Atomic Raman interferometer based on flat-topped beam

Abstract

The invention relates to the field of atomic interference measurement, in particular to an atomic Raman interferometer based on a flat-topped beam. Comprising two Raman interference subsystems arranged in parallel, each of the two Raman interference subsystems comprises an ultrahigh vacuum cavity and a light path system, and the light path system comprises a flat-topped beam shaping module located on one side of the high vacuum cavity and a Raman light Doppler sensitive configuration module located on the other side of the high vacuum cavity; in the flat-topped beam shaping module, the holographic algorithm principle is adopted, the actual size of atoms in an interference area is combined to determine the size of a target flat-topped beam, the initial complex amplitude is precisely constrained, and a final diffraction phase is obtained through iterative optimization. After the Raman light passes through the diffraction phase, the Raman light is shaped into a flat-topped light beam with a target size and uniform intensity distribution at the ultrahigh vacuum cavity, so that the coherence efficiency under the same interference time is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of atomic interferometry, specifically relating to an atomic Raman interferometer based on a flat-top beam. Background Technology

[0002] Atomic Raman interferometry, as a new generation of inertial sensing technology, utilizes the matter wave properties of ultracold atoms to achieve high-precision rotational measurements of parameters such as external displacement, acceleration, and angular velocity. Its core lies in manipulating the momentum state of atoms through a two-photon Raman interference process, constructing an atomic interference loop. During the upward projection of the atomic cluster, it passes through two parallel Raman beams, and the interference is achieved by two Raman laser beams. Taking a traditional three-pulse cold atom gyroscope as an example, three Raman pulses are used to interfere with the atoms; the three pulses are... π / 2 -π-π / 2, pulse widths are τ and 2 respectively. τ τ, the time interval between pulses is T During this process, the atoms undergo beam splitting, trajectory convergence, and merging, ultimately completing a four-pulse interference.

[0003] In traditional implementation schemes, Gaussian Raman laser beams are typically used to perform state preparation, beam splitting, and reflection operations on atoms.

[0004] However, traditional Gaussian intensity laser beams exhibit a characteristic of high intensity at the center and attenuation at the edges in space. When the atomic cluster is large, atoms at different spatial locations experience non-uniform Raman interaction intensities. This drastic difference causes atoms at different locations within the cluster to experience completely different Rabi oscillation processes—while central atoms experience a complete π pulse, edge atoms may only be weakly affected. This significantly reduces the contrast of interference fringes and can induce unpredictable phase distortion, completely destroying the coherence of atomic matter waves. Summary of the Invention

[0005] Purpose of the invention: To address the problems of non-uniform Raman transition probabilities and system noise introduced by the non-uniformity of the laser intensity profile in the traditional Gaussian mode distribution used in existing Raman atomic interferometers when interacting with spatially distributed atomic clusters, and to overcome the incompatibility of traditional flat-top beam generation schemes with high loss rates, complex structural designs, and large sizes for high-precision Raman atomic interferometer measurements, a flat-beam-based atomic Raman interferometer is proposed.

