Method for raman light frequency correlation phase measurement in an atomic gravimeter

Abstract

The application discloses a Raman light frequency correlation phase measurement method in an atomic gravimeter, and comprises the following steps: controlling a signal source to be in an FSK frequency hopping mode, taking a signal at a sync end of the signal source as a trigger, and collecting waveform data of the output signal; determining actual hopping time of the output signal at each frequency by comparing the amplitude change of the residual error of the waveform before and after the hopping; selecting signal data at both ends away from the trigger signal step time corresponding to the frequency hopping of each frequency, fitting the signal data to obtain the phase at the trigger time, then calculating the phase shift difference before and after the frequency hopping of each frequency, and then calculating the additional phase difference value of the frequency chain system under each frequency; and finally calculating the final frequency correlation phase by an interference phase calculation formula. The application can measure the frequency correlation phase in the Raman light frequency chain system in the atomic gravimeter.

Description

Technical Field

[0001] This invention belongs to the field of atomic interferometric gravity measurement, and more specifically, relates to a method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter. Background Technology

[0002] Gravitational acceleration is one of the key physical parameters of the Earth's surface gravitational field, and gravity measurement is of great significance in many fields such as geophysics, fundamental physics research, resource exploration, and gravity navigation. Among them, atomic interferometry gravity measurement is one of the important means to achieve high-precision absolute gravity measurement.

[0003] In actual measurements, to compensate for the Doppler frequency shift caused by the relative motion between atoms and the laser, the laser frequency of the interferometer is linearly scanned within a certain range. Atomic interference fringes containing gravitational information are obtained by changing the laser's sweep rate. During the frequency scanning process, imperfections in the frequency chain may cause a deviation between the phase of the actual output signal and the ideal situation, thus introducing systematic errors into the measurement results.

[0004] Therefore, how to measure the frequency-correlated phase in the Raman optical sweep frequency chain system of an atomic gravimeter is an urgent problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for measuring the frequency-correlated phase of Raman light in an atomic gravimeter, which can measure the frequency-correlated phase in the Raman light sweep frequency chain system of an atomic gravimeter.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter, comprising the following steps:

[0007] (1) The signal source in the sweep frequency chain system of the atomic gravimeter is controlled to be in FSK frequency hopping mode, and the sync terminal signal of the signal source is used as the trigger. The synchronous step signal output by the signal source indicates the jumping time of its output signal, and the waveform data of the output signal is collected at the same time. The signal source continuously outputs frequency signals f1, f2, and f3 in FSK frequency hopping mode, and f2 - f1 = f3 - f2.

[0008] (2) By comparing the waveform data before and after the jump, the amplitude change of the residual is used to determine the actual jump time of the output signal at frequencies f1 and f2; and the signal data at both ends of the trigger signal step time corresponding to the frequency jump at frequencies f1 and f2 are selected respectively, and the phase of the signal data at both ends of the two frequencies at the trigger time is obtained by fitting them, and then the phase shift difference in the output signal before and after the two frequency jumps is calculated.

[0009] (3) Calculate the additional phase difference of the sweep frequency chain system at frequencies f1 and f2 based on the phase shift difference, and then calculate the final frequency-related phase using the interference phase calculation formula.

[0010] The Raman light frequency correlation phase measurement method in the atomic gravimeter provided by the present invention has the following effects: (1) By placing the signal source in FSK frequency hopping mode and analyzing the phase shift difference of the signal source output signal before and after the frequency jump, the additional phase difference value of the frequency chain loop at different frequencies can be obtained, and the final frequency correlation phase can be determined; (2) By comparing the amplitude change of the residual before and after the jump, the actual frequency jump time can be determined, which can eliminate the measurement error introduced by the fluctuation of the frequency jump time during the measurement process, and thus obtain the frequency correlation phase; (3) By selecting the signal data at both ends far from the step time of the trigger signal and obtaining the signal phase difference before and after the frequency jump by fitting, the possible waveform distortion near the frequency jump time can be avoided.

