Miniaturized atomic beam clock physical system and clock generation method

Abstract

The invention relates to the technical field of atomic frequency standards, in particular to a miniaturized atomic beam clock physical system and a clock generation method. The atomic beam clock physical system comprises an alkali metal atom emission cavity, an alkali metal raw material block, a microcapillary array, a drift cavity, a multi-layer silicon substrate, a laser, an optical fiber type phase modulator, a beam splitter prism, a plurality of reflectors and a signal detector. Compared with a traditional coherent population detection mode based on a bubble chamber, the chip-scale atomic clock has narrower fluorescence spectrum width and higher long-term frequency stability, meanwhile has the chip-scale capability, and has higher competitiveness compared with an existing chip-scale atomic clock based on an air chamber structure.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic frequency standards, and more specifically 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 time and frequency devices with high precision, which use the stable transitions between the fine energy levels of atoms as frequency references. Due to their excellent time reference characteristics, they play an irreplaceable role in navigation, transportation, communication and scientific research. Atomic clocks include microwave atomic clocks and optical atomic clocks. Currently, all commercial atomic clocks are microwave atomic clocks, such as cesium atomic microwave clocks and rubidium atomic microwave clocks. Although microwave atomic clocks have been widely used in some fields, their large installation space is not conducive to their widespread practical application.

[0004] Advances in optical detection of hot atoms in miniaturized vapor cells have enabled the development of low-power, chip-scale atomic devices, including atomic clocks and magnetometers. These miniaturized devices typically exploit coherent population trapping (CPT) resonances in the energy levels of alkali metal atoms, which produce coherent dark states between hyperfine ground states by exciting atoms with two λ configurations. Probing microwave transitions with optical fields 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 schemes, 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. As a result, devices such as chip-scale atomic clocks (CSACs) consume only 120 m W of power and can achieve 10 s on average over 1000 s. -11 However, due to the aging and thermal drift of the buffer gas environment, as well as systemic reasons such as optical frequency shift, the buffer gas has long-term instability factors, causing the performance of the existing CSAC atomic clock 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, it is very necessary to develop miniaturized atomic beam physics systems. Summary of the invention

[0006] Purpose of the Invention

[0007] Based on the above description, the object 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 solution:

[0009] A miniaturized atomic beam clock physics system, comprising: an alkali metal atom emission cavity, an alkali metal raw material block, a microcapillary array, a drift cavity, a multilayer silicon substrate, a laser, an optical fiber 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 chamber;

[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 disposed 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 and irradiates the first light beam to the inner side of the first end of the drift cavity, and guides and irradiates the second light beam to 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 multi-layer 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] The alkali metal atoms are emitted by utilizing a block of alkali metal raw material having a low volatilization temperature;

[0028] The paths of the alkali metal atoms are collimated 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 frequency modulating the laser light;

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

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

[0033] The spontaneous fluorescence of the alkali metal atoms at the second end of the drift cavity is received, and the intrinsic oscillation frequency of the drift cavity is adjusted based on the frequency of the spontaneous fluorescence to match the two frequencies. Furthermore, a wave plate is inserted into the laser optical path to change the polarization of the laser 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 a double beam to irradiate atoms, and performs two CPT actions at the front end and the end of the drift cavity. There is phase interference between the two CPT actions, so when the laser frequency is scanned near the resonance, a Ramsey-CPT spectrum line (ten kHz level) with a narrower line width than the CPT spectrum line (hundreds of kHz level) can be obtained from the fluorescence. The second action area (right end in the figure) is used to collect the Ramsey-CPT spectrum line as a frequency discrimination signal (about 6.834GHz), and the error signal of the Ramsey-CPT is obtained after phase demodulation, which is fed back to the servo control system, and then the frequency of the microwave generator is servo-locked, the modulation frequency of the phase modulator is controlled, the frequency error is greatly reduced, and the stability of the atomic beam clock is improved.

[0037] An alkali metal atom emission cavity, a microcapillary array, a drift cavity and a non-evaporative air pump are etched on a silicon substrate to form a prefabricated atomic beam device structure, so that the atomic vapor generated by internal heating forms a high-flux beam in the drift cavity through the capillary array, and then is bonded and packaged using low-permeability glass under high vacuum conditions to form a complete vacuum-level atomic beam device, and 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; the present invention utilizes efficient atomic beam flux, and has a narrower fluorescence spectrum width and higher long-term frequency stability compared to the traditional bubble chamber-based coherent population detection method, and also has the ability to be chip-based, which can be more competitive than the existing chip-level atomic clock based on the gas chamber structure. 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 A composition structure of an 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 discrimination signal is obtained by subtracting the 6.834 GHz discrimination signal from the original signal.

[0041] Reference numerals:

[0042] 1- Alkali metal atom emission cavity;

[0043] 2-Alkali metal atom block 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 is further described in detail below in conjunction with 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 more comprehensively below with reference to the relevant 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 adopts an atomic beam silicon-based prefabricated structure and a cavity structure formed by ion etching a silicon substrate. In this embodiment, two silicon substrates are used, and the alkali metal atom emission cavity 1 is etched on the left silicon substrate, while the micro capillary array 3 and the cavity required for the drift cavity are etched on the right silicon substrate.

[0064] like Figure 1 and 2As shown, the alkali metal atom emission cavity 1 is located in the left area of ​​the atomic beam generating part, and the cavity structure is composed of a multilayer silicon substrate located in the middle and two upper and lower borosilicate glasses 47 with low permeability as packaging layers, which are used for high-temperature heating to generate high-density alkali metal atomic vapor. Before packaging, it is necessary to fill the metal solid (other components are assembled in place), and then use two 2mm thick borosilicate glasses 47 to seal the alkali metal atom emission cavity 1 up and down in a high vacuum environment. Then use a 1mm thick silicon substrate 46 to bond to the borosilicate glass 47 up and down 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, resulting in 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 completing the sealing operation of the atomic beam device, a few watts of 1064nm laser is used to focus on the alkali metal solid 2 in the alkali metal atom emission cavity 1 to activate the alkali metal atoms. In order to make the atomic beam device have a long enough service life, 5 mg of block solid is encapsulated in the source cavity, and laser heating is performed until stable alkali metal atomic vapor is observed.

[0067] The micro capillary array 2 is composed of 20 capillaries with a diameter of 2 mm, a spacing of 70 μm, and a length of 12 mm etched on the second silicon substrate, and is used to connect the alkali metal atom emission cavity 1 and the drift cavity 4. The alkali metal atomic vapor is collimated after passing through the capillary array to generate an atomic beam in the drift cavity. The flux of the atomic beam is determined by the alkali metal atom density in the alkali metal atom emission cavity 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 are heated by the laser to form a dense diffuse atomic vapor. 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 10 11 After obtaining enough atomic beam density, the experiment of laser pumping atoms can be carried out.

[0069] Downstream of the atomic beam generation part is the vacuum closed cavity part, which is mainly composed of two parts: the drift cavity and the non-evaporable getter placement area inside it. The drift cavity is a rectangular cavity structure with an independent vacuum environment. The drift cavity and the alkali metal atom emission cavity are connected by a microcapillary array, which can also provide differential pumping for the drift cavity and the alkali metal atom emission cavity. The atomic beam emitted from the capillary propagates freely for a distance in the drift cavity to interact with the laser to generate a Ramsey signal.

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

[0071] The drift cavity is also formed by etching in 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 by using an adhesive. The package structure is baked at high vacuum and high temperature for about a day to further reduce the influence of other gases.

[0072] A non-getter evaporant 9 is placed inside the non-getter evaporant tank 5 to provide a source for maintaining a low vacuum for the atomic beam vacuum chamber as a whole. After placing the getter, a 1064nm high-power laser is used to heat and activate the getter, and the heating time is controlled within 10-15 minutes. When the observer sees that the getter emits red, the laser focusing heating can be stopped for subsequent signal detection and clock generation.

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

[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 a plurality of reflector parts. 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 a circularly polarized laser.

[0075] The microwave generator is used to drive the phase modulator. The laser first passes through the electro-optic phase modulator for phase modulation. The modulation frequency of the microwave generator (i.e., phase modulator) is 87 Half of the frequency difference between the two ground state hyperfine energy levels of the Rb atom (about 3.417 GHz) is used to act on 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 and equal amplitudes and opposite phases, which are used for optical pumping of alkali metal atoms.

[0077] The modulated circularly polarized laser is divided into two beams, which act on the atomic beam at both ends of the drift cavity. Specifically, the beam splitter prism 12 is used to divide the laser into two parallel optical paths of equal length, which act on the atomic beam at both ends of the drift cavity to perform Ramsey spectrum interrogation at both ends. The two laser beams are referred to as the first beam and the second beam.

[0078] In this embodiment, the laser emitted by the 795nm laser 10 is phase modulated by the fiber-type electro-optic modulator 11, and then enters the beam splitter prism 12 to be divided into two parallel path lasers of equal length. One of the lasers is reflected by the reflector 13 and acts on the atoms near the rightmost end of the drift cavity, and the other laser acts on the atoms near the leftmost end of the drift cavity after passing through the reflectors 14 and 15, thereby performing two-zone Ramsey spectral 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 (right end in the figure) was collected on the silicon-based photodiode with an efficiency of about 5.9%. At the same time, in order to reduce the influence of the external stray magnetic field 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. The magnetic field shielding layer can greatly 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 conducive to the evaluation 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 energy 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 beam, and the coherent two-color light again 87The Rb atom is coupled to the coherent dark state between the two ground state hyperfine energy levels, and the spontaneous fluorescence of the atom is collected in the second action region. Since there is phase interference between the two CPT actions, when the laser frequency is scanned near the resonance, a Ramsey-CPT line (tens of kHz) with a narrower line width than the CPT line (hundreds of kHz) can be obtained from the fluorescence. The second action region (right end of the figure) is used to collect the Ramsey-CPT line as a frequency discrimination signal (about 6.834GHz), and the error signal of the Ramsey-CPT is obtained after phase demodulation, which is fed back to the servo control system, and then the frequency of the microwave generator is servo-locked to realize the closed-loop operation of the Ramsey-CPT atomic beam clock, greatly reduce the frequency error, and improve 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 Magnitude, used to collect Ramsey signals of alkali metal atoms.

[0083] In all thermal atomic clock devices, the collision frequency shift 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 level of the atomic clock. In the atomic beam device of this embodiment, the collision frequency shift 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 diffusion rate of He in many materials and the shortage of He getter materials, the helium penetration process is usually very slow, so it is challenging to stabilize the He pressure in a passive pump device. In order to minimize the impact of He pressure changes, the present invention removes the helium dissolved in the glass when making the rubidium bubble, and uses helium-resistant glass (aluminosilicate) or dielectric film coating to slow down the subsequent helium penetration into the atomic beam device.

[0085] The spin exchange frequency shift of νHF is generated by the collision with the 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 the optical pumping enters the ground state F = 2, ν HF Frequency shift ≈ 3400Hz 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 of 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 demodulation signal of 6.834 GHz from the original signal. As can be seen from the figure, the line width 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 errors 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 general platform for quantum sensing, which is expected to be applied in the future to inertial sensing using atomic interference, 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, which 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, all of which 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 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, an optical fiber phase modulator, a beam splitter, a plurality of reflectors and a signal detector. The alkali metal raw material block is placed in the alkali metal atom emission chamber; 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 disposed 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 reflector guides the first light beam and irradiates the first light beam to the inner side of the first end of the drift cavity. directing and irradiating the second light beam to 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 a 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 795nm, 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 multi-layer 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 arranged outside the aluminate glass cavity.

9. The atomic beam clock physics system according to claim 7, characterized in that: Also included is a microwave generator for driving 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 used as an alkali metal atom emission cavity and a second cavity used as a drift cavity are formed on a silicon substrate by ion etching, a micro capillary array is formed by etching between the first cavity and the second cavity, an alkali metal raw material block is placed in the first cavity, a non-evaporable getter is placed in the second cavity or at a position adjacent to the second cavity, and packaging 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 materials with 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 frequency modulating the laser light; Splitting the laser light into a first light beam and a second light beam; directing and irradiating the first light beam to a first end of the drift cavity, and directing and irradiating the second light beam to a 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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