A dual-optical-path signal counting device and method for a mercury ion microwave clock

Abstract

This invention discloses a dual-optical-path signal counting device for a mercury ion microwave clock, comprising a trapping system containing an ion cloud, two fluorescence collection modules, an amplifier module, a comparator module, a photon counting module, an adder module, and a control module. The ion cloud spontaneously emits fluorescence. The two fluorescence collection modules are symmetrically distributed around the central axis of the ion cloud, synchronously collecting fluorescence to generate a first pulse signal and a second pulse signal. The first and second pulse signals sequentially pass through the amplifier module, comparator module, photon counting module, and adder module to obtain the final count value. This invention also discloses a dual-optical-path signal counting method for a mercury ion microwave clock. This invention achieves a signal-to-noise ratio increase of several times compared to a single-optical-path device by synchronizing the time sampling of the two optical path signal collections.

Description

Technical Field

[0001] This invention relates to the field of atomic clock technology, and more particularly to a dual-optical-path signal counting device for a mercury ion microwave clock, and a dual-optical-path signal counting method for a mercury ion microwave clock, which is suitable for improving the signal-to-noise ratio of mercury ion microwave clock signals. Background Technology

[0002] A mercury ion microwave clock is a high-precision atomic clock that uses the frequency of atomic energy level transitions as a reference. Its core principle is to utilize the quantum transitions of mercury ions to generate a high-precision, high-stability frequency signal. Precise timekeeping is achieved by measuring the frequency of this signal. The high stability and accuracy of atomic clocks play a crucial role in timekeeping and time transmission. By monitoring the frequency ratios between different atomic clocks, fundamental theories of modern physics can be studied, such as verifying general relativity, blackbody radiation, and gravitational field measurements. With the increasing precision of modern communication and navigation systems, the demand for high-performance atomic clocks is becoming increasingly urgent. Conducting research on high-performance mercury ion microwave clocks and related technologies is of great significance to enhancing the capabilities of time and frequency systems and is also an essential requirement for the independent development of next-generation satellite navigation systems.

[0003] The performance of an atomic clock is primarily measured by its accuracy and stability. Accuracy reflects the degree of deviation between the frequency standard output frequency and the internationally defined value. Stability can be calculated using the Allan variance definition, and it is related to the atomic transition linewidth and the signal-to-noise ratio of the signal as follows:

[0004] ;

[0005] Among them stability With signal-to-noise ratio Inversely proportional to the signal-to-noise ratio (SNR) of an atomic clock transition signal, a higher SNR corresponds to a lower stability index, indicating better atomic clock performance. Mercury ion microwave clocks utilize specific electric and magnetic fields and physical systems to create a trapping system for ions. A pump excitation source causes ions to undergo inter-energy level transport, resulting in spontaneous emission of weak fluorescence. This fluorescence is amplified and collected using devices such as photomultiplier tubes to generate an electrical signal. This collected signal is then used by a servo system to lock the mercury ion microwave clock in place. Therefore, trapping mercury ions and collecting and counting their spontaneous emission fluorescence are crucial aspects of a mercury ion microwave clock, and the SNR directly affects its performance.

[0006] The trapping field and physical system structure of a mercury ion microwave clock affect the number of trapped ions. The fluorescence intensity is related to the number of ions and the pumping efficiency. Too many or too few ions will lead to a smaller count value of the fluorescence signal generated by spontaneous emission. When the number of trapped ions in a mercury ion microwave clock reaches the optimal value, its signal-to-noise ratio improvement is limited. Therefore, designing a signal counting device to improve the signal-to-noise ratio of a mercury ion microwave clock is an important step in improving the performance of the mercury ion microwave clock. Summary of the Invention

[0007] The purpose of this invention is to count the fluorescence generated by a mercury ion microwave clock while improving the signal-to-noise ratio, and to provide a dual-optical-path counting device for a mercury ion microwave clock, as well as a dual-optical-path counting method for a mercury ion microwave clock.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A dual-optical-path signal counting device for a mercury ion microwave clock includes a trapping system containing an ion cloud. A first optical-path fluorescence collection module and a second optical-path fluorescence collection module are positioned on opposite sides of the ion trapping system and symmetrically distributed around the central axis of the ion cloud. Fluorescence generated by spontaneous emission from the ion cloud is synchronously collected by the first and second optical-path fluorescence collection modules, generating a first electrical pulse signal and a second electrical pulse signal. The first and second electrical pulse signals are synchronously amplified by an amplifier module, signals below a discrimination threshold are synchronously discarded by a comparator module, and synchronously counted by a photon counting module to obtain a first synchronous photon count signal and a second synchronous photon count signal. The first and second synchronous photon count signals are added by an adder module to obtain the final count value.

