A miniaturized atomic beam clock physics system and clock generation method

Abstract

The present invention relates to the field of atomic frequency standards, and more specifically to a miniaturized atomic beam clock physics system and clock generation method. The atomic beam clock physics system comprises an alkali metal atom emission cavity, an alkali metal raw material block, a microcapillary array, a drift cavity, a multilayer silicon substrate, a laser, a fiber-optic phase modulator, a beam splitter, a plurality of reflectors, and a signal detector. Compared to conventional bubble chamber-based coherent population detection methods, the present invention has a narrower fluorescence spectrum width and higher long-term frequency stability. It also has the capability of being fabricated on a chip, making it more competitive than existing chip-scale atomic clocks based on gas chamber structures.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic frequency standards, and more particularly to a miniaturized atomic beam clock physics system and a clock generation method. Background Art

[0002] Atomic beams have played an important role throughout the history of frequency standards metrology and have been used in commercial frequency standards since the 1960s and as national frequency standards to implement the SI definition of the second.

[0003] Atomic clocks are highly accurate time and frequency devices that use the stable transitions between fine atomic energy levels as their frequency reference. Their excellent time reference properties make them irreplaceable in navigation, transportation, communications, and scientific research. Atomic clocks include microwave and optical atomic clocks. Currently, all commercial atomic clocks are microwave, such as cesium and rubidium microwave clocks. While microwave atomic clocks have been widely used in some fields, their large footprint hinders their widespread practical application.

[0004] With the advancement of optical detection technology for hot atoms in miniaturized vapor cells, the development of low-power, chip-scale atomic devices, including atomic clocks and magnetometers, has become possible. These miniaturized devices usually use coherent population trapping (CPT) resonances in the energy levels of alkali metal atoms to excite atoms with two λ configurations, so that the atoms produce coherent dark states between the hyperfine ground states. Using light fields to detect microwave transitions avoids the need for bulky microwave cavities and provides a compact and low-power solution for detecting atoms and achieving battery-powered operation. In these solutions, a buffer gas is usually added to the microwave cavity to reduce the decoherence effect caused by collisions with the gas chamber walls and to narrow the atomic spectral line width. Therefore, devices such as chip-scale atomic clocks (CSACs) only need to consume 120mW of power and can achieve 10 in an average of 1000s. -11 However, due to the aging and thermal drift of the buffer gas environment, as well as systemic factors such as optical frequency shift, the buffer gas has long-term instability factors, causing the performance of existing CSAC atomic clocks to decline after an average time of 1000s, with a drift rate of about 10 per month. -9 Magnitude.

[0005] Miniaturized atomic beam physics systems offer a way to surpass the long-term stability of existing chip-scale devices while avoiding the complexity and high-power requirements of advanced laser cooling schemes. Therefore, the development of miniaturized atomic beam physics systems is highly desirable. Summary of the Invention

[0006] Purpose of the Invention

[0007] Based on the above description, the purpose of the present invention is to provide a miniaturized atomic beam clock physics system and a clock generation method to solve the above technical problems.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A miniaturized atomic beam clock physics system includes: an alkali metal atom emission cavity, an alkali metal raw material block, a microcapillary array, a drift cavity, a multilayer silicon substrate, a laser, a fiber-type phase modulator, a beam splitter, a plurality of reflectors, and a signal detector.

[0010] The alkali metal raw material block is placed in the alkali metal atom emission cavity;

[0011] The first end of the alkali metal atom emission cavity is used to emit alkali metal atoms, and the first end of the microcapillary array is close to the first end of the alkali metal atom emission cavity;

[0012] The drift chamber is provided at the second end of the microcapillary array;

[0013] The metal atom storage source cavity, microcapillary array and drift cavity are embedded in the multilayer silicon substrate;

[0014] The laser is used to emit laser light of a preset wavelength;

[0015] The optical fiber phase modulator receives the laser and performs frequency modulation on the laser;

[0016] The beam splitter prism is arranged at the light outlet of the optical fiber phase modulator to split the laser into a first light beam and a second light beam;

[0017] The reflector guides the first light beam to illuminate the inner side of the first end of the drift cavity, and guides the second light beam to illuminate the inner side of the second end of the drift cavity.

[0018] The signal detector receives the spontaneous fluorescence at the second end of the drift cavity and adjusts the intrinsic oscillation frequency of the drift cavity based on the frequency of the spontaneous fluorescence.

[0019] In a preferred implementation, the signal detector is disposed at an upper portion of the second end of the drift chamber.

[0020] In another preferred implementation, a non-evaporable getter storage tank is provided in the drift chamber, and a non-evaporable getter is placed in the non-evaporable getter storage tank.

[0021] In another preferred implementation, the microcapillary array is composed of a plurality of horizontally arranged capillaries.

[0022] In another preferred implementation, the laser wavelength emitted by the laser is 795 nm, and the alkali metal is rubidium or cesium.

[0023] In another preferred implementation, the modulation frequency of the frequency modulation performed by the optical fiber phase modulator is 3.417 GHz.

[0024] In another preferred implementation, the multilayer silicon substrate is embedded in an aluminate glass cavity.

[0025] In another preferred implementation, a shielding layer is provided outside the aluminate glass cavity.

[0026] In another aspect, the present invention provides a miniaturized clock generation method, the method comprising:

[0027] Utilizing a low-volatile-temperature alkali metal raw material block to emit alkali metal atoms;

[0028] collimating the path of the alkali metal atoms by a microcapillary array to deliver the alkali metal atoms into the drift chamber;

[0029] Using a laser to emit laser light of a preset wavelength;

[0030] receiving the laser light through a fiber-type phase modulator and performing frequency modulation on the laser light;

[0031] Splitting the laser light into a first beam and a second beam;

[0032] directing the first light beam to illuminate the first end of the drift cavity, and directing the second light beam to illuminate the second end of the drift cavity;

[0033] The device receives spontaneous fluorescence emitted by alkali metal atoms at the second end of the drift cavity, and adjusts the intrinsic oscillation frequency of the drift cavity based on the frequency of the spontaneous fluorescence to match the frequencies of the atoms. Furthermore, a wave plate is inserted into the laser light path to change the polarization of the laser light acting on the atoms.

[0034] Furthermore, the wavelength of the laser, the optical fiber phase modulator and the detector are connected to external instruments through an interface for control and signal display.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention uses dual-beam atomic irradiation, performing two CPT actions at the front and rear ends of the drift cavity. Phase interference exists between the two CPT actions. Therefore, when the laser frequency is swept near resonance, a Ramsey-CPT line (in the tens of kHz range) with a narrower linewidth than the CPT line (in the hundreds of kHz range) can be obtained from the fluorescence. The second action region (right end in the figure) collects the Ramsey-CPT line as a frequency discrimination signal (approximately 6.834 GHz). After phase demodulation, the Ramsey-CPT error signal is obtained and fed back to the servo control system. This signal then servo-locks the microwave generator frequency, controls the modulation frequency of the phase modulator, significantly reduces frequency error, and improves the stability of the atomic beam clock.

[0037] An alkali metal atom emission cavity, a microcapillary array, a drift cavity, and a non-evaporative getter pump are etched on a silicon substrate to form a prefabricated atomic beam device structure. Atomic vapor generated by internal heating forms a high-flux beam in the drift cavity through the capillary array. The device is then bonded and packaged with low-permeability glass under high vacuum conditions to form a complete vacuum-grade atomic beam device. Finally, two parallel laser beams are used for optical pumping, and a silicon-based detector is used to collect the fluorescence signal at the end of the drift cavity. By utilizing efficient atomic beam flux, the present invention has a narrower fluorescence spectrum width and higher long-term frequency stability than traditional bubble chamber-based coherent population detection methods. Furthermore, the device has the ability to be fabricated on a chip, making it more competitive than existing chip-level atomic clocks based on gas chamber structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A miniaturized atomic beam clock physics system is provided in an embodiment of the present invention.

[0039] Figure 2 The composition structure of the atomic beam part in a miniaturized atomic beam clock physics system provided by an embodiment of the present invention;

[0040] Figure 3 The detuned signal relative to the demodulation signal is obtained by subtracting the 6.834 GHz demodulation signal from the original signal.

