A two-dimensional magneto-optical trap with a flat-top beam

Abstract

The present invention relates to the field of atomic sensing technology, and in particular to a flat-top beam two-dimensional magneto-optical trap, which is used to solve the problem that the light intensity distribution of the elliptical light spot in the major and minor axis directions of the existing two-dimensional magneto-optical trap is Gaussian, resulting in the linear cold atomic beam having large divergence angles at both ends, uneven density distribution in the longitudinal direction (along the beam direction), and wide atomic velocity distribution. The flat-top beam two-dimensional magneto-optical trap includes an ultra-high vacuum cavity, a cooling and trapping laