Wavefront phase shift measuring device and method for atom interferometer

Abstract

The invention relates to an atomic interferometer wavefront phase shift measuring device and method, the atomic interferometer wavefront phase shift measuring device comprises a wavefront measuring module and a vacuum cavity, the wavefront measuring module enables laser to enter the vacuum cavity, an optical element is arranged in the vacuum cavity, the optical element comprises a window plate, a wave plate and a reflector, the window plate is arranged at the incident end of the vacuum cavity, and the wave plate is arranged at the incident end of the vacuum cavity. The wave plate and the reflecting mirror are arranged on the vacuum cavity through the fixing frame and are far away from the window plate, and the phase shift amount is calculated by measuring laser wavefront phase distribution of a full path. According to the invention, errors of air disturbance and parameter adjustment are eliminated, the influence of all optical elements in the laser transmission path of the atom interferometer on the wavefront is directly measured, the reliability of data is improved, error traceability and uncertainty evaluation are realized, and the method is adaptive to a high-precision atom interferometer measurement application scene.

Description

Technical Field

[0001] The present invention relates to the technical field of wavefront phase shift measurement, and in particular to an atom interferometer wavefront phase shift measurement device and method. Background Art

[0002] Currently, the main factor limiting the accuracy of atomic interferometer gravimeters is wavefront phase shift. In an atom interferometer, when laser light passes through the system's vacuum windows, wave plates, mirrors, and other optical components, imperfect processing of these components causes changes in the laser wavefront distribution, which in turn causes atomic interference phase shifts and leads to deviations in the gravity measurement results. Furthermore, when optical components are installed in the system, they can also deform due to factors such as the pressure difference between the inside and outside of the vacuum system, mechanical stress during installation, and changes in ambient temperature, resulting in wavefront phase shifts. This deformation is often difficult to measure directly.

[0003] Generally, by changing the parameters of the atom interferometer system, such as the temperature of the cold atom cluster, the diameter of the Raman laser, and the diameter of the probe light, the atomic interference phase or gravity value is observed to evaluate the influence of the wavefront phase shift. For example, the Paris Observatory in France uses evaporative cooling to change the temperature of the cold atoms within the range of 50nK to 7μK. The laser wavefront distribution is then fitted based on the corresponding gravity measurement results. These methods need to ensure that no other factors are introduced during the measurement process, which is a relatively high requirement (R. Karcher, A. Imanaliev, S. Merlet and F. Pereira Dos Santos, New Journal of Physics 20(2018), 113041). The Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences proposed a device and method for real-time measurement of wavefront distortion. The device uses an external laser light source to measure a vacuum cavity window. The window has reflective films of different wavelengths on the inside and outside. The surface profile test results of the laser light source with different wavelengths are used to finally infer the surface profile of the vacuum window (CN110673224A).

[0004] Existing technologies for wavefront phase shift measurement mostly rely on indirect measurement. The measurement process requires controlling other factors to avoid introducing errors. However, in reality, changes in the cold atom temperature, Raman beam diameter, and probe beam diameter will lead to a decrease in the signal-to-noise ratio of the interference signal. Furthermore, changes in the Coriolis force and two-photon phase shift effect will be introduced, making it difficult to obtain accurate wavefront phase shift results. Direct measurement using an external light source only measures the vacuum window, not the wavefront phase shift of all components in the atom interferometer laser path. This results in a complex and inefficient measurement process. Therefore, a highly efficient and accurate device and method for measuring wavefront phase shift in an atom interferometer is needed. Summary of the Invention

[0005] The purpose of the present invention is to provide an atom interferometer wavefront phase shift measurement device and method.

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] On the one hand, the present invention includes a wavefront measurement module and a vacuum cavity, wherein the wavefront measurement module emits laser light into the vacuum cavity, and optical elements are arranged in the vacuum cavity, wherein the optical elements include a window, a wave plate and a reflector, and the window is arranged at the incident end of the vacuum cavity and is inclined to form an angle with the end face of the vacuum cavity so that only the transmitted light beam can pass through the wave plate and the reflector to form a return light beam and enter the wavefront measurement module, and the wave plate and the reflector are arranged on the vacuum cavity through the fixing frame and away from the window, and the phase shift is calculated by measuring the laser wavefront phase distribution of the entire path.