[0010] Both the first optical path fluorescence collection module and the second optical path fluorescence collection module include a focusing lens, a filter, and a multiplier tube; the fluorescence is focused into a light spot after passing through the focusing lens, and the light spot is filtered by the filter and then illuminates the input end of the multiplier tube, which converts the focused fluorescence into an electrical pulse signal and outputs it.

[0011] The fluorescence, after being focused by a focusing lens and filtered by a filter to remove stray light, is finally focused onto the collection window of the multiplier tube.

[0012] The focusing lens, filter, and multiplier tube of the first optical path fluorescence collection module and the second optical path fluorescence collection module are all symmetrically distributed around the central axis of the ion cloud.

[0013] The first synchronous photon counting signal and the second synchronous photon counting signal are digital signals, and the adder module is a digital adder module.

[0014] It also includes a control module for setting the discrimination threshold of the comparator module and the counting duration of the photon counting module.

[0015] A dual-optical-path signal counting method for a mercury ion microwave clock, utilizing the aforementioned dual-optical-path signal counting device for a mercury ion microwave clock, includes the following steps:

[0016] Step 1: Adjust the first optical path fluorescence collection module and the second optical path fluorescence collection module to a symmetrical distribution state with respect to the central axis of the ion cloud. After the fluorescence is collected by the first optical path fluorescence collection module and the second optical path fluorescence collection module, a first electrical pulse signal and a second electrical pulse signal with the same intensity are obtained.

[0017] Step 2: By presetting the discrimination threshold of the comparator module and the counting duration of the photon counting module through the control module, the first electrical pulse signal and the second electrical pulse signal are synchronously amplified by the amplifier module in sequence, the comparator module synchronously rejects signals smaller than the discrimination threshold, and the photon counting module performs synchronous counting to obtain the first synchronous photon counting signal and the second synchronous photon counting signal.

[0018] Step 3: The first synchronous photon counting signal and the second synchronous photon counting signal are added together by the adder module to obtain the final count value.

[0019] The ion cloud is a mercury ion cloud.

[0020] The present invention has the following advantages over the prior art:

[0021] 1. The fluorescence emitted by the spontaneous emission of mercury ion cloud is collected by a symmetrical optical path device, which ensures the synchronous sampling of fluorescence by the first optical path fluorescence collection module and the second optical path fluorescence collection module.

[0022] 2. The fluorescence collection device identifies, counts, and accumulates weak atomic transition signals to form digital signals. The first synchronous photon count signal and the second synchronous photon count signal are digital signals. The adder module is a digital adder module, which has lower noise compared to processing analog signals, and can improve the signal-to-noise ratio and optimize the stability of the frequency standard.

[0023] 3. The control module is implemented using FPGA, allowing for flexible implementation of functions;

[0024] 4. It can be used in the field of mercury ion microwave clock signal detection and can be easily extended to other atomic clocks based on fluorescence detection. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the dual-optical-path signal counting device of the present invention;

[0026] Among them, 1-trapping system; 2-focusing lens; 3-filter; 4-multiplier tube; 5-first optical path fluorescence collection module; 6-ion cloud; 7-second optical path fluorescence collection module; 8-amplifier module; 9-comparator module; 10-photon counting module; 11-adder module; 12-control module. Detailed Implementation

[0027] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0028] Example 1:

[0029] A dual-optical-path signal counting device for a mercury ion microwave clock includes a confinement system 1, an ion cloud 6, a fluorescence collection module, an amplifier module 8, a comparator module 9, a photon counting module 10, an adder module 11, and a control module 12; the ion cloud 6 is confined in the confinement system 1, and the ion cloud 6 spontaneously emits fluorescence from the excited state in the system.

[0030] In this embodiment, ion cloud 6 is a mercury ion cloud, and the fluorescence emitted by the spontaneous emission of mercury ions can be collected in all directions of ion cloud 6.

[0031] The fluorescence collection module includes a first optical path fluorescence collection module 5 and a second optical path fluorescence collection module 7. The first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are located on both sides of the trapping system 1 and are symmetrically distributed around the central axis of the ion cloud 6. After synchronously collecting the weak fluorescence emitted by the ion cloud 6, they respectively convert the fluorescence into electrical pulse signals.