[0011] In one embodiment, in step (3), the additional phase difference value of the sweep frequency chain system at frequency f1 is... The calculation formula is:

[0012]

[0013] Additional phase difference of a swept frequency chain system at frequency f2 The calculation formula is:

[0014]

[0015] The formula for calculating the frequency-dependent phase Δφ is:

[0016]

[0017] In the formula, t0 is the trigger signal step time corresponding to the output signal jumping from frequency f1 to frequency f2; φ1(t0)-φ2(t0) is the phase shift difference of the output signal before and after the frequency f1 jump, and φ1(t0) and φ2(t0) correspond to the phases of the two signal data at frequency f1 at the trigger signal step time t0; τ0 is the time interval between the actual jump time of frequency f1 and the trigger signal step time t0 when the output signal jumps from frequency f1 to frequency f2; t1 is the trigger signal step time corresponding to the output signal jumping from frequency f2 to frequency f3; φ2(t1)-φ3(t1) is the phase shift difference of the output signal before and after the frequency f2 jump, and φ2(t1) and φ3(t1) correspond to the phases of the two signal data at frequency f2 at the trigger signal step time t1; τ1 is the time interval between the actual jump time of frequency f2 and the trigger signal step time t1 when the output signal jumps from frequency f2 to frequency f3.

[0018] In one embodiment, step (2), determining the actual transition time of the output signal at frequencies f1 and f2, specifically involves:

[0019] Select a portion of the signal waveform before the frequency jump at frequency f1; then shift it by an integer multiple of the period to the trigger signal step time t0 corresponding to the waveform data jumping from frequency f1 to frequency f2; then subtract it from the waveform that partially overlaps with the actual jump times of frequency f1 and f2 to obtain the residual signal; finally, determine the actual jump times of frequency f1 and f2 using the amplitude change of the residual signal.

[0020] In one embodiment, the step of determining the actual transition times of frequencies f1 and f2 based on the amplitude change of the residual signal is as follows:

[0021] Using the average value of the residual signal smoothing curve before time t0 as the center, and its standard deviation as the half-width of the interval, the fluctuation interval is plotted above and below the residual data. The residual data is then subjected to moving smoothing. The time coordinate of the first data point after the last intersection of the residual signal smoothing curve and the fluctuation interval is taken as the actual jump time.

[0022] In one embodiment, in step (2), cosine fitting is used to obtain the phase of the two signal data at the trigger time at frequencies f1 and f2.

[0023] In one embodiment, an oscilloscope is used to acquire waveform data of the signal output signal from the signal source.

[0024] Secondly, the present invention provides a gravity measurement method for an atomic gravimeter, including the Raman light frequency correlation phase measurement method in the atomic gravimeter described above. Attached Figure Description

[0025] Figure 1 This is a flowchart of a Raman light frequency correlation phase measurement method in an atomic gravimeter provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of a frequency chain system frequency-addition phase measurement scheme provided in a specific embodiment of the present invention;

[0027] Figure 3 This is a waveform diagram of fitting the portion of a frequency hopping signal before the hopping phase, provided by a specific embodiment of the present invention;

[0028] Figure 4 yes Figure 3 Waveform of the fitted residual;

[0029] Figure 5 yes Figure 4 Plot of harmonic components in the fitted residuals;

[0030] Figure 6 This is a waveform diagram provided by a specific embodiment of the present invention, which uses the standard deviation of the residual signal amplitude before time t0 as the interval width for actual jump time measurement;

[0031] Figure 7 yes Figure 6 A magnified view of a portion of the image. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] This invention provides a method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter, such as... Figure 1 As shown, the measurement method includes steps S10 to S40, which are detailed below:

[0034] S10 controls the signal source in the frequency chain system of the atomic gravimeter to be in FSK frequency hopping mode, and uses the sync signal of the signal source as a trigger. The synchronous step signal output by the signal source indicates the transition time of its output signal, and the waveform data of the output signal is acquired at the same time. In FSK frequency hopping mode, the signal source continuously outputs frequency signals f1, f2, and f3, and the interval between two frequency hopping is equal, that is, f2 - f1 = f3 - f2.

[0035] It should be noted that in a frequency sweep chain system, due to imperfections in the frequency chain, the actual frequency transition time of the signal output by the signal source is often greater than the indicated transition time of that frequency, that is, greater than the step time of the trigger signal corresponding to that frequency.

