium atom gas chamber is a polling light incident plane and is plated with a color separation film for transmitting polling light and reflecting atomic fluorescence, and the polling light incident point is located at the focal point of the parabolic section; the opposite plane of the parabolic cylinder of the reflection cavity is an atomic fluorescence emergent surface, the inner wall of the parabolic cylinder is plated with an atomic fluorescence reflecting film, rubidium atom steam is contained in the parabolic cylinder, and a preset included angle is formed between the reflector and the atomic fluorescence emergent surface and used for reflecting a light path to enable a fluorescence collection light path and a polling light path to be arranged in parallel and converging emergent atomic fluorescence. The optical filter filters stray light with non-target wavelength, the lens converges atomic fluorescence after light filtering, the photoelectric detector receives the fluorescence and converts the fluorescence into an electric signal, and frequency stabilization control of the laser is achieved. By adopting the system, the space utilization rate, the system signal-to-noise ratio and the fluorescence collection efficiency can be improved.

Description

Technical Field

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

[0002] Atomic clocks are currently the most precise time and frequency measuring instruments, widely used in communication, navigation, scientific research, and precision metrology. Miniaturization has always been a key research direction in the field of atomic clocks. High precision and high stability combined with a small integrated structure allow them to be mounted on more platforms and expand into more application scenarios. Two-photon rubidium clocks utilize the two-photon transitions of rubidium atoms, eliminating the interference of Doppler frequency shift in the atomic transition spectrum. This allows them to achieve higher performance than ordinary thermal atomic clocks. Furthermore, their simple structure and mature components make them one of the most promising types of miniature atomic clocks for practical application.

[0003] In a two-photon rubidium clock, a highly stable laser serves as the local oscillator, providing the probe light required for atomic transitions. This probe light is transmitted through a rubidium atom gas cell and then reflected back along its original path. The rubidium atoms in the gas cell absorb two photons of the same wavelength but propagating in opposite directions, transitioning from 5S... 1 / 2 ground state excited to 5D 5 / 2 Excited state, excited state atoms via 6P 3 / 2 During the transition from the intermediate state to the ground state, a 420 nm photon is emitted. The 420 nm atomic fluorescence collection and detection is used to generate an error signal for frequency locking control. This error signal is then used to precisely stabilize the laser's frequency via a feedback control unit, and finally, a clock signal is output via an optical comb. The two-photon rubidium clock generates the laser's frequency stabilization control signal based on the atomic transition spectrum signal. Therefore, the signal-to-noise ratio of the atomic fluorescence collection and detection is one of the key factors affecting clock performance. Generally, a dedicated fluorescence collection optical path is used, along with a high-gain photodetector such as a photomultiplier tube, to achieve high-efficiency atomic fluorescence collection.

[0004] Currently, two-photon rubidium clocks typically collect fluorescence by placing a lens array outside a rubidium atomic cell. However, the emission direction of atomic fluorescence is highly divergent, which wastes a significant amount of fluorescence energy outside the lens array's collection direction. Another method uses a rubidium atomic cell as a reflective cavity. The rubidium atomic cell is cubic in shape, with the side where the probing light is incident (denoted as S)... a The surface is coated with a dichroic film that transmits 778 nm interrogative light and reflects 420 nm atomic fluorescence. a The opposite of (denoted as S) b One side is coated with a dichroic film that reflects 778 nm and transmits 420 nm, while the other four sides are coated with a 420 nm high-reflectivity film. Thus, S... bThe surface can reflect the incident laser to form an antiparallel interrogation process, while the rubidium atom gas cell forms a cubic reflecting cavity, and the 420 nm atomic fluorescence can only be detected from the S... b For surface-emitting fluorescence, effective collection can be achieved by placing an external lens assembly. While this method avoids wasting atomic fluorescence from other emission angles, the emission angle of the light at the cubic reflector cavity exit is complex and divergent. Furthermore, the external lens assembly, for the sake of miniaturization and integration of the atomic clock, must adopt a simple structure, thus limiting the light compression effect and restricting the overall collection efficiency of the fluorescence collection system. Besides the limitation on collection efficiency, in both of the above collection methods, the fluorescence collection optical path is located perpendicular to the laser interrogation optical path (in the first collection method) or later (in the second collection method), resulting in a relatively large overall optical path length or volume. Summary of the Invention

[0005] Therefore, it is necessary to provide a reflective two-photon rubidium clock atomic fluorescence collection system to address the aforementioned technical problems.

