Numerical calculation method for inertial noise of cold atom gravimeter

Abstract

The invention discloses a numerical calculation method for inertial noise of a cold atom gravimeter, which comprises the following steps of: measuring an environment in which the cold atom gravimeter is positioned by using a rotation measuring device, an acceleration measuring device and an inertial measuring device which are fixedly connected with the cold atom gravimeter to obtain a corrected output value of the measuring device, defining a sensor coordinate system, and calculating the inertial noise of the cold atom gravimeter. A reflector coordinate system and a laboratory coordinate system, and finally calculating the phase of the cold atom gravimeter and the inertial noise phase after rotation of the reflector. According to the invention, the environmental adaptability of the cold atom interference measurement equipment can be obviously improved without a stable platform and a vibration isolation device, so that the cold atom interference measurement equipment outputs a correct measurement value in a complex rotation and vibration coexisting measurement environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cold atom interferometric precision measurement, and particularly relates to a numerical calculation method of inertial noise of a cold atom gravimeter. BACKGROUND

[0002] The gravimeter, the gravity gradiometer and the gyroscope based on the cold atom interferometric technology have high measurement precision in a static or quasi-static environment, but in a scene with rotation and large vibration, the performance of the measuring equipment will be significantly reduced. For example, the cold atom interferometric absolute gravimeter can achieve micro-g level measurement precision in a non-rotating and small vibration environment, but in a dynamic environment such as a ship, the precision is only milligal level, and the performance is reduced by 2-3 orders of magnitude.

[0003] Therefore, the current equipment is equipped with additional equipment such as a stable platform or a vibration isolation platform to reduce environmental interference and improve the performance of the equipment, but this will also increase the size and weight of the equipment.

[0004] If the simulation software based on the interaction between light and atoms is used to calculate the influence of external inertial noise on the phase of the atom interferometer, it takes a long time, which cannot meet the requirements of high real-time atomic interference inertial measurement devices such as atomic gyroscopes. SUMMARY

[0005] In view of the above problems in the prior art, the purpose of the present application is to provide a numerical calculation method of inertial noise of a cold atom gravimeter.

[0006] The technical scheme adopted by the present application to solve its technical problems is: a numerical calculation method of inertial noise of a cold atom gravimeter, comprising the following steps:

[0007] S1, using a rotation measuring device, an acceleration measuring device and an inertial measuring device fixed with the cold atom gravimeter to measure the environment in which the cold atom gravimeter is located, to obtain the rotation information and acceleration information felt by the cold atom gravimeter, and to obtain the physical quantity actually affecting the cold atom interference process through mechanical analysis; through the above-mentioned physical quantity, all key parameters such as atomic trajectory, laser pointing, mirror position and mirror direction are converted into inertial space, and the response of the inertial measuring device to the above-mentioned inertial noise can be quickly obtained through computer simulation. The response is deducted from the output value of the cold atom gravimeter measuring device to obtain the corrected output value of the cold atom gravimeter measuring device;

[0008] S2, defining the phase of the cold atom gravimeter as ΔΦ = φ(-T) - 2φ(0) + φ(T), φ(t) = 2π , the Raman light wave vector , represents the distance vector of the atom and the mirror in the cold atom gravimeter.

[0009] The time axis of the cold atom gravimeter is defined with the second beam of Raman light as the 0 time point, the first beam of Raman light as the -T time point, and the third beam of Raman light as the T time point, T being the interference time, The initial time of atom release is defined as t0 S The mirror coordinate system R M The laboratory coordinate system R L The angle between the sensitive axis of the sensor in the cold atom gravimeter and the vertical direction in the laboratory coordinate system R L is The angle between the vectors and is , , where represents the average angular velocity between the 1 / 3 pulses of Raman light, represents the average angular acceleration between the 1 / 3 pulses of Raman light;

[0010] The time axis of the cold atom gravimeter is defined with the second beam of Raman light as the 0 time point, the first beam of Raman light as the -T time point, and the third beam of Raman light as the T time point, T being the interference time, The initial time of atom release is defined as t0 Obviously, since the Raman light wave vector rotates with the sensor coordinate axis, the Raman light wave vector which is determined by the sensor coordinate axis and the mirror coordinate axis together can be described in the laboratory coordinate system R L ;

[0011] When the mirror does not rotate additionally, the Raman light can be written as ;

[0012] The position of the cold atom can be represented as , where the initial release time of the atom is t = -t0-T, and the initial speed of the atom is ;