[0008] Furthermore, the wavefront measurement module includes a laser interferometer or a wavefront analyzer.

[0009] Furthermore, a vacuum maintaining pump is provided on the vacuum chamber.

[0010] Furthermore, the optical elements include windows, wave plates and reflectors.

[0011] Furthermore, the window is sealed and mounted on the end face of the vacuum chamber, with an inclination angle ranging from 5° to 10° with the end face of the vacuum chamber.

[0012] Furthermore, the cavity material of the vacuum chamber is stainless steel, titanium alloy or aluminum alloy.

[0013] Furthermore, the window and wave plate are coated with an anti-reflection film, and the reflector is coated with a reflective film.

[0014] In another aspect, a method for measuring wavefront phase shift of an atomic interferometer gravimeter comprises the following steps:

[0015] Install the wavefront phase shift measurement device and adjust the vacuum cavity posture so that the laser enters the vacuum cavity to achieve full-path wavefront phase shift measurement of the laser;

[0016] Change the vacuum chamber pressure, window flange preload, and vacuum chamber temperature to measure the change in laser wavefront phase shift along the entire path.

[0017] According to the full-path wavefront measurement results, the Zernike polynomials are used for fitting, and combined with the distribution of atomic clusters at a specific moment, the atomic interference phase shift caused by the wavefront phase shift is calculated, that is,

[0018] Δφ WF =∫∫n1(x,y)W(x,y)dxdy-2∫∫n1(x,y)W(x,y)dxdy+∫∫n3(z,y)W(x,y)dxdy

[0019] Corresponding gravity measurement result deviation

[0020] δg=Δφ WF / k eff T 2

[0021] The measurement uncertainty of the wavefront phase shift is evaluated based on the analysis of influencing factors such as vacuum chamber pressure difference, preload force and temperature.

[0022] Furthermore, the adjustment range of the vacuum pressure is 1E-8Pa to atmospheric pressure; the adjustment range of the window flange preload is 2N.m to 0N.m, in steps of 0.5Nm; and the adjustment range of the vacuum chamber temperature is 20°C to 30°C, in steps of 1°C.

[0023] The beneficial effects of the present invention are:

[0024] The present invention is an atom interferometer wavefront phase shift measurement device and method. Compared with the prior art, the present invention has the following technical effects:

[0025] The present invention eliminates errors caused by air disturbances and parameter adjustments, directly measures the influence of all optical elements in the atom interferometer laser transmission path on the wavefront, improves data reliability, realizes error tracing and uncertainty assessment, and is suitable for high-precision atom interferometer measurement application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of an atom interferometer wavefront phase shift measurement device according to the present invention;

[0027] Figure 2 The present invention provides a wavefront measuring device structure based on a wavefront analyzer;

[0028] Figure 3 This is a flow chart of a method for measuring wavefront phase shift using an atom interferometer according to the present invention.

[0029] 1-vacuum chamber; 2-fixed frame; 3-metal flange; 4-ion pump; 5-detection beam; 6-window; 7-wave plate; 8-mirror; 9-laser interferometer; 21-laser light source; 22-spectroscopy element; 23-detection beam; 24-vacuum chamber; 25-wavefront analyzer DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to specific examples. The exemplary embodiments and descriptions of the present invention are intended to explain the present invention but are not intended to limit the present invention.