[0036] S20, determine the actual transition times of the signal source output signal at frequencies f1 and f2, and the phase shift difference of the output signal before and after these two frequency transitions.

[0037] In this embodiment, the actual transition time of the output signal at frequencies f1 and f2 is determined by: taking the waveform data collected in step S10 and comparing the amplitude change of the residual before and after the transition to determine the actual transition time of the output signal at frequencies f1 and f2.

[0038] Specifically, a portion of the signal waveform before the frequency jump of frequency f1 can be selected; then, it can be shifted by an integer multiple of the period to the trigger signal step time t0 corresponding to the waveform data jumping from frequency f1 to frequency f2; then, the residual signal can be obtained by subtracting it from the waveform that partially overlaps with the actual jump times of frequency f1 and f2; finally, the actual jump times of frequency f1 and f2 can be determined by the amplitude change of the residual signal.

[0039] Preferably, the steps of determining the actual jump times of frequencies f1 and f2 based on the amplitude changes of the residual signal in this embodiment can be as follows: taking the average value of the residual signal smoothing curve amplitude before time t0 as the center, using its standard deviation as the half-width of the interval, drawing fluctuation intervals above and below the residual data, performing moving smoothing processing on the residual data, and taking the time coordinate of the first data point after the last intersection of the residual signal smoothing curve and the fluctuation interval as the actual jump time.

[0040] In this embodiment, the interval width is selected to ensure that the amplitude fluctuation of the residual signal before the frequency jump does not exceed this width, effectively reflecting the basic fluctuation level of the amplitude signal. If the maximum fluctuation of the residual signal before time t0 is used as the interval width, although the interval can guarantee that all residual amplitudes before time t0 are included, it will result in an excessively large interval width, leading to an excessively large measured frequency jump time and insensitivity to changes in the residual signal amplitude, resulting in a large measurement error. However, using the standard deviation of the residual signal amplitude before time t0 as the interval width can better reflect the basic fluctuation of the residual signal amplitude, and the appropriate interval width is sensitive to amplitude changes occurring at the frequency jump time, resulting in more accurate measurement of the true frequency jump time.

[0041] In this embodiment, the phase shift difference before and after the frequency jumps f1 and f2 in the output signal is determined as follows: Signal data from both ends of the signal are selected at a time far removed from the trigger signal step time corresponding to the frequency jump, and the phase of the two signal data at the trigger time at that frequency is obtained by fitting the data. Then, the phase shift difference before and after the frequency jump in the output signal is calculated. Specifically, this embodiment can use cosine fitting to determine the phase of the two signal data at the trigger time at that frequency.

[0042] It should be noted that the steps of determining the actual transition time and phase shift difference in this embodiment are independent of each other. Therefore, the execution order of these two steps can be performed simultaneously or sequentially. This embodiment does not impose any restrictions.

[0043] S30: Calculate the additional phase difference of the swept frequency chain system at frequencies f1 and f2 based on the phase shift difference, and then calculate the final frequency-related phase using the interference phase calculation formula.

[0044] In step S30, the additional phase difference value of the sweep frequency chain system at frequency f1 is... The calculation formula is:

[0045]

[0046] Additional phase difference of a swept frequency chain system at frequency f2 The calculation formula is:

[0047]

[0048] The formula for calculating the frequency-dependent phase Δφ is:

[0049]

[0050] In the formula, t0 is the trigger signal step time corresponding to the output signal jumping from frequency f1 to frequency f2; φ1(t0)-φ2(t0) is the phase shift difference of the output signal before and after the frequency f1 jump, and φ1(t0) and φ2(t0) correspond to the phases of the two signal data at frequency f1 at the trigger signal step time t0; τ0 is the time interval between the actual jump time of frequency f1 and the trigger signal step time t0 when the output signal jumps from frequency f1 to frequency f2; t1 is the trigger signal step time corresponding to the output signal jumping from frequency f2 to frequency f3; φ2(t1)-φ3(t1) is the phase shift difference of the output signal before and after the frequency f2 jump, and φ2(t1) and φ3(t1) correspond to the phases of the two signal data at frequency f2 at the trigger signal step time t1; τ1 is the time interval between the actual jump time of frequency f2 and the trigger signal step time t1 when the output signal jumps from frequency f2 to frequency f3.