[0013] S3, if the initial angle of the sensor at this time is , and the initial angular velocity is , then the speed of the atom at the release time is , and ;

[0014] S4, if the influence of the gravitational gradient is not considered, then in the first beam of Raman light coordinate system R , the speed is , represents the photon recoil speed of the atom, is the acceleration in the inertial space felt by the atom;

[0015] The above equation can be written in vector form

[0016] S5, according to step S2 formula ΔΦ = φ(-T) - 2φ(0) + φ(T),

[0017] The above equation can be obtained

[0018]

[0019]

[0020] The above equation can be obtained

[0021] Approximation The above equation can be simplified as

[0022] Neglecting and higher order terms, we have The phase of the inertial noise after the mirror rotation, where is the acceleration phase, is the rotation phase, is the angular acceleration phase, is the rotation higher order phase.

[0023] Further, based on the above four terms of acceleration phase, rotation phase, angular acceleration phase and rotation higher order phase, the inertial phase can be obtained through redundant inertial sensors, and subtracted from the gravimeter.

[0024] Further, if the mirror has a rotation generated by separate control, the coordinate system R M does not coincide with the sensor coordinate system R S , only need to bring in the mirror rotation rotation matrix M MS to obtain the normal direction of the mirror after rotation and the new reflected light direction ; bring in to obtain the new Raman light vector , and re-decompose in the inertial system, that is, the phase of the inertial noise after the mirror rotation can be obtained.

[0025] ​​​​​​​​​​​​​​The beneficial effects of this invention are: using this invention can significantly improve the environmental adaptability of cold atom interferometry equipment under conditions without a stable platform or vibration isolation device, enabling the cold atom interferometry equipment to output correct measurement values ​​in a measurement environment with complex rotation and vibration. Attached Figure Description

[0026] Figure 1 The coordinate system R of the internal sensor of the cold atom gravimeter of this invention. S The coordinate system of the reflecting mirror is R. M Laboratory coordinate system R L A schematic diagram. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings.

[0028] This invention uses a cold atom gravimeter as an example; other measuring instruments based on the cold atom interferometry system can be derived by analogy.

[0029] This invention discloses a numerical calculation method for inertial noise in a cold atom gravimeter. First, a rotation measurement device and an acceleration measurement device fixed to the cold atom gravimeter are used to measure the environment in which the cold atom interferometry measurement device is located, obtaining the rotation and acceleration information sensed by the device. Then, through mechanical analysis, the physical quantities that actually affect the cold atom interferometry process are obtained. Using these physical quantities, key parameters such as atomic trajectory, laser pointing, mirror position, and mirror direction are all converted into inertial space. Computer simulation can quickly obtain the response of the cold atom interferometry inertial measurement device when subjected to the aforementioned inertial noise. Subtracting this response from the output value of the cold atom interferometry measurement device yields the corrected output value.

[0030] Raman wave vector .

[0031] The phase of the interferometer is ΔΦ = φ(-T) - 2φ(0) + φ(T), where ,and This represents the distance vector between the atom and the mirror.

[0032] according to Figure 1 The sensor coordinate system R shown S The coordinate system of the reflecting mirror is R. M Laboratory coordinate system R L Then the vector and The included angle θ S (The angle between the sensor's sensing axis and the vertical direction in the laboratory coordinate system) is , , in denotes the average angular velocity between 1 / 3 pulses, denotes the average angular acceleration between 1 / 3 pulses.

[0033] Obviously, since the Raman light (i.e. rotates with the sensor coordinate axis), while the Raman light (i.e. is determined by the sensor coordinate axis and the mirror coordinate axis).

[0034] The sensor sensitive axis can be described in the laboratory coordinate system .

[0035] When the mirror does not rotate additionally, the Raman light can be written as .

[0036] The atomic position can be expressed as .

[0037] Here, the initial release moment of the atom is t = -t0-T, and the initial speed of the atom is . If the initial angle of the sensor at this time is , and the initial angular velocity is , then the speed of the atom at the release moment is , and , where the influence of the gravity gradient is not considered. Then in the coordinate system of the first Raman pulse , the speed is , and the above formula can be written in vector form .

[0038] According to the foregoing derivation, ΔΦ = φ(-T) - 2φ(0) + φ(T), ,

[0039] , , , , , ,

[0040] It can be obtained that ,

[0041] ,

[0042] , it can be obtained that

[0043] , and an approximation is made , then the above formula can be simplified as ,

[0044] Neglecting and its high-order terms, there are .