[0006] Technical solution: An atomic Raman interferometer based on a flat-top beam includes: two parallel Raman interferometer subsystems, each of which includes: an ultra-high vacuum cavity and an optical path system. The optical path system includes a flat-top beam shaping module located on one side of the high vacuum cavity and a Raman Doppler sensitive configuration module located on the other side of the high vacuum cavity. The ultra-high vacuum chamber has a cuboid structure and uses an all-quartz chamber as the main body of the vacuum chamber. Its six sides are the first light-transmitting surface, the second light-transmitting surface, the first observation surface, the second observation surface, the detection surface, and the welding surface. The first light-transmitting surface is symmetrical to the second light-transmitting surface, the first observation surface is symmetrical to the second observation surface, and the detection surface is symmetrical to the welding surface. The first and second light-transmitting surfaces are used to transmit Raman light, allowing the Raman light to act on atomic clusters within the ultra-high vacuum cavity; the detection surface is used by the detection equipment to observe the atomic interference process within the ultra-high vacuum cavity in real time; the welding surface is used to bond with vacuum adhesive, thereby connecting with other atomic interference devices. The first light-transmitting surface, the second light-transmitting surface, and the detector surface are all coated with an anti-reflection film inside and outside the quartz cavity, which corresponds to the wavelength of the laser light passing through. The flat-top light shaping module is located on the outside of the first light-transmitting surface and is used to generate a first uniform intensity laser beam that is perpendicularly incident from the first light-transmitting surface. The beam has a circular cross-section and a uniform intensity distribution. The spot size is determined by the size of the freely moving atomic clusters in the ultra-high vacuum cavity, and the diameter is smaller than the shorter side length of the first light-transmitting surface. The Raman Doppler-sensitive configuration module is located on the outer side of the second light-transmitting surface. It is used to generate a second uniform-intensity laser beam. The second uniform-intensity laser beam is completely opposite to and coincides with the first uniform-intensity laser beam, so that the first uniform-intensity laser beam generates Doppler-sensitive main Raman light in the ultra-high vacuum cavity; and the second uniform-intensity laser beam generates Doppler-sensitive secondary Raman light in the ultra-high vacuum cavity. The wave vectors of the main Raman light and the secondary Raman light are opposite, their polarization states are orthogonal, and their spot size and intensity are equal. The optical axes of the first uniform intensity laser beam and the second uniform intensity laser beam coincide, and should be aligned simultaneously with the intersection of the diagonals of the first and second light-transmitting surfaces.

[0007] Furthermore, the flat-top optical shaping module includes a polarization-maintaining fiber, a fixed fiber collimator, and a diffraction phase optical element arranged sequentially. The polarization-maintaining fiber is connected at the front end to the Gaussian light generated by the preceding spatial optical path system, and at the back end to the input end of the fixed fiber collimator to initially generate Gaussian intensity parallel light with a fixed spot size. The Gaussian intensity parallel light then passes through the diffraction phase optical element and is incident through the first light-transmitting surface, thus generating a flat-top beam of uniform intensity in the atomic interference region within the preset ultra-high vacuum cavity.

[0008] Furthermore, the design method for diffractive phase optical elements includes the following steps: Step 1: Determine the parameters of the incident Gaussian light. The specific parameters of the incident Gaussian light are determined based on the size of the parallel light spot output by the fixed fiber collimator, including the wavelength of the incident beam and the amplitude and phase distribution of the Gaussian mode light field. Step 2: Determine the parameters of the flat-top beam required for the atomic interference region. The parameters of the flat-top beam include: beam wavelength, target spot diameter, and flat-top beam energy distribution. Step 3: Determine the initial complex amplitude distribution based on the parameters of the incident Gaussian light and the parameters of the target flat-top beam; Step 4: Based on the distance between the diffraction phase optical element and the center of the high vacuum cavity, construct the forward and reverse transfer functions based on the Fresnel diffraction integral formula. Based on the parameters of the incident Gaussian light and the parameters of the target flat-top beam, construct an iterative model. Substitute the initial complex amplitude distribution into the iterative model for iterative optimization to obtain the final optimized diffraction phase. Step 5: The optimized diffraction phase is fabricated into a diffraction phase optical element using geometric phase optical materials or a spatial light modulator, which can generate a target-size flat-top beam with high energy utilization, high top uniformity, and no speckle.

[0009] Furthermore, in step one, the expression for the Gaussian mode light field distribution is as follows:

[0010] in I 0 represents the maximum light intensity at the center of the beam. r The diameter of the light spot produced by the fixed fiber optic collimator. w ( r ) represents the beam waist radius.

[0011] Furthermore, the definition of the flat-top beam in step two specifically adopts a super-Gaussian beam model with certain taper characteristics, and its light field distribution expression is as follows:

[0012] in G and These are the waist radius and order of the super-Gaussian beam, respectively. G,0 is a constant term, representing the normalized light intensity coefficient.