[0051] The Raman light frequency-related phase measurement method provided in this embodiment has the following effects: (1) By placing the signal source in FSK frequency hopping mode and analyzing the phase shift difference of the signal source output signal before and after the frequency jump, the additional phase difference value of the frequency chain loop at different frequencies can be obtained, and the final frequency-related phase can be determined; (2) By comparing the amplitude change of the residual before and after the jump, the actual frequency jump time can be determined, which can eliminate the measurement error introduced by the fluctuation of the frequency jump time during the measurement process, and thus obtain the frequency-related phase; (3) By selecting the signal data at both ends far from the step time of the trigger signal and obtaining the signal phase difference before and after the frequency jump through fitting, the possible waveform distortion near the frequency jump time can be avoided.

[0052] In addition, the present invention also provides a gravity measurement method for an atomic gravimeter, including the Raman light frequency correlation phase measurement method for an atomic gravimeter provided by the present invention.

[0053] The method for measuring frequency-dependent phase provided by the present invention will be described in detail below with reference to specific embodiments:

[0054] The frequency-added phase in the frequency chain system can be obtained from the interference phase calculation formula. The introduced frequency-dependent phase is Where f1, f2, and f3 are the signal source output frequencies corresponding to the three pulse moments of the laser-atomic interaction. The frequency-correlated phase measurement method provided in this embodiment measures... The difference at different frequencies yields the final frequency-dependent phase Δφ.

[0055] Specific measurement plan as follows: Figure 2 Set the signal source to FSK frequency hopping mode, and the output signal frequency jumps from f1 to f2. Use an oscilloscope to collect the complete process of the frequency jump of the signal. Use the synchronous step signal output by the signal source at the same time to indicate the jump time of the signal, and use it as the acquisition trigger of the oscilloscope.

[0056] By selecting signal data at both ends far from the trigger signal step time t0, cosine fitting is performed on them to obtain the phases φ1(t0) and φ2(t0) of the signal data at the trigger time, which satisfy... Where τ0 is the time interval between the actual frequency jump time of frequency f1 and the trigger signal step time t0. Based on the waveform changes of the signal at the frequency jump time, the actual frequency jump time can be determined by comparing the amplitude changes of the residuals before and after the jump, and then obtained from the above formula. The difference between the two frequencies. Keeping the frequency interval constant, the signal jumps from frequency f2 to f3, and the above steps are repeated. The difference is further subtracted to obtain the result for that frequency range. Introduced frequency-dependent phase.

[0057] like Figure 3 and 4 As shown, for a frequency hopping signal that jumps from frequency f1 to f2, with the trigger time t0 as the zero time, the waveform before the trigger time is fitted. Before the trigger time, the signal waveform and the fitted curve are well coincided. At the jump time, the signal frequency changes, and it no longer coincides with the fitted curve, resulting in an amplitude deviation. This amplitude deviation generated at the jump time is used as a sign that the signal has a frequency jump. The residual data is obtained by subtracting the frequency hopping signal data from the fitted curve. The true frequency jump time is obtained by analyzing the starting time of the large amplitude change in the residual data.

[0058] The experiment revealed that the fitted residual data after averaging filtering exhibited significant octave components, such as... Figure 5 As shown. In order to eliminate the influence of the frequency harmonic component on the residual signal, this embodiment selects a portion of the signal waveform before the transition, shifts it to an integer multiple of the period to the trigger time, and calculates the difference between the waveform that partially overlaps with the transition time. The signal itself is used to replace the fitted curve to eliminate the influence of the frequency harmonic component, thereby obtaining a residual signal with smaller fluctuations.

[0059] This method uses the significant amplitude change in the residual data as a marker of a frequency jump. To specifically utilize this amplitude change to obtain the actual jump time, this embodiment performs a moving average on the shifted residual signal to better reflect its overall amplitude fluctuation. Using the average amplitude of the residual signal smoothing curve before time zero as the center, and its standard deviation as the half-width of the interval, fluctuation intervals are plotted above and below the shifted residual data. The residual data is then subjected to moving average smoothing. The time coordinate of the first data point after the last intersection of the residual signal smoothing curve and the fluctuation interval is taken as the actual jump time. Figure 6 and 7 As shown.