[0006] A reflective two-photon rubidium clock atomic fluorescence collection system, the system comprising: The rubidium atom gas chamber, mirror, filter, lens, and photodetector are arranged sequentially. The rubidium atom gas chamber is a reflective cavity with a parabolic cylindrical structure. The side plane of the reflective cavity is the incident surface of the interrogation light and is coated with a dichroic film that transmits the interrogation light and reflects atomic fluorescence. The incident point of the interrogation light is located at the focal point of the parabolic section. The opposing plane of the parabolic cylinder of the reflective cavity is the atomic fluorescence exit surface. The inner wall of the parabolic cylinder is coated with an atomic fluorescence reflective film and contains rubidium atom vapor. The reflector is set at a preset angle to the atomic fluorescence emission surface, which is used to deflect the light path so that the fluorescence collection light path and the interrogation light path are parallel and side by side, and to converge the emitted atomic fluorescence. The filter is used to filter stray light of non-target atomic fluorescence wavelengths; The lens is used to converge filtered atomic fluorescence; The photodetector is used to receive filtered atomic fluorescence and convert it into an electrical signal to achieve laser frequency stabilization control.

[0007] In one embodiment, the rubidium atom gas chamber is made of optical glass.

[0008] In one embodiment, the reflective cavity has a film layer on the opposite side plane to the interrogation light incident surface coated with a film layer to reflect the interrogation light in order to form an antiparallel interrogation process.

[0009] In one embodiment, the incident point of the interrogation light coincides with the axial center of the reflective cavity.

[0010] In one embodiment, the reflector is a parabolic reflector.

[0011] In one embodiment, the preset angle between the reflector and the atomic fluorescence emission surface is 45°.

[0012] In one embodiment, the filter is an interference-type narrowband filter.

[0013] In one embodiment, the lens is a spherical convex lens; the surface of the spherical convex lens is coated with an antireflection film targeting the fluorescence wavelength of the target atom.

[0014] In one embodiment, the lens is arranged parallel to the filter, and the effective aperture of the lens is not less than the aperture of the atomic fluorescence emission surface.

[0015] In one embodiment, the photodetector is a photomultiplier tube or a photon counter.

[0016] The aforementioned reflective two-photon rubidium clock atomic fluorescence collection system, by designing the rubidium atom gas cell as a parabolic cylindrical reflective cavity, combined with the interrogation light incident point located at the focal point of the parabolic section, the inner wall of the parabolic cylinder coated with an atomic fluorescence reflective film, and the incident surface coated with a dichroic film, allows for initial shaping of the atomic fluorescence within the cavity, reducing outgoing divergence and laying the foundation for subsequent collection. By setting the reflector at a predetermined angle to the atomic fluorescence exit surface, the optical path can be deflected to make the fluorescence collection path parallel and juxtaposed with the interrogation path, compressing the overall system volume, and also enabling secondary focusing of the outgoing fluorescence, improving collection efficiency. By filtering stray light of non-target atomic fluorescence wavelengths through a filter, and focusing the filtered fluorescence with a lens, the signal is then converted into an electrical signal by a photodetector, reducing stray light interference, ensuring signal quality, and providing precise input for laser frequency stabilization control. This invention comprehensively covers the core requirements of efficient fluorescence collection, system miniaturization and integration, and signal quality assurance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a reflective two-photon rubidium clock atomic fluorescence collection system in one embodiment; Figure 2 This is a schematic diagram of the rubidium atom gas chamber structure in one embodiment; Figure 3 This is a schematic diagram of a fluorescence collection simulation example structure in one embodiment, wherein, Figure 3 (a) is a schematic diagram of the optical path and structure of the fluorescence collection system of the present invention. Figure 3 (b) is a schematic diagram of the three-dimensional structure and optical path distribution of the fluorescence collection system of the present invention; Figure 4 This is a schematic diagram of the detector surface radiation intensity and irradiance in one embodiment, wherein, Figure 4(a) is a schematic diagram of the radiation intensity distribution on the detector surface. Figure 4 (b) is a schematic diagram of the incoherent irradiance distribution on the detector surface; Figure 5 This is a simulation example of a conventional cubic reflective cavity and a non-folding optical collection path, along with a schematic diagram of the detector surface irradiance in one embodiment. Figure 5 (a) is a schematic diagram of the structure and optical path of a conventional cubic reflective cavity for collecting light without deflection. Figure 5 (b) is a schematic diagram of the incoherent irradiance distribution on the detector surface of a conventional cubic reflective cavity without a deflection-based optical path. Explanation of reference numerals in the attached figures: Rubidium atom gas chamber 10, reflector 20, filter 30, lens 40, photodetector 50. Detailed Implementation

[0018] 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.