[0013] Furthermore, the initial complex amplitude distribution in step three is constructed by superimposing random phases on the amplitudes of the aforementioned Gaussian mode light field, in order to enhance convergence and optimize the phase structure.

[0014] Furthermore, the iterative model in step four employs an optimized Gerchberg-Saxton algorithm architecture. Based on the Fresnel diffraction integral formula and angular spectrum theory, under the paraxial approximation, the Huygens wavelet of the spherical wave is replaced by a quadratic surface. The transfer function of the iterative model is defined as:

[0015] in, U ( x , y ) represents the complex amplitude distribution of the target image plane. U 0( x 0, y 0) represents the complex amplitude distribution of the initial plane. Substitute the initial value into the aforementioned initial complex amplitude distribution. λ Represents wavelength, k Represents wave arrow, z This represents the transmission distance, but in practice, it is taken as the distance between the diffraction phase optical element and the atomic interference region, depending on the requirements of the optical system.

[0016] Furthermore, in step four of the iterative model, the holographic image plane in the traditional Gerchberg-Saxton algorithm is appropriately constrained again, assuming that the amplitude of a certain holographic surface result is... g '( x , y The amplitude of a certain holographic surface result is compared with the target amplitude. g ( x , y The difference is expressed as: g = g ( x , y )- g '( x , y Set the constraints to... g ( x , y )+ m g , m The step size is limited to the range [0,1]. A feedback mechanism is introduced for iteration, which improves the accuracy of reconstruction while speeding up the operation.

[0017] Furthermore, in step four of the iterative model, the iteration stopping condition adopts an OR gate judgment method. One of them is to satisfy the maximum limit of the number of iterations. If the limit is satisfied, the iteration stops. Secondly, based on the uniformity of beam quality α Stability βThe beam quality uniformity is judged using a joint evaluation method. α Stability β The definition method is as follows: Beam quality uniformity α It describes the overall uniformity of light intensity:

[0018] W 1 represents the energy in the barrel when the light intensity drops to 50% of the maximum light intensity. W 2 represents the energy in the barrel when the light intensity drops to 90% of the maximum light intensity; Stability β The speckle pattern of a light beam, reflecting the smoothness of the light intensity distribution, is defined as:

[0019] Where in the formula I mean The average light intensity of the flat-topped region. I A Indicates the intensity of the fluctuation; If uniformity α ≥0.8 and stability β If the value is ≤0.1, it is considered that the iteration stopping condition is met, the iteration is stopped, and the diffraction phase that meets the condition is output.

[0020] Furthermore, the Raman Doppler sensitive configuration module includes a λ / 4 waveplate and a 0° reflector arranged sequentially along the transmission direction of the first uniform intensity laser beam.

[0021] Beneficial effects: (1) This invention discloses an atomic Raman interferometer based on a flat-top beam, comprising an ultra-high vacuum cavity, a flat-top beam shaping module, and a Raman Doppler sensitive configuration optical path system. The flat-top beam shaping module employs holographic iteration and geometric phase design principles, shaping the Raman beam into a flat-top beam with uniform cross-sectional intensity distribution. Furthermore, the spot size of the flat-top beam can be arbitrarily designed and generated according to the atomic cluster size. Compared to Gaussian beams, when used to excite atomic energy level transitions, flat-top beams significantly reduce phase errors and atomic wave packet distortion caused by intensity gradients, fundamentally improving the contrast and signal-to-noise ratio of atomic interference fringes, thereby significantly enhancing the core measurement accuracy of the atomic interferometric measurement system.

[0022] (2) This invention provides an atomic Raman interferometer based on a flat-top beam, which features a simplified structure and enhanced stability. Utilizing a holographic iterative algorithm and geometric phase, it integrates beam shaping and phase modulation functions, avoiding the complex multi-stage lens groups (such as aspherical systems), apertures, and alignment structures found in traditional flat-top beam generation schemes. This scheme greatly simplifies the optical path system, reduces the number of optical components and reliance on precision mechanical structure adjustments, effectively reduces the system's sensitivity to external environmental vibrations and temperature changes, and improves the long-term reliability and robustness of the entire atomic interferometer device.