[0041] Reference numerals:

[0042] 1-Alkali metal atom emission cavity;

[0043] 2-Alkali metal atom bulk solid;

[0044] 3-microcapillary array;

[0045] 4-Drift cavity;

[0046] 5- non-evaporable getter storage tank;

[0047] 6-Multilayer silicon substrate;

[0048] 7-aluminate glass;

[0049] 8-magnetic shielding layer;

[0050] 9- non-evaporable getter;

[0051] 10-795nm laser;

[0052] 11-Fiber-optic phase modulator;

[0053] 12-beam splitter prism;

[0054] 13, 14 and 15 - Reflectors

[0055] 16. Signal Detector

[0056] 17. Microwave generator

[0057] 46-single-layer silicon substrate;

[0058] 47-Thick borate glass. DETAILED DESCRIPTION

[0059] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0060] In order to facilitate understanding of the present application, the present application will be described in more detail below with reference to the accompanying drawings. Figure 1 , Figure 2 As shown, this embodiment provides a miniaturized atomic beam clock physics system.

[0061] The atomic beam clock physics system of this embodiment includes: an alkali metal atom emission cavity 1, a micro capillary array 3, a drift cavity 4, a non-gettering evaporant tank 5, a multilayer silicon substrate 6, a laser, and a signal detector.

[0062] The alkali metal atom emission cavity 1 and the micro capillary array 3 are used to generate an atomic beam.

[0063] The alkali metal atom emission cavity 1 is a prefabricated silicon-based structure using atomic beams, with the cavity structure formed by ion etching of the silicon substrate. In this embodiment, two silicon substrates are used: the alkali metal atom emission cavity 1 is etched on the left silicon substrate, while the microcapillary array 3 and the cavity required for the drift chamber are etched on the right silicon substrate.

[0064] like Figure 1 and 2As shown, the alkali metal atom emission chamber 1 is located in the left area of ​​the atomic beam generation section. The cavity structure consists of a multi-layer silicon substrate in the center and two low-permeability borosilicate glasses 47 at the top and bottom as encapsulation layers, which are used for high-temperature heating to produce high-density alkali metal atomic vapor. Before encapsulation, it is necessary to fill it with solid metal (all other components are assembled in place). Then, two 2mm thick borosilicate glasses 47 are used to seal the alkali metal atom emission chamber 1 in a high vacuum environment. Then, a 1mm thick silicon substrate 46 is bonded to the borosilicate glasses 47 at the top and bottom to prepare for subsequent overall vacuum packaging.

[0065] The internal volume of the alkali metal atom emission cavity 1 is about 32 cm 3 , filled with a block metal solid 2 for generating alkali metal atomic vapor. The block solid has a uniform shape and a suitable size to prevent all the alkali metal block solids in the source cavity from being heated unevenly during internal heating, thereby preventing the generation of unstable atomic vapor.

[0066] The alkali metal atom emission cavity 1 uses internal heating (laser irradiation heating) to heat the alkali metal in the source cavity to obtain sufficient atomic beam intensity, thereby ensuring that the subsequent detector can receive a strong signal. After the atomic beam device is sealed, a few watts of 1064nm laser is focused on the alkali metal solid 2 in the alkali metal atom emission cavity 1 to activate the alkali metal atoms. To ensure the long service life of the atomic beam device, a 5mg block of solid is encapsulated in the source cavity and laser heating is performed until a stable alkali metal atomic vapor is observed.

[0067] The microcapillary array 2 consists of 20 capillaries with a diameter of 2 mm, a spacing of 70 μm, and a length of 12 mm, etched on a second silicon substrate. It is used to connect the alkali metal atom emission chamber 1 and the drift chamber 4. The alkali metal atomic vapor is collimated after passing through the capillary array, generating an atomic beam in the drift chamber. The atomic beam flux is determined by the alkali metal atom density in the alkali metal atom emission chamber 1 and the geometric shape of the capillary array. Micromachining technology can arbitrarily modify the shape of the capillary to control the divergence characteristics of the atomic beam.

[0068] The alkali metal atoms in the source cavity form a dense diffuse atomic vapor after being heated by the laser. After passing through the micro-capillary array, the atomic vapor is collimated into an atomic beam with a small divergence angle. The atomic beam density is between 10 11 After obtaining a sufficient atomic beam density, laser pumping of atoms can be carried out.

[0069] Downstream of the atomic beam generation section lies the vacuum enclosure, consisting primarily of a drift chamber and its internal non-evaporable getter housing. The drift chamber is a rectangular, self-contained cavity with an independent vacuum environment. The drift chamber and alkali metal atom emission chamber are connected by a microcapillary array, which also provides differential pumping for the drift and alkali metal atom emission chambers. The atomic beam emitted from the capillaries propagates freely within the drift chamber for a distance, interacting with the laser to generate a Ramsey signal.

[0070] A non-evaporable getter is provided on the right side of the drift cavity to maintain the vacuum environment in the drift cavity and the source cavity.

[0071] The drift cavity is also etched into a multi-layer silicon substrate. The multi-layer silicon substrate is formed into a sealed cavity structure by anodic bonding. The silicon substrate and the glass layer are sealed and packaged into a vacuum cavity in an ultra-high vacuum chamber using an adhesive. The packaged structure is then baked at high vacuum and high temperature for about a day to further reduce the impact of other gases.

[0072] A non-getter evaporant 9 is placed within the non-getter evaporant tank 5, providing a source for maintaining a low vacuum within the atomic beam vacuum chamber. After the getter is placed, it is heated and activated using a high-power 1064nm laser for 10-15 minutes. When the observer observes a red glow from the getter, the laser focusing and heating can be stopped, allowing subsequent signal detection and clock generation.

[0073] A laser irradiation device and a corresponding detection circuit are arranged on the side of the drift cavity.

[0074] The laser irradiation device includes a miniaturized semiconductor laser 10, a fiber-type phase modulator, a beam splitter prism (or a polarization beam splitter prism used in conjunction with a half-wave plate), and several reflectors. The miniaturized semiconductor laser 10 is used to generate a 795nm laser output with relatively pure polarization, and the laser spot morphology is approximately circular. The output laser is circularly polarized laser light.

[0075] The microwave generator is used to drive the phase modulator. The laser first passes through the electro-optical phase modulator for phase modulation. The modulation frequency of the microwave generator (i.e., phase modulator) is 87 Half the frequency difference between the two ground-state hyperfine levels of the Rb atom (approximately 3.417 GHz) is then applied to the atomic clock system (CPTΛ system) of the present invention using the ±1st-order sideband coherent two-color light of the modulated laser. (Preferably, the upper and lower surfaces of the entire cavity are coated with a reflective film to enhance the intracavity effect.)

[0076] The phase-modulated light wave includes a carrier wave with the original frequency ω and positive and negative first-order sidebands with frequencies ω+Ω and ω-Ω respectively, with equal amplitudes and opposite phases, which are used for optical pumping of alkali metal atoms.

[0077] The modulated circularly polarized laser light is split into two beams, which interact with the atomic beam at either end of the drift cavity. Specifically, the beam splitter prism 12 is used to split the laser light into two parallel beams of equal length, which interact with the atomic beam at either end of the drift cavity to perform Ramsey spectral interrogation at both ends. These two laser beams are referred to herein as the first beam and the second beam.

[0078] In this embodiment, the laser light emitted by the 795nm laser 10 is phase modulated by the fiber-type electro-optical modulator 11, and then enters the beam splitter prism 12 to be divided into two parallel paths of equal length. One of the paths is reflected by the reflector 13 and interacts with the atoms near the rightmost end of the drift cavity. The other path is reflected by the reflector 14 and the reflector 15 and interacts with the atoms near the leftmost end of the drift cavity, thereby performing a two-zone Ramsey spectrum interrogation.

[0079] Each reflector is used to redirect the direction of the laser light path so that the laser light paths of the first light beam and the second light beam are perpendicular to the atomic beam device and irradiate the front end and the rear end of the drift cavity respectively.

[0080] Similar to the laboratory CPT atomic beam clock, using 87 Based on the principle of Rb ground state hyperfine splitting (νHF≈6.835GHz), CPT Ramsey spectrum detection was performed on a 30mm long drift cavity. A silicon-based photodiode was set downstream of the drift cavity, and the fluorescence of the atoms in the second zone (the right end in the figure) was collected on the silicon-based photodiode with an efficiency of approximately 5.9%. At the same time, in order to reduce the influence of external stray magnetic fields on the atomic ground state energy level splitting, a magnetic shielding layer 8 was added to the outer layer of the entire atomic beam system device. This magnetic shielding layer can significantly reduce the influence of the external background magnetic field on the atomic energy level, thereby reducing the high-order Zeeman frequency shift effect of the atomic beam clock system, which is beneficial to the assessment of the long-term stability of the system.

[0081] In the drift cavity near the end of the capillary array, the coherent two-color light will 87 The Rb atoms are coupled to the coherent dark state between the two ground state hyperfine levels, and then the atomic beam enters the drift cavity. At this time, the coherent atomic state undergoes phase-free evolution (decoherence). The atomic beam interacts with the second coherent two-color light, and the coherent two-color light again 87Rb atoms couple to a coherent dark state between two ground-state hyperfine levels, and the spontaneous fluorescence emitted by the atoms is collected in a second region. Due to phase interference between the two CPT interactions, when the laser frequency is swept near resonance, a Ramsey-CPT line (on the order of tens of kHz) with a narrower linewidth than the CPT line (on the order of hundreds of kHz) can be obtained from the fluorescence. The Ramsey-CPT line is collected in the second region (right end of the figure) as a frequency discrimination signal (approximately 6.834 GHz). After phase demodulation, the Ramsey-CPT error signal is generated and fed back to the servo control system, which in turn servo-locks the frequency of the microwave generator, achieving closed-loop operation of the Ramsey-CPT atomic beam clock, significantly reducing frequency error and improving the stability of the atomic beam clock.

[0082] In this embodiment, the signal detector is a silicon-based diode detector, which is located at the end of the drift cavity and has an imaging area of ​​mm. 2 The magnitude is used to collect the Ramsey signal of alkali metal atoms.

[0083] In all thermal atomic clock devices, the frequency shift of collisions between alkali metal atoms, between alkali metal atoms and background gas atoms, and between alkali metal atoms and the gas chamber wall limits the long-term stability of the atomic clock. In the atomic beam device of this embodiment, the frequency shift of collisions limits the required vacuum stability. Common background gases such as H2 and He will cause ν HF At 5HzPa -1 The collision frequency shift is of the order of magnitude, and a pressure stability of 1 mPa is required to achieve 10 -12 frequency stability.

[0084] Due to the high diffusivity of He in many materials and the scarcity of He getter materials, the helium permeation process is typically very slow, making stable He pressure in passive pumping devices challenging. To minimize the impact of He pressure variations, the present invention removes helium dissolved in the glass during the fabrication of the rubidium bubble and uses helium-resistant glass (aluminosilicate) or a dielectric film coating to slow subsequent helium permeation into the atomic beam device.

[0085] The spin exchange frequency shift of νHF is generated by collisions with background Rb atoms along the drift cavity, and the magnitude of the Rb-Rb collision frequency shift depends on the occupancy ratio between the ground state hyperfine levels before CPT detection. Assuming that F = 2 when optically pumped into the ground state, ν HF Frequency shift ≈ 3400 Hz Pa -1 For the proven Rb atomic background pressure ≈ 2×10 -6 Pa, the frequency drift rate caused by helium penetration can be less than 10 -17 / day, the influence on the stability of the atomic beam clock is negligible. Therefore, compared with the method using a gas chamber, the method of the present invention is less affected by He and has higher stability.

[0086] Figure 3 It is the detuned signal relative to the demodulation signal obtained by subtracting the 6.834 GHz demodulation signal from the original signal. As can be seen from the figure, the linewidth of the signal is on the order of 10 kHz.

[0087] The atomic beam clock proposed in this embodiment provides a new solution for realizing low size, weight and power (low-SWaP) atomic clocks. In the future, we will continue to focus on achieving the frequency stability target of this atomic clock, and redesign and use integrated optics and thermal packaging technology to produce fully integrated devices at the size and power scale of existing CSAC. Such devices can achieve sub-μs timing error for a period of time, which will be helpful for low SWaP timing applications. The miniaturized atomic beam device disclosed in the present invention is a universal platform for quantum sensing, which is expected to be applied in the future to inertial sensing using atomic interferometry, electrical measurement using Rydberg spectroscopy, and higher performance compact clocks using optical transitions.