[0032] Both the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 include a focusing lens 2, a filter 3, and a multiplier tube 4. The focusing lens 2, the filter 3, and the multiplier tube 4 of the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are symmetrically distributed about the central axis of the ion cloud 6. That is: the focusing lens 2 of the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are symmetrically distributed about the central axis of the ion cloud 6; the filter 3 of the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are symmetrically distributed about the central axis of the ion cloud 6; and the multiplier tube 4 of the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are symmetrically distributed about the central axis of the ion cloud 6.

[0033] The fluorescence generated by the spontaneous emission of mercury ions is focused by focusing lens 2. Using focusing lens 2 to focus the fluorescence can prevent the fluorescence from diverging during propagation and improve the fluorescence collection effect. The focused light spot is filtered by filter 3 and then shines on the input end of multiplier tube 4. Filter 3 is used to filter out stray light in the focused light spot. The size of the light spot matches the size of the input end of multiplier tube 4. That is, after the fluorescence is focused by focusing lens 2 and stray light is filtered out by filter 3, it is finally focused on the collection window surface of multiplier tube 4.

[0034] After receiving the light spot, the multiplier tube 4 converts the fluorescence into photoelectrons, which are then multiplied through multiple stages to form an electrical pulse signal. This electrical pulse signal is output from the output terminal of the multiplier tube 4. The first optical path fluorescence collection module 5 outputs the first electrical pulse signal, and the background noise generated by the first optical path fluorescence collection module 5 is the first background signal. The second optical path fluorescence collection module 7 outputs a second electrical pulse signal, and the background noise generated by the second optical path fluorescence collection module 7 is the second background signal. .

[0035] The output terminals of the multiplier tubes 4 in the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are respectively connected to the input terminals of the amplifier module 8. The first electrical pulse signal and the second electrical pulse signal are synchronously transmitted to the amplifier module 8 for synchronous amplification. The amplifier module 8 amplifies the first electrical pulse signal and the second electrical pulse signal to a voltage level that can be detected by the comparator module 9, and then outputs them synchronously from the output terminal of the amplifier module 8. The output of the amplifier module 8 is the first synchronous amplified electrical pulse signal and the second synchronous amplified electrical pulse signal.

[0036] The output of amplifier module 8 is connected to the input of comparator module 9. Comparator module 9 performs synchronous discrimination on the input first synchronous amplified electrical pulse signal and the second synchronous amplified electrical pulse signal. The first synchronous amplified electrical pulse signal and the second synchronous amplified electrical pulse signal that are higher than the discrimination threshold are retained to obtain the first synchronous comparison electrical pulse signal and the second synchronous comparison electrical pulse signal, which are then synchronously output through the output of comparator module 9.

[0037] In this embodiment, the discrimination threshold is classified as a signal amplitude threshold (typically the voltage magnitude of the signal).

[0038] The output of comparator module 9 is connected to the input of photon counting module 10. The first synchronous comparison electrical pulse signal and the second synchronous comparison electrical pulse signal input to photon counting module 10 are counted at high speed by the clock inside photon counting module 10 to obtain the first synchronous photon counting signal and the second synchronous photon counting signal, and then output from the output of photon counting module 10.

[0039] The output of the photon counting module 10 is connected to the input of the adder module 11. The adder module 11 performs addition calculations on the first synchronous photon counting signal and the second synchronous photon counting signal, and then outputs the final count value from the output of the adder module 11.

[0040] Furthermore, the synchronous photon counting signal output by the photon counting module 10 is a digital signal, and the adder module 11 is a digital signal adder module, thus avoiding the additional noise caused by using analog signals and analog adders.

[0041] The control terminal of the control module 12 is connected to the control terminal of the comparator module 9 and the control terminal of the photon counting module 10, respectively. The control module 12 is used to preset the discrimination threshold of the comparator module 9 and the counting duration of the photon counting module 10. In this example, the control module 12 adopts a control circuit based on FPGA (Field Programmable Gate Array).