[0023] (3) This invention provides an atomic Raman interferometer based on a flat-top beam, which is compact, efficient, and highly easy to use in engineering. The flat-top beam generated by this method can be directly and efficiently applied to a compact atomic interference region without the need for a lengthy transmission path and complex beam manipulation. This makes the core sensor head structure of the atomic interferometer more compact and lightweight, and also greatly simplifies the system installation, debugging, and maintenance process, effectively promoting the miniaturization and lightweight application of atomic interferometric sensing technology in practical engineering. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the configuration and timing process of a four-pulse Raman interferometer in a real-time example of the present invention; Figure 2 This is a single-path structure design diagram and iterative model schematic diagram of the flat-top Raman beam 1 in an embodiment of the atomic Raman interferometer based on a flat-top beam according to the present invention; Figure 3 This is a flowchart illustrating the design process of the diffraction phase optical element of this invention. Figure 4 This is the final optimized diffraction phase distribution diagram obtained in this embodiment of the invention; Figure 5 This is a three-dimensional intensity distribution diagram of the incident beam and the target flat-top beam of the present invention; Figure 6 This is the intensity distribution diagram of the flat-top beam when the present invention is finally applied to the atomic interference region. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0028] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0030] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0032] To address the issue of traditional Gaussian intensity laser beams disrupting the coherence of atomic matter waves, the applicant employs an optical shaping method, specifically a flat-top beam with a "plateau-like" intensity distribution. The millimeter-level uniform intensity distribution of the flat-top beam ensures the coherent evolution of longitudinally distributed atomic clusters throughout the entire domain.

[0033] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0034] Reference Figure 1 , Figure 2 An atomic Raman interferometer based on a flat-top beam includes two parallel Raman interferometer subsystems forming a four-pulse interferometric configuration. The Raman interferometer subsystem includes an ultra-high vacuum cavity and an optical path system. The optical path system includes a flat-top beam shaping module located on one side of the high vacuum cavity and a Raman Doppler sensitive configuration module located on the other side of the high vacuum cavity.

[0035] After being cooled and trapped in the preceding process, the atoms are thrown upwards, selected, and then enter the interference process. A set of four pairs of backpropagating Raman pulses (π / 2-π-π-π / 2) is used, with time intervals of... T -2 T - T Symmetrically separated, with a total interference duration of 4 T .

[0036] Assuming all atoms are in their ground state before the pulse | g , p ›, applied at the start of the pulse. When a π / 2 pulse is applied at the start of the pulse, the atom has a 50% probability of absorbing the photon momentum. | g , p Atoms undergo beam splitting, with some transitioning to | e , p + k eff ›, another part continues to spread. After free flight time T Afterwards, the applied π pulse causes | g , p ›Atoms in this state become| e , p + k eff ›state,| e , p+ k eff ›Atoms in this state become| g , pIn the › state, momentum transfer within the atom is achieved, and the propagation paths become closer. After propagating for 2T, the trajectories intersect, and the atoms in the two states meet in space, but a π / 2 pulse is not applied at this moment. When the atom propagates to 3... T Then, apply another π pulse, | g , p ›state | e , p+ k eff The atom in the › state undergoes a second momentum exchange, and its path gradually converges here. When the atom is in free flight... T Subsequently, the atoms in the two states meet again, and a π / 2 pulse is applied to realize the internal state change of the atoms in the Mach-Zehnder four-pulse interference process. This configuration not only increases the interference time, but also results in a phase output consisting only of the rotational angular velocity Ω, eliminating the need for decoupling the rotational angular velocity and acceleration.