[0031] like Figure 1 As shown in FIG, the present invention designs a device for measuring wavefront phase shift. Figure 2As shown, a window 6 is mounted on a metal flange 3 and sealed at one end of the vacuum chamber 1. A wave plate 7 and a reflector 8 are mounted on a fixed frame 2, which has a flange structure and can be sealed at the other end of the vacuum chamber 1. The vacuum chamber 1 is maintained in vacuum by an ion pump 4. A laser interferometer 9 can measure changes in the laser wavefront. The detection beam 5 enters the vacuum chamber 1 through the window 6 and passes through the wave plate 7 and the reflector 8, then returns to the laser interferometer 9 along the original path. The transmitted wavefront phase shift of the outgoing beam can be measured. The laser interferometer 9 is used to measure the full-path wavefront phase shift. The laser interferometer 9 and the vacuum chamber 1 can be placed horizontally or vertically, or the laser interferometer can be placed horizontally and the vacuum chamber 1 can be placed vertically, with the optical path deflected between the two by a reflector. The vacuum chamber can be placed on a posture adjustment platform, allowing the detection beam 5 to completely pass through the window 6 and wave plate 7, return along the original path after passing through the reflector 8, and then completely pass through the window 6 and wave plate 7 again before entering the laser interferometer 9 to achieve beam interference measurement.

[0032] The laser interferometer can be used to measure the full path wavefront phase shift distribution of the entire laser transmission path, which is recorded as W(x,y), that is,

[0033] W(x,y)=2W dw (x,y)+2W λ / 4 (x,y)+W m (x,y)

[0034] Where W dw is the wavefront phase shift caused by the window, W λ / 4 is the wavefront phase shift caused by the 1 / 4 wave plate, W m is the wavefront phase shift caused by the reflector.

[0035] By changing the pressure of the vacuum chamber 1, the pressure difference between the inside and outside of the chamber causes the vacuum window 6 to deform. By measuring the full-path wavefront change, the influence of the vacuum chamber pressure on W can be analyzed. By changing the preload force of the metal flange 3 outside the window 6, the vacuum window 6 is deformed. By measuring the full-path wavefront change, the influence of the preload force on W can be analyzed. By changing the temperature of the vacuum chamber 1, the vacuum window 6, wave plate 7, and reflector 8 are deformed. By measuring the full-path wavefront change, the influence of temperature on W can be analyzed.

[0036] The wavefront phase shift test device can be installed in a fixed or adjustable manner; the fixed installation is fixed on an optical platform or other immovable platform through a rigid bracket or a pressure block; the adjustable installation is built on a two-dimensional or multi-dimensional adjustment platform, and the displacement is controlled by a knob or an electronic control device.

[0037] In this embodiment, the pressure of the vacuum chamber was adjusted from 1E-8 Pa to standard atmospheric pressure. The pressure change was monitored using the ion pump current, and the change in the wavefront phase shift along the entire laser path was observed to establish a correlation between the vacuum pressure and the wavefront phase shift. The window installation preload was adjusted from 2 N.m to 0 N.m in 0.5 Nm increments. A torque wrench (with an accuracy of ±2%) was used to apply torque to change the deformation of the window. The installation preload was repeatedly applied, and the change in the wavefront phase shift along the entire laser path was observed to establish a correlation between the preload and the wavefront phase shift. The temperature of the vacuum chamber was adjusted from 20°C to 30°C in 0.1°C increments to change the deformation of the optical components along the laser path. The change in the wavefront phase shift along the entire laser path was observed to establish a correlation between the ambient temperature and the wavefront phase shift.

[0038] According to the full-path wavefront measurement results, the Zernike polynomials are used for fitting, and combined with the distribution of atomic clusters at a specific moment, the atomic interference phase shift caused by the wavefront phase shift is calculated, that is,

[0039] Δφ WF =∫∫n1(x,y)W(x,y)dxdy-2∫∫n1(x,y)W(x,y)dxdy+∫∫n3(z,y)W(x,y)dxdy

[0040] Corresponding gravity measurement result deviation

[0041] δg=Δφ WF / k eff T 2

[0042] The measurement uncertainty of the wavefront phase shift is evaluated based on the analysis of influencing factors such as vacuum chamber pressure difference, preload force and temperature.

[0043] like Figure 2 The figure shows the structure of a wavefront measurement device based on a wavefront analyzer. The laser light source 21 emits an expanded detection beam 23, which is incident on a vacuum cavity 24 after passing through a spectrometer 22. The detection beam 23 completely passes through the windows and wave plates of the vacuum cavity 24, returns to the original path after passing through a reflector, passes through the spectrometer 22, and enters a wavefront analyzer 25, realizing full-path wavefront phase shift measurement.