[0042] Example 2:

[0043] A dual-optical-path signal counting method for a mercury ion microwave clock, utilizing the dual-optical-path signal counting device for a mercury ion microwave clock described in Example 1, includes the following steps:

[0044] Step 1: Collection of fluorescence

[0045] Ions in ion cloud 6 are continuously pumped out and emit fluorescence. The first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are adjusted to a symmetrical distribution around the central axis of ion cloud 6, synchronizing the sampling of fluorescence signals by these modules. After the fluorescence is collected by the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7, a first electrical pulse signal and a second electrical pulse signal are obtained. The fluorescence generated by ion cloud 6 can be collected simultaneously in all directions, such as... Figure 1 As shown, the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are symmetrically arranged on both sides of the confinement system 1. Fluorescence is incident on the first optical path fluorescence collection module 5, passing sequentially through the focusing lens 2 to form a light spot matching the size of the input end (optical window) of the multiplier tube 4. After being filtered by the filter 3, it is transmitted to the input end of the multiplier tube 4, where the photoelectric effect generates photoelectrons. These photoelectrons undergo multiple electron multiplication stages to form an electrical pulse signal, which is output from the output end of the multiplier tube 4. At the same time, the second optical path fluorescence collection module 7 collects the electrical pulse signal through the same process as the first optical path fluorescence collection module 5. The first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are adjusted to be symmetrically distributed around the central axis of the ion cloud 6, so that the number of the first and second electrical pulse signals remains similar. At this time, the first background signal... With the second background signal They are the same size.

[0046] Step 2, Synchronous Counting Function

[0047] By presetting the discrimination threshold of comparator module 9 and the counting duration of photon counting module 10 through control module 12, the first electrical pulse signal and the second electrical pulse signal are synchronously amplified by amplifier module 8 in sequence, comparator module 9 synchronously discards signals smaller than the discrimination threshold, and photon counting module 10 performs synchronous counting to obtain the first synchronous photon counting signal and the second synchronous photon counting signal; the fluorescence emitted by ion cloud 6 is collected by first optical path fluorescence collection module 5 and second optical path fluorescence collection module 7 and becomes the first electrical pulse signal and the second electrical pulse signal. The first electrical pulse signal and the second electrical pulse signal are respectively output as digital signals by amplifier module, comparator module and photon counting module.

[0048] The output terminals of the multiplier tube 4 in the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 are respectively connected to the amplifier module 8. The amplifier module 8 amplifies the first and second electrical pulse signals into millivolt-level first and second synchronous amplified electrical pulse signals and outputs them synchronously. The output terminal of the amplifier module 8 is connected to the input terminal of the comparator module 9. The first and second synchronous amplified electrical pulse signals are compared with preset voltage thresholds, and noise below or equal to the discrimination threshold is filtered out to obtain the first and second synchronous comparison electrical pulse signals. The output terminal of the comparator module 9 is connected to the input terminal of the photon counting module 10. The first and second synchronous comparison electrical pulse signals are counted at high speed in the photon counting module 10 according to the set counting duration, and the first and second synchronous photon count signals are output. The control terminal of the control module 12 is connected to the control terminal of the comparator module 9 and the control terminal of the photon counting module 10 respectively. The control module 12 presets the voltage threshold of the comparator module 9 and the counting duration of the photon counting module 10. The control module can be implemented using the control circuit of an FPGA, which can further reduce its size.

[0049] Step 3: Processing dual-optical-path count values

[0050] The first and second synchronous photon counting signals are processed by accumulating them using a digital adder. Since the background noise and signal values ​​are acquired at the same time, the signal-to-noise ratio (SNR) of the fluorescence signal is improved. Specifically, the SNR of the frequency standard signals (first and second electrical pulse signals) from the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 is... , The fluorescence signal intensity, To calculate the signal-to-noise ratio (SNR) of a frequency standard, the net signal value at half maximum (FWHM) is generally used, as described above. The formula uses As the net signal value, this invention utilizes the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 to symmetrically sample at the same time, and the combined signal is a linear coherent superposition. The total photon count at half height after merging is Its noise still follows a Poisson distribution, and the total noise is the standard deviation of the total photon count. Since stray light background originates from detector dark noise and vacuum cavity wall fluorescence, detector dark noise can be filtered out by setting a threshold voltage through a control device. The symmetrical arrangement and optical shielding of the first optical path fluorescence collection module 5 and the second optical path fluorescence collection module 7 ensure that the non-signal light illuminating the two detectors is identical and uniform, allowing for... The actual signal-to-noise ratio improvement factor of the frequency standard signal is: The output of the photon counting module 10 is connected to the input of the adder module 11. The first synchronous photon counting signal and the second synchronous photon counting signal are digital signals. The adder module 11 is a digital adder module. The first synchronous photon counting signal and the second synchronous photon counting signal are input to the photon counting module to perform addition operations to obtain the final count value, thus avoiding the additional noise brought by the analog adder.

[0051] Stability (Allan variance) and signal-to-noise ratio of a mercury ion microwave clock The relationship is expressed by the following formula:

[0052] ;

[0053] in, The center frequency of the transition spectral line. The linewidth of the transition spectral line, For the feedback cycle, For the sampling period, This represents the signal-to-noise ratio of the frequency standard signal.