[0037] The ultra-high vacuum chamber provides an ultra-high vacuum environment for atomic physics operations (cooling, confinement, ejection, coherent state preparation, and interference, etc.), reducing collisions between Rb atoms and the background gas. The leakage rate of this ultra-high vacuum chamber is less than 1 × 10⁻⁶. -12 Pa·m 3 / s, with a vacuum degree better than 5×10 at 20℃. -7 The ultra-high vacuum system employs an all-quartz cavity as its main body, with six surfaces: a first light-transmitting surface, a second light-transmitting surface, a first observation surface, a second observation surface, a detection surface, and a welding surface. The welding surface connects to the other components of the atomic interferometer system, enhancing structural stability and simplifying installation. A 780nm antireflective coating can be deposited on the all-quartz cavity surface, significantly improving light transmittance to 99%, offering superior optical performance compared to traditional metallic materials. Furthermore, an ion pump is installed at the bottom of the device to maintain a high vacuum.

[0038] The interference region of the all-quartz cavity also allows for the realization of various T-structures, making it more flexible than metallic materials. We selected a four-pulse interference configuration with T=55ms, and combined with the atomic cluster size, set the diameter of the target emitted flat-top beam spot to 25mm, with each beam having a Raman power of approximately 70mW.

[0039] In the device structure, based on the above-mentioned selection... TA flat-top beam shaping module and a Raman Doppler sensitive configuration optical path system are installed at different heights. The flat-top beam shaping module and the Raman Doppler sensitive configuration module are used to generate a uniform flat-top Raman beam incident from the first light-transmitting surface. For flat-top Raman beam 1 and flat-top Raman beam 2, the corresponding beam directions and optical path configurations are identical. Two beams with a frequency difference of 6.834 GHz are injected into the Raman collimator and set to the same pre-polarization. The frequencies and wave vectors of the Raman beams F1 and F2 are k1 and k2, respectively. Based on the different wave vector directions, the beams are... k 1(- k 1) and - k 2( k 2) The combined wave vector is defined as + k eff (- k eff This is called the reverse Raman transition.

[0040] Raman light passes through the Raman interference region and passes through twice in succession. λ / 4 waveplate. Two Raman collimators are installed in the experiment. The movement of atoms passes through different Raman windows in sequence and finally through this optical path configuration, so that the atoms in the interference region can feel the Raman light from opposite directions and with completely orthogonal polarization states.

[0041] Flat-top light shaping system, refer to Figures 3-6 This invention provides a shaping method for generating a uniform, flat-top beam of arbitrary target size by producing a geometric phase structure based on GS iterative holography. The specific process includes: S1. Determine the dimensional parameters and modes of the parallel beam spot output by the fiber collimator. S2. Determine the spot size and energy distribution of the target flat-top beam. S3. Determine an initial analytical phase, which is used as the initial phase distribution for the diffraction phase iteration. S4. Based on angular spectrum theory, and using the Fresnel diffraction integral formula and transfer function, construct an iterative model, and substitute the initial diffraction phase distribution into the iterative model for optimization. S5. The optimized diffraction phase distribution is then prepared using geometric phase optical materials or input into a spatial light modulator to generate the target flat-top beam in the atomic interference region.

[0042] The iterative model employs an optimized Gerchberg-Saxton algorithm architecture. Based on the Fresnel diffraction integral formula and angular spectrum theory, under the paraxial approximation, the Huygens wavelet of the spherical wave is replaced by a quadric surface. The transfer function of the iterative model is defined as:

[0043] in, U ( x , y ) represents the complex amplitude distribution of the target image plane.U 0( x 0, y 0) represents the complex amplitude distribution of the initial plane. Substitute the initial value into the aforementioned initial complex amplitude distribution. λ Represents wavelength, k Represents wave arrow, z This represents the transmission distance, but in practice, it is taken as the distance between the diffraction phase optical element and the atomic interference region, depending on the requirements of the optical system.