[0045] Obviously, the above formula can get four items: is the acceleration phase, is the rotation phase, is the angular acceleration phase, is the rotation high-order phase.

[0046] By the above four items, the inertial phase can be obtained by the redundant inertial sensor, and subtracted from the gravimeter.

[0047] Similarly, if the mirror exists a rotation generated by individual control, the coordinate system R M does not coincide with the sensor coordinate system R S , only need to bring the mirror rotation matrix M MS to obtain the normal direction of the mirror after rotation and the new reflected light direction ; bring to obtain the new Raman light vector , re-decompose in the inertial system, and obtain the inertial noise phase after the mirror rotation.

[0048] The application solves the problem that the cold atom interferometric gravimeter, the gravity gradiometer and the cold atom interferometric gyro are difficult to use the accelerometer output value to realize real-time compensation for the effects caused by additional vibration and rotation when the carrier exists complex motion combined with translation and rotation in actual application, thereby finally leading to the performance decline of the above instruments.

[0049] Those skilled in the art can easily understand that the above description is only a preferred use case of the application, and is not used to limit the application, and any modification, equivalent replacement and improvement made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A numerical calculation method for the inertial noise of a cold atom gravimeter, characterized in that: Includes the following steps: S1. The environment around the cold atom gravimeter is measured using a rotation measurement device, an acceleration measurement device, and an inertial measurement device that are fixed to the cold atom gravimeter. The rotation and acceleration information sensed by the cold atom gravimeter is obtained, and the physical quantities that actually affect the cold atom interference process are obtained through mechanical analysis. The key parameters, including atomic trajectory, laser pointing, mirror position, and mirror direction, are all converted into inertial space through the above physical quantities. The response of the inertial measurement device when subjected to the above inertial noise can be quickly obtained through computer simulation. The corrected output value of the measurement device is obtained by subtracting the response from the output value of the measurement device. S2, define the phase of the cold atom gravimeter as ΔΦ = φ(-T) - 2φ(0) + φ(T), φ(t) = Raman wave vector , This represents the distance vector between the atom and the internal mirror of the cold atom gravimeter; Define the time axis of the cold atom gravimeter, with the second Raman beam as time point 0, the first Raman beam as time point -T, and the third Raman beam as time point T, where T is the interference time. Define the sensor coordinate system R at the initial moment of atom release. S The coordinate system of the reflecting mirror is R. M Laboratory coordinate system R L The sensor sensing axis of the cold atom gravimeter is aligned with the laboratory coordinate system R. L The vertical angle in the middle is Then the vector and The included angle between them is , , ,in This represents the average angular velocity between 1 / 3 pulses of Raman light. This represents the average angular acceleration between 1 / 3 pulses of Raman light; Due to Raman light wave vector Raman light The sensor's sensitive axis is mapped using the laboratory coordinate system R. L describe ; When the mirror does not rotate additionally, the Raman light is written as ; The position of a cold atom is represented as In the formula, the initial release time of the atom is t = -t0 - T, and the initial velocity of the atom is... ; S3, if the initial angle of the sensor is The initial angular velocity is Then the velocity of the atom at the moment of release is ,and ; S4, if the effect of the gravitational gradient is not considered, then in the first Raman pulse coordinate system medium speed , The photon recoil velocity of an atom The acceleration felt by the atom in inertial space; The above equation can be written in vector form. , S5, obtained from the formula in S2 ， ， ， Substituting it in will give us... , Make approximations Then the above formula can be simplified to , Omitted and its higher-order terms, have The inertial noise phase after the mirror rotates is obtained, where... For acceleration phase, - For rotation phase, For angular acceleration phase, To rotate to a higher-order phase.

2. The numerical calculation method for inertial noise of a cold atom gravimeter according to claim 1, characterized in that, Based on the acceleration phase, rotational phase, angular acceleration phase, and higher-order rotational phase, the inertial phase is obtained through redundant inertial sensors and subtracted from the gravimeter.

3. A numerical calculation method for inertial noise of a cold atom gravimeter according to claim 1 or 2, characterized in that, If the mirror has a rotation that is controlled independently, then the coordinate system R M With sensor coordinate system R S They do not overlap; only the mirror needs to be rotated by the rotation matrix M. MS Substituting this into the equation yields the normal direction of the rotated mirror. With the new direction of reflected light ; Substitute Obtain the new Raman light vector The inertial noise phase after the mirror rotates is obtained by re-decomposing it in the inertial frame.

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