[0054] The stability index is affected by the signal-to-noise ratio. The present invention leverages the fundamental difference between signal deterministic enhancement and noise statistical characteristics, and the sum of the two optical paths (one optical path corresponding to each fluorescence collection module) improves the overall signal-to-noise ratio. This boosting mechanism optimizes the frequency stability of the frequency standard in tandem. This provides a universal optimization solution for precision time and frequency systems.

[0055] This invention is not only applicable to mercury ion microwave clocks, but also to trapping system atomic clocks of other optical detection signal types.

[0056] It should be noted that the embodiments described in this invention are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains can make various modifications or additions to the described embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A dual-optical-path signal counting device for a mercury ion microwave clock, comprising a trapping system (1) in which an ion cloud (6) is trapped, characterized in that, The first optical path fluorescence collection module (5) and the second optical path fluorescence collection module (7) are set on both sides of the confinement system (1) and symmetrically distributed around the central axis of the ion cloud (6). The fluorescence generated by the ion cloud (6) can be collected simultaneously in all directions. The fluorescence generated by the spontaneous emission of the ion cloud (6) is synchronously collected by the first optical path fluorescence collection module (5) and the second optical path fluorescence collection module (7). The noise value and signal value of the two paths are collected at the same time to generate the first electrical pulse signal and the second electrical pulse signal. The number of the first electrical pulse signal and the second electrical pulse signal are kept similar, and the magnitude of the first background signal and the second background signal are equal. The first electrical pulse signal and the second electrical pulse signal are synchronously amplified by the amplifier module (8) in sequence, the comparator module (9) synchronously removes signals smaller than the discrimination threshold, and the photon counting module (10) performs synchronous counting to obtain the first synchronous photon counting signal and the second synchronous photon counting signal. The first synchronous photon counting signal and the second synchronous photon counting signal are added by the adder module (11) to obtain the final count value. Both the first optical path fluorescence collection module (5) and the second optical path fluorescence collection module (7) include a focusing lens (2), a filter (3), and a multiplier tube (4). The fluorescence is focused into a light spot after passing through the focusing lens (2), and the light spot is filtered by the filter (3) and then illuminates the input end of the multiplier tube (4). The multiplier tube (4) converts the focused fluorescence into an electrical pulse signal and outputs it. The focusing lens (2), filter (3) and multiplier tube (4) of the first optical path fluorescence collection module (5) and the second optical path fluorescence collection module (7) are all symmetrically distributed around the central axis of the ion cloud (6).

2. The dual-optical-path signal counting device for a mercury ion microwave clock according to claim 1, characterized in that, The fluorescence is focused by the focusing lens (2) and filtered by the filter (3) to remove stray light, and finally focused on the collection window of the multiplier tube (4).

3. The dual-optical-path signal counting device for a mercury ion microwave clock according to claim 1, characterized in that, The first synchronous photon counting signal and the second synchronous photon counting signal are digital signals, and the adder module (11) is a digital adder module.

4. A dual-optical-path signal counting device for a mercury ion microwave clock according to claim 3, characterized in that, It also includes a control module (12) for setting the discrimination threshold of the comparator module (9) and the counting duration of the photon counting module (10).

5. A dual-optical-path signal counting method for a mercury ion microwave clock, utilizing the dual-optical-path signal counting device for a mercury ion microwave clock as described in claim 4, characterized in that... Includes the following steps: Step 1: Adjust the first optical path fluorescence collection module (5) and the second optical path fluorescence collection module (7) to a state of symmetrical distribution around the central axis of the ion cloud (6). After the fluorescence is collected by the first optical path fluorescence collection module (5) and the second optical path fluorescence collection module (7), the first electrical pulse signal and the second electrical pulse signal are obtained. Step 2: By presetting the discrimination threshold of the comparator module (9) and the counting duration of the photon counting module (10) through the control module (12), the first electrical pulse signal and the second electrical pulse signal are synchronously amplified by the amplifier module (8) in sequence, the comparator module (9) synchronously removes signals smaller than the discrimination threshold, and the photon counting module (10) performs synchronous counting to obtain the first synchronous photon counting signal and the second synchronous photon counting signal; Step 3: The first synchronous photon counting signal and the second synchronous photon counting signal are added together by the adder module (11) to obtain the final count value.

6. A dual-optical-path signal counting method for a mercury ion microwave clock according to claim 5, characterized in that, The ion cloud (6) is a mercury ion cloud.

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