[0044] The iterative model appropriately constrains the holographic image plane in the traditional Gerchberg-Saxton algorithm, assuming that the amplitude of the holographic surface result in a certain iteration is... g '( x , y The amplitude of a certain holographic surface result is compared with the target amplitude. g ( x , y The difference is expressed as: g = g ( x , y )- g '( x , y Set the constraints to... g ( x , y )+ m g , m The step size is limited to the range [0,1]. A feedback mechanism is introduced for iteration, which improves the accuracy of reconstruction while speeding up the operation.

[0045] The iterative model uses an OR gate method to determine the stopping condition for iteration. One condition is that the maximum number of iterations is satisfied; if this condition is met, the iteration stops. Secondly, based on the uniformity of beam quality α Stability β The beam quality uniformity is judged using a joint evaluation method. α Stability β The definition method is as follows: Beam quality uniformity α It describes the overall uniformity of light intensity:

[0046] W 1 represents the energy in the barrel when the light intensity drops to 50% of the maximum light intensity. W 2 represents the energy in the barrel when the light intensity drops to 90% of the maximum light intensity; Stability βThe speckle pattern of a light beam, reflecting the smoothness of the light intensity distribution, is defined as:

[0047] Where in the formula I mean The average light intensity of the flat-topped region. I A Indicates the intensity of the fluctuation; If uniformity α ≥0.8 and stability β If the value is ≤0.1, it is considered that the iteration stopping condition is met, the iteration is stopped, and the diffraction phase that meets the condition is output.

[0048] Specifically, the parameters of the incident light, combined with the experimental system, include the wavelength of the incident beam. λ =780.24nm, beam waist radius (light intensity drops to 1 / e) 2 (radius) w A circular Gaussian beam with a Gaussian spot size of 1=7.5mm has an energy distribution that satisfies the following:

[0049] The parameters of the target flat-top beam, combined with the experimental system, specifically include the super-Gaussian approximation order. p =9, which determines the steepness of the beam edge, and the radius of the target flat-top beam is R =12mm, and its amplitude distribution function is expressed as:

[0050] in r The constructed coordinate system network is defined as follows: r 2 = x 2 + y 2 .

[0051] The initial diffraction phase is determined based on the above parameters before entering the iteration. To simplify the calculation and improve convergence, a phase with all zero values ​​of the Gaussian intensity distribution is actually used for entering the iteration, that is, the initial diffraction phase is expressed as:

[0052] The desired diffraction phase structure is then calculated by executing an iterative loop. Specifically, the amplitude is continuously replaced by the amplitude of the target flat-top beam in the iterative loop, and this process is repeated at least 200 times, or until the beam quality uniformity is satisfied. α Stability β The desired diffraction phase distribution is obtained through a joint evaluation method.

[0053] Figure 4 The desired diffraction phase distribution is obtained as the output of the iteration. This is then fed into a spatial light modulator or fabricated using a special material like liquid crystal to achieve geometric phase. This is placed behind an fiber collimator to geometrically achieve a flat-top beam with high top homogenization, high energy utilization, and target size matching.

[0054] Figure 5 The comparison between the three-dimensional energy distribution of the initial Gaussian beam and the three-dimensional energy of the flat-top beam entering the Raman interference region clearly shows the difference in intensity distribution.

[0055] Figure 6 For example, the simulation results of the flat-top beam output under limited computing power show some speckle distribution in the light intensity distribution, which affects the homogenization. However, after reasonably optimizing the parameters and increasing the number of iterations, there can be a significant improvement.

[0056] In summary, this invention, through holographic iterative design combined with geometric phase modulation, generates a flat-top beam with highly uniform cross-sectional intensity in the atomic interference region, significantly improving the uniformity and coherence of the Raman light field. Compared to traditional Gaussian beams, this technology fundamentally eliminates atomic wave packet distortion and phase errors caused by intensity gradients, directly improving the measurement accuracy of the atomic interferometry system. Simultaneously, the single-component integration of holographic optical elements replaces the active calibration coupling mechanism of complex multi-lens systems, greatly reducing errors. The compact design allows for flat-top shaping of the optical path in the interference region without long-distance transmission, meeting the miniaturization and lightweight development goals of atomic interferometry. Therefore, this invention has broad prospects.

[0057] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A flat-top beam based atomic Raman interferometer, characterized in that, include: Two parallel Raman interferometer subsystems are provided. Each Raman interferometer subsystem includes an ultra-high vacuum cavity and an optical path system. The optical path system includes a flat-top beam shaping module and a Raman Doppler sensitive configuration module located on both sides of the high vacuum cavity. The ultra-high vacuum chamber has a cuboid structure with six sides: two light-transmitting surfaces, two observation surfaces, a detection surface, and a welding surface. The two light-transmitting surfaces are symmetrical, the two observation surfaces are symmetrical, and the detection surface is symmetrical to the welding surface. Two light-transmitting surfaces are used to transmit Raman light; the detection surface is used by the detection equipment to observe the atomic interference process in the ultra-high vacuum cavity in real time; the welding surface is used for vacuum adhesive bonding. Both the light-transmitting surfaces and the detector surface are coated with anti-reflection films inside and outside the quartz cavity, which correspond to the wavelength of the laser light passing through. The flat-top light shaping module is located on the outside of the first light-transmitting surface and is used to generate a first uniform intensity laser beam that is perpendicularly incident from the first light-transmitting surface. The beam has a circular cross-section and a uniform intensity distribution. The spot size is determined by the size of the freely moving atomic clusters in the ultra-high vacuum cavity, and the diameter is smaller than the shorter side length of the first light-transmitting surface. The Raman Doppler-sensitive configuration module is located on the outer side of the second light-transmitting surface. It is used to generate a second uniform-intensity laser beam. The second uniform-intensity laser beam is completely opposite to and coincides with the first uniform-intensity laser beam, so that the first uniform-intensity laser beam generates Doppler-sensitive main Raman light in the ultra-high vacuum cavity; and the second uniform-intensity laser beam generates Doppler-sensitive secondary Raman light in the ultra-high vacuum cavity. The wave vectors of the main Raman light and the secondary Raman light are opposite, their polarization states are orthogonal, and their spot size and intensity are equal. The optical axes of the two uniform intensity laser beams coincide, and they should be aligned simultaneously with the intersection of the diagonals of the two light-transmitting surfaces.

2. A flat-top beam based atomic Raman interferometer according to claim 1, characterized in that: The flat-top optical shaping module includes a polarization-maintaining fiber, a fixed fiber collimator, and a diffraction phase optical element arranged sequentially. The polarization-maintaining fiber is connected at the front end to the Gaussian light generated by the preceding spatial optical path system, and at the back end to the input end of the fixed fiber collimator to initially generate Gaussian intensity parallel light with a fixed spot size. The Gaussian intensity parallel light then passes through the diffraction phase optical element and is incident through the first light-transmitting surface, thus generating a flat-top beam of uniform intensity in the atomic interference region within the preset ultra-high vacuum cavity.

3. A flat-top beam based atomic Raman interferometer according to claim 2, characterized in that: The design method for diffractive phase optical elements includes the following steps: Step 1: Determine the parameters of the incident Gaussian light. The specific parameters of the incident Gaussian light are determined by the size of the parallel light spot output by the fixed fiber collimator, including the wavelength of the incident beam and the amplitude and phase distribution of the Gaussian mode light field. Step 2: Determine the parameters of the flat-top beam required for the atomic interference region. The parameters of the flat-top beam include: beam wavelength, target spot diameter, and flat-top beam energy distribution. Step 3: Determine the initial complex amplitude distribution based on the parameters of the incident Gaussian light and the parameters of the target flat-top beam; Step 4: Based on the distance between the diffraction phase optical element and the center of the high vacuum cavity, construct the forward and reverse transfer functions based on the Fresnel diffraction integral formula. Based on the parameters of the incident Gaussian light and the parameters of the target flat-top beam, construct an iterative model. Substitute the initial complex amplitude distribution into the iterative model for iterative optimization to obtain the final optimized diffraction phase. Step 5: The optimized diffraction phase is fabricated into a diffraction phase optical element using geometric phase optical materials or a spatial light modulator, which can generate a target-size flat-top beam with high energy utilization, high top uniformity, and no speckle.