[0060] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter, characterized in that, Includes the following steps: (1) The signal source in the sweep frequency chain system of the atomic gravimeter is controlled to be in FSK frequency hopping mode, and the sync terminal signal of the signal source is used as the trigger. The synchronous step signal output by the signal source indicates the jumping time of its output signal, and the waveform data of the output signal is collected at the same time. The signal source continuously outputs frequency signals f1, f2, and f3 in FSK frequency hopping mode, and f2 - f1 = f3 - f2. (2) By comparing the waveform data before and after the jump, the amplitude change of the residual is used to determine the actual jump time of the output signal at frequencies f1 and f2; and the signal data at both ends that are far away from the trigger signal step time corresponding to the frequency jump at frequencies f1 and f2 are selected respectively, and the phase of the signal data at both ends of these two frequencies at the trigger signal step time is obtained by fitting them, and then the phase shift difference before and after the two frequency jumps in the output signal is calculated. (3) Calculate the additional phase difference of the sweep frequency chain system at frequencies f1 and f2 based on the phase shift difference, and then calculate the final frequency-related phase using the interference phase calculation formula.

2. The method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter according to claim 1, characterized in that, In step (3), the additional phase difference value of the sweep frequency chain system at frequency f1 The calculation formula is: Additional phase difference of a swept frequency chain system at frequency f2 The calculation formula is: The formula for calculating the frequency-dependent phase Δφ is: In the formula, t0 is the trigger signal step time corresponding to the output signal jumping from frequency f1 to frequency f2; φ1(t0)-φ2(t0) is the phase shift difference of the output signal before and after the frequency f1 jump, and φ1(t0) and φ2(t0) correspond to the phases of the two signal data at frequency f1 at the trigger signal step time t0; τ0 is the time interval between the actual jump time of frequency f1 and the trigger signal step time t0 when the output signal jumps from frequency f1 to frequency f2; t1 is the trigger signal step time corresponding to the output signal jumping from frequency f2 to frequency f3; φ2(t1)-φ3(t1) is the phase shift difference of the output signal before and after the frequency f2 jump, and φ2(t1) and φ3(t1) correspond to the phases of the two signal data at frequency f2 at the trigger signal step time t1; τ1 is the time interval between the actual jump time of frequency f2 and the trigger signal step time t1 when the output signal jumps from frequency f2 to frequency f3.

3. The method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter according to claim 1 or 2, characterized in that, In step (2), the specific steps for determining the actual transition times of the output signal at frequencies f1 and f2 are as follows: Select a portion of the signal waveform before the frequency jump at frequency f1; then shift it by an integer multiple of the period to the trigger signal step time t0 corresponding to the waveform data jumping from frequency f1 to frequency f2; then subtract it from the waveform that partially overlaps with the actual jump times of frequency f1 and f2 to obtain the residual signal; finally, determine the actual jump times of frequency f1 and f2 using the amplitude change of the residual signal.

4. The method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter according to claim 3, characterized in that, The specific steps for determining the actual transition times of frequencies f1 and f2 based on the amplitude changes of the residual signal are as follows: Using the average value of the residual signal smoothing curve before time t0 as the center, and its standard deviation as the half-width of the interval, the fluctuation interval is plotted above and below the residual data. The residual data is then subjected to moving smoothing. The time coordinate of the first data point after the last intersection of the residual signal smoothing curve and the fluctuation interval is taken as the actual jump time.

5. The method for measuring the frequency correlation phase of Raman light in an atomic gravimeter according to claim 1, characterized in that, In step (2), cosine fitting is used to obtain the phase of the signal data at both ends at the trigger time at frequencies f1 and f2.

6. The method for measuring the frequency correlation phase of Raman light in an atomic gravimeter according to claim 1, characterized in that, The waveform data of the output signal of the signal source is acquired using an oscilloscope.

7. A gravity measurement method using an atomic gravimeter, characterized in that, The method for measuring the frequency-correlation phase of Raman light in an atomic gravimeter as described in any one of claims 1 to 6.

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