[0019] Currently, the rubidium atomic gas cells used in two-photon rubidium clock systems are mostly cubic structures. The fluorescence collection device either places a lens group outside the rubidium atomic gas cell for direct collection, or forms a cubic reflection cavity with the rubidium atomic gas cell, and then uses a lens group to collect the light at the exit surface of the reflection cavity. The former wastes fluorescence energy outside the lens aperture, while the latter creates very complex reflections within the reflection cavity, resulting in high divergence and complex exit angles of the light at the exit port. The subsequent lens group cannot achieve effective light convergence through a simple structure, compressing the light into a thin, straight beam that is easy for the photodetector to receive, thus limiting the overall collection efficiency of the system.

[0020] To address the above problems, this invention proposes a reflective fluorescence collection system. The laser probing light path and the fluorescence collection light path are placed parallel to each other, compressing the overall system volume and facilitating the miniaturized integrated structure design of the clock system. Specifically, the rubidium atom gas cell 10 is designed as a parabolic cylindrical reflective cavity. The probing light is incident perpendicularly to the side of the gas cell at the focal point of the parabola. Thus, the interaction region between the atoms and the probing light (i.e., the light source region for 420 nm atomic fluorescence) is located at the focal point of the parabola. Based on the properties of a parabola, the light emitted at the focal point is reflected and exits parallel to the parabolic axis of symmetry. This allows for preliminary shaping of the fluorescence at the light-emitting surface of the gas cell, resulting in less divergence. A simple external structure consisting of a reflector 20 and a lens 40 can achieve high-efficiency fluorescence collection.

[0021] In one embodiment, such as Figure 1 As shown, a reflective two-photon rubidium clock atomic fluorescence collection system is provided, comprising: The rubidium atom gas chamber 10, the reflector 20, the filter 30, the lens 40, and the photodetector 50 are arranged sequentially. The rubidium atom gas chamber 10 is a reflective cavity with a parabolic cylindrical structure. The side plane of the reflective cavity is the incident surface of the interrogation light and is coated with a dichroic film that transmits the interrogation light and reflects atomic fluorescence. The incident point of the interrogation light is located at the focal point of the parabolic section. The opposing plane of the parabolic cylinder of the reflective cavity is the atomic fluorescence emission surface. The inner wall of the parabolic cylinder is coated with an atomic fluorescence reflective film and contains rubidium atom vapor. The reflector 20 is set at a preset angle to the atomic fluorescence emission surface, which is used to deflect the light path so that the fluorescence collection light path and the interrogation light path are parallel and side by side, and to converge the emitted atomic fluorescence. The filter 30 is used to filter stray light of non-target atomic fluorescence wavelengths; The lens 40 is used to converge the filtered atomic fluorescence; The photodetector 50 is used to receive filtered atomic fluorescence and convert it into an electrical signal to achieve laser frequency stabilization control.

[0022] In the aforementioned reflective two-photon rubidium clock atomic fluorescence collection system, by designing the rubidium atom gas chamber 10 as a parabolic cylindrical reflective cavity, combined with the design of the probe light incident point located at the focal point of the parabolic section, the inner wall of the parabolic cylinder coated with an atomic fluorescence reflective film, and the incident surface coated with a dichroic film, the atomic fluorescence can be initially shaped within the cavity, reducing the degree of outgoing divergence and laying the foundation for subsequent collection. The reflector 20 is set at a preset angle to the atomic fluorescence emitting surface, which not only deflects the light path so that the fluorescence collection light path and the probe light path are parallel and juxtaposed, compressing the overall system volume, but also allows for secondary focusing of the emitted fluorescence, improving collection efficiency. The filter 30 filters stray light of non-target atomic fluorescence wavelengths, and the lens 40 focuses the filtered fluorescence, which is then converted into an electrical signal by the photodetector 50. This reduces stray light interference, ensures signal quality, and provides precise input for laser frequency stabilization control. This embodiment of the invention comprehensively covers the core requirements of efficient fluorescence collection, system miniaturization and integration, and signal quality assurance.