[0044] The wavefront analyzer 25 can be a Shack-Hartmann wavefront analyzer, a four-wave shearing interferometer wavefront analyzer, etc. The laser light source 1 can be a helium-neon laser, a semiconductor laser, a fiber laser, etc., and the wavelength can be 633nm, 780nm, etc.

[0045] like Figure 3As shown, first install the wavefront measurement device and adjust the optical path to measure the wavefront phase shift of the laser along the entire path when it enters the vacuum cavity. Then, change the pressure of the vacuum cavity, observe the change in the wavefront phase shift of the laser along the entire path, and establish a correlation between the vacuum pressure and the wavefront phase shift. Change the preload force of the window installation to change the deformation of the window, observe the change in the wavefront phase shift of the laser along the entire path, and establish a correlation between the preload force and the wavefront phase shift. Change the temperature of the vacuum cavity to change the deformation of the optical elements on the laser path, observe the change in the wavefront phase shift of the laser along the entire path, and establish a correlation between the ambient temperature and the wavefront phase shift. Finally, analyze the above physical factors and the measurement uncertainty of the wavefront phase shift caused by the measurement to achieve the wavefront phase shift measurement accuracy evaluation of the atom interferometer.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An atom interferometer wavefront phase shift measurement device, characterized in that: The invention comprises a wavefront measurement module and a vacuum chamber. The wavefront measurement module allows the laser to enter the vacuum chamber. Optical elements are arranged in the vacuum chamber. The optical elements include a window, a wave plate and a reflector. The window is arranged at the incident end of the vacuum chamber and is inclined to form an angle with the end face of the vacuum chamber. The wave plate and the reflector are arranged on the vacuum chamber through the fixing frame and away from the window. The phase shift is calculated by measuring the laser wavefront phase distribution along the entire path.

2. The atom interferometer wavefront phase shift measurement device according to claim 1, characterized in that: The wavefront measurement module includes a laser interferometer or a wavefront analyzer.

3. The atom interferometer wavefront phase shift measurement device according to claim 1, characterized in that: The vacuum chamber is provided with a vacuum maintaining pump.

4. The atom interferometer wavefront phase shift measurement device according to claim 1, characterized in that: The optical elements include windows, wave plates and reflecting mirrors.

5. The atom interferometer wavefront phase shift measurement device according to claim 1, characterized in that: The window is sealed and mounted on the end face of the vacuum chamber, with an inclination angle ranging from 5° to 10° with the end face of the vacuum chamber.

6. The atom interferometer wavefront phase shift measurement device according to claim 1, characterized in that: The cavity material of the vacuum cavity is stainless steel, titanium alloy or aluminum alloy.

7. The atom interferometer wavefront phase shift measurement device according to claim 1, characterized in that: The window and wave plate are coated with anti-reflection films, and the reflector is coated with a reflective film.

8. A method for measuring wavefront phase shift of an atomic interferometer gravimeter, characterized in that: Use the following steps: Install the wavefront phase shift measurement device and adjust the vacuum cavity posture so that the laser enters the vacuum cavity to achieve full-path wavefront phase shift measurement of the laser; Change the vacuum chamber pressure, window flange preload, and vacuum chamber temperature to measure the change in laser wavefront phase shift along the entire path. According to the full-path wavefront measurement results, the Zernike polynomials are used for fitting, and combined with the distribution of atomic clusters at a specific moment, the atomic interference phase shift caused by the wavefront phase shift is calculated, that is, Δφ WF =∫∫n1(x,y)W(x,y)dxdy-2∫∫n1(x,y)W(x,y)dxdy+∫∫n3(x,u)W(x,y)dxdy Among them, n i (x,y) represents the distribution of atomic clusters when the i-th laser pulse is applied, W(x,y) represents the laser phase shift distribution introduced by the deformation of the optical element, and corresponds to the deviation of the gravity measurement result. δg=Δφ WF / k eff T 2 Among them, k eff is the effective wave vector of Raman laser, and T represents the free evolution time. The measurement uncertainty of the wavefront phase shift is evaluated based on the analysis of influencing factors such as vacuum chamber pressure difference, preload force and temperature.

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