4. An atom Raman interferometer based on a flat-top beam according to claim 3, characterized in that, In step one, the expression for the Gaussian mode light field distribution is as follows: in I 0 represents the maximum light intensity at the center of the beam. r The diameter of the light spot produced by the fixed fiber optic collimator. w ( r ) represents the beam waist radius.

5. A flat-top beam based atomic Raman interferometer according to claim 4, characterized in that, Step 2 defines a flat-top beam using a super-Gaussian beam model with a certain taper characteristic. Its light field distribution expression is as follows: wherein G and are the beam waist radius and the order of the super-Gaussian beam, respectively, G,0 is a constant term representing the normalized light intensity coefficient.

6. A flat-top beam based atomic Raman interferometer according to claim 5, wherein, The initial complex amplitude distribution in step three is constructed by superimposing random phases on the amplitudes of the aforementioned Gaussian mode light field, in order to enhance convergence and optimize the phase structure.

7. A flat-top beam based atomic Raman interferometer according to claim 6, characterized in that, Step four of the iterative model employs an optimized Gerchberg-Saxton algorithm architecture. Based on the Fresnel diffraction integral formula and angular spectrum theory, under the paraxial approximation, the Huygens wavelet of the spherical wave is replaced by a quadratic surface. The transfer function of the iterative model is defined as: in, U ( x , y ) represents the complex amplitude distribution of the target image plane. U 0( x 0, y 0) represents the complex amplitude distribution of the initial plane. Substitute the initial value into the aforementioned initial complex amplitude distribution. λ Represents wavelength, k Represents wave arrow, z This represents the transmission distance, but in practice, it is taken as the distance between the diffraction phase optical element and the atomic interference region, depending on the requirements of the optical system.

8. A flat-top beam based atomic Raman interferometer according to claim 7, characterized in that, In step four of the iterative model, the holographic image plane is appropriately constrained again in the traditional Gerchberg-Saxton algorithm. It is assumed that the amplitude of a certain holographic surface result is... g '( x , y The amplitude of a certain holographic surface result is compared with the target amplitude. g ( x , y The difference is expressed as: g = g ( x , y )- g '( x , y Set the constraints to... g ( x , y )+ m g , m The step size is limited to the range [0,1]. A feedback mechanism is introduced for iteration, which improves the accuracy of reconstruction while speeding up the operation.

9. An atomic Raman interferometer based on a flat-top beam according to claim 8, characterized in that, Step four is an iterative model. The iteration stopping condition adopts an OR gate judgment method. One of them is to meet the maximum limit of the number of iterations. If the limit is met, the iteration stops. Secondly, the definition method of the beam quality uniformity α and the smoothness β is as follows: the beam quality uniformity α and the smoothness β are judged in the way of combined evaluation. Beam quality uniformity α The overall uniformity of the light intensity is described: W 1 is the energy in the bucket when the light intensity has dropped to 50% of the maximum light intensity, W 2 indicates the energy in the bucket when the light intensity has dropped to 90% of the maximum light intensity; Stationarity β The stationarity of the intensity distribution of the reaction light is defined as the smoothness of the speckle of the light beam. Where in the formula I mean The average light intensity of the flat-topped region. I A Indicates the intensity of the fluctuation; If the uniformity α ≥ 0.8 and the stationarity β ≤ 0.1, it is considered that the iteration stopping condition is satisfied, the iteration is stopped, and the diffraction phase satisfying the condition is output.

10. A flat-top beam based atomic Raman interferometer according to claim 9, wherein, The Raman Doppler sensitive configuration module includes a λ / 4 waveplate and a 0° reflector arranged sequentially along the transmission direction of the first uniform intensity laser beam.

Images