[0023] In one embodiment, the rubidium atom gas chamber 10 is made of optical glass.

[0024] In one embodiment, in the reflective cavity, the plane on the opposite side of the interrogation light incident surface is coated with a film layer that reflects the interrogation light, so as to reflect the interrogation light to form an anti-parallel interrogation process.

[0025] In this embodiment, as Figure 1As shown, the system of the present invention sequentially includes a rubidium atom gas chamber 10, a reflector 20, a filter 30, a lens 40, and a photodetector 50. The rubidium atom gas chamber 10 acts as a reflector in the optical path, converging and emitting the diverging fluorescence, which is then converged and compressed by the subsequent reflector 20 and lens 40 into a thin, straight beam that is easy for the photodetector 50 to receive.

[0026] like Figure 2 As shown, a schematic diagram of a rubidium atomic gas cell structure is provided. The rubidium atomic gas cell 10 is designed as a parabolic cylindrical shape and is made of optical glass. The parabolic cylindrical surface is denoted as surface S1 and is coated with a 420 nm atomic fluorescence reflective film. The side surface S2 serves as the laser incident surface and is coated with a dichroic film that transmits 778 nm interrogation light and reflects 420 nm atomic fluorescence. The side surface S3 can be coated with a reflective film that simultaneously reflects interrogation light and atomic fluorescence. This surface can be used to reflect interrogation light to form antiparallel interrogation, or it can be coated with a dichroic film that transmits interrogation light and reflects atomic fluorescence. The interrogation light is reflected by a reflector located behind surface S3. S1, S2, and S3 form a reflective cavity, and surface S4, which is opposite to surface S1, serves as the light-emitting surface of the reflective cavity.

[0027] In one embodiment, the incident point of the interrogation light coincides with the axial center of the reflecting cavity.

[0028] In this embodiment, the probe laser is incident perpendicularly to the S2 surface, and the intersection with the S2 surface is located at the focal point of the parabola. According to the properties of the parabola, the light rays originating from the focal point will be reflected by the parabola and then emitted parallel to the axis of symmetry of the parabola. Therefore, the parabolic reflective cavity can not only converge the light rays but also perform preliminary shaping of the light rays, reducing the divergence of the light rays from the light-emitting surface. This is more conducive to the subsequent optical system to collect the light. The light rays can be efficiently compressed through a simple structure.

[0029] In one embodiment, the reflector 20 is a parabolic reflector.

[0030] In one embodiment, the preset angle between the reflector 20 and the atomic fluorescence emission surface is 45°.

[0031] In this embodiment, combined with Figure 1 and Figure 2The atomic fluorescence optical path is described below. In this invention, after the atomic fluorescence is emitted from the light-emitting surface S4 of the rubidium atomic gas cell 10, it is first reflected by the reflector 20. The reflector 20 is placed at a 45° angle to the surface S4. After reflection, the optical path is parallel to but opposite to the incident direction of the probing laser. This allows the components of the probing optical path and the fluorescence collection optical path to be arranged in parallel, effectively reducing the length and volume of the optical path and facilitating the miniaturized integration design of the optical system. The reflector 20 is a concave reflector, which further focuses the fluorescence while refracting the optical path. The concave reflector is parabolic, providing stronger focusing ability and better collimation of the emitted light compared to ordinary spherical mirrors.

[0032] In one embodiment, the filter 30 is an interference-type narrowband filter.

[0033] In this embodiment, atomic fluorescence, after being refracted by mirror 20, enters filter 30. Filter 30 only allows atomic fluorescence with a wavelength of 420 nm to pass through, filtering out stray light of other wavelengths, such as the 778 nm stray light emitted from the S4 surface of the rubidium atom gas cell 10. 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 of light, so it is placed after mirror 20 and in front of lens 40, with the angle between filter 30 and mirror 20 being 45°.

[0034] In one embodiment, the lens 40 is a spherical convex lens; the surface of the spherical convex lens is coated with an antireflection film targeting the fluorescence wavelength of the target atom.

[0035] In one embodiment, the lens 40 is arranged parallel to the filter 30, and the effective aperture of the lens 40 is not less than the aperture of the atomic fluorescence emission surface.

[0036] In this embodiment, the atomic fluorescence, after being filtered by the filter 30, is focused and compressed by the lens 40 into a small beam that is easily received by the photodetector 50. The lens 40 is a spherical convex lens, made of optical glass with a high refractive index to enhance its focusing ability. An anti-reflection coating for a 420 nm wavelength is deposited on the surface of the lens 40 to increase the system transmittance.