[0088] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms of specific changes without departing from the scope of protection of the invention and the claims. These all fall within the scope of protection of the present invention.

Claims

1. A miniaturized atomic beam clock physics system, characterized in that: The atomic beam clock physics system includes: an alkali metal atom emission cavity, an alkali metal raw material block, a microcapillary array, a drift cavity, a multilayer silicon substrate, a laser, a fiber-type phase modulator, a beam splitter, several reflectors and a signal detector. The alkali metal raw material block is placed in the alkali metal atom emission cavity; The first end of the alkali metal atom emission cavity is used to emit alkali metal atoms, and the first end of the microcapillary array is close to the first end of the alkali metal atom emission cavity; The drift chamber is provided at the second end of the microcapillary array; The metal atom storage source cavity, microcapillary array and drift cavity are embedded in the multilayer silicon substrate; The laser is used to emit laser light of a preset wavelength; The optical fiber phase modulator receives the laser and performs frequency modulation on the laser; The beam splitter prism is arranged at the light outlet of the optical fiber phase modulator to split the laser into a first light beam and a second light beam; The reflecting mirror guides the first light beam and irradiates the first light beam to the inner side of the first end of the drift cavity. directing the second light beam to illuminate the inner side of the second end of the drift cavity, The signal detector receives the spontaneous fluorescence at the second end of the drift cavity and locks the modulation frequency of the phase modulator to the frequency of the spontaneous fluorescence.

2. The atomic beam clock physics system according to claim 1, characterized in that: The signal detector is arranged on the upper part or the side part of the second end of the drift chamber.

3. The atomic beam clock physics system according to claim 1, characterized in that: A non-evaporable getter storage tank is provided in the drift chamber, and non-evaporable getter is placed in the non-evaporable getter storage tank.

4. The atomic beam clock physics system according to claim 1, characterized in that: The microcapillary array is composed of a plurality of horizontally arranged capillaries.

5. The atomic beam clock physics system according to claim 1, characterized in that: The laser wavelength emitted by the laser is 795 nm, and the alkali metal is rubidium or cesium.

6. The atomic beam clock physics system according to claim 1, characterized in that: The modulation frequency of the frequency modulation performed by the optical fiber phase modulator is ±3.417 GHz.

7. The atomic beam clock physics system according to claim 1, characterized in that: The multilayer silicon substrate is embedded in an aluminate glass cavity.

8. The atomic beam clock physics system according to claim 7, characterized in that: A shielding layer is provided outside the aluminate glass cavity.

9. The atomic beam clock physics system according to claim 7, characterized in that: The device further includes a microwave generator configured to drive the phase modulator based on the signal detected by the detector.

10. A miniaturized clock generation method, characterized in that: The method comprises: A first cavity serving as an alkali metal atom emission cavity and a second cavity serving as a drift cavity are formed on a silicon substrate by ion etching. A micro-capillary array is etched between the first cavity and the second cavity. An alkali metal raw material block is placed in the first cavity, and a non-evaporable getter is placed in the second cavity or at a position adjacent to the second cavity. Encapsulation is performed above and below the first cavity and the second cavity, respectively. In the first cavity, alkali metal atoms are emitted from a block of alkali metal raw material having a low volatilization temperature; the paths of the alkali metal atoms are aligned by a microcapillary array to deliver the alkali metal atoms into the drift cavity; Using a laser to emit laser light of a preset wavelength; receiving the laser light through a fiber-type phase modulator and performing frequency modulation on the laser light; Splitting the laser light into a first beam and a second beam; directing the first light beam to illuminate the first end of the drift cavity, and directing the second light beam to illuminate the second end of the drift cavity; The spontaneous fluorescence of the alkali metal atoms at the second end of the drift cavity is received, and the modulation frequency of the phase modulator is adjusted based on the frequency of the spontaneous fluorescence to match the two frequencies.

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