[0037] In one embodiment, the photodetector 50 is a photomultiplier tube or a photon counter.

[0038] In this embodiment, the atomic fluorescence is focused by a convex lens and received by a photodetector 50. The photodetector 50 converts the fluorescence into an electrical signal output for feedback control of the atomic clock system. Because the intensity of atomic fluorescence is weak, the photodetector 50 is selected from devices with high gain and good response linearity, such as photomultiplier tubes or photon counters.

[0039] It is understood that in the system of this invention, the rubidium atom gas cell itself serves as a reflective cavity, from which atomic fluorescence at all angles is emitted, improving the fluorescence collection efficiency. Simultaneously, it allows for a more compact overall structure, facilitating miniaturization and integration. The reflective cavity is designed as a parabolic cylinder, which, while converging atomic fluorescence, also possesses a certain shaping effect, resulting in lower divergence of the emitted light. This allows the subsequent optical system to achieve high collection efficiency with a simpler structure, improving the system's signal-to-noise ratio. Using a reflector to deflect the optical path, with the laser probing optical path and the fluorescence collection optical path placed parallel and side-by-side, effectively compresses the length and volume of the optical system, making the overall system structure more compact and facilitating miniaturized integration design.

[0040] This invention verifies the fluorescence collection effect through experiments, such as... Figure 3 As shown, a schematic diagram of a fluorescence collection simulation example is provided, illustrating the structure of the optical system of this invention. Atomic fluorescence is generated and the region where the laser interacts with atoms is explored. The light source is set as a cylindrical light source with a diameter of 0.15 mm, located inside a cylindrical mirror. The system is set to single-wavelength incident light, therefore the filter is ignored in the simulation. The focal length of the parabolic cylinder in the rubidium atom gas chamber is 0.8 mm, the focal length of the parabolic mirror is 2.5 mm, the lens material is LASF35, and the spherical radius is 5 mm. The radiation intensity and irradiance received by the detector surface are as follows: Figure 4 As shown, Figure 5 The structure of the fluorescence collection optical path and the irradiance distribution of the detector surface are shown using a conventional cubic reflective cavity and a non-folding collection optical path. The comparison shows that this system can ensure high collection efficiency while facilitating miniaturized integration design.

[0041] 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.

[0042] 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 reflective two-photon rubidium clock atomic fluorescence collection system, characterized in that, The system includes a rubidium atom gas chamber, a reflector, a filter, a lens, and a photodetector arranged sequentially. The rubidium atom gas chamber is a reflective cavity with a parabolic cylindrical structure. The side plane of the reflective cavity is the incident surface of the interrogation light and is coated with a dichroic film that transmits the interrogation light and reflects atomic fluorescence. The incident point of the interrogation light is located at the focal point of the parabolic section. The opposing plane of the parabolic cylinder of the reflective cavity is the atomic fluorescence exit surface. The inner wall of the parabolic cylinder is coated with an atomic fluorescence reflective film and contains rubidium atom vapor. The reflector is set at a preset angle to the atomic fluorescence emission surface, which is used to deflect the light path so that the fluorescence collection light path and the interrogation light path are parallel and side by side, and to converge the emitted atomic fluorescence. The filter is used to filter stray light of non-target atomic fluorescence wavelengths; The lens is used to converge filtered atomic fluorescence; The photodetector is used to receive filtered atomic fluorescence and convert it into an electrical signal to achieve laser frequency stabilization control.

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, In the reflective cavity, the plane opposite to the incident surface of the interrogation light is coated with a film layer that reflects the interrogation light, so as to reflect the interrogation light to form an anti-parallel interrogation process.

4. The system according to claim 1, characterized in that, The incident point of the probing light coincides with the axial center of the reflecting cavity.

5. The system according to claim 1, characterized in that, The reflector is a parabolic reflector.

6. The system according to claim 1, characterized in that, The preset angle between the reflector and the atomic fluorescence emission surface is 45°.

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

8. The system according to claim 1, characterized in that, The lens is a spherical convex lens; the surface of the spherical convex lens is coated with an anti-reflection film targeting the fluorescence wavelength of the target atom.

9. The system according to claim 1, characterized in that, The lens is arranged parallel to the filter, and the effective aperture of the lens is not less than the aperture of the atomic fluorescence emission surface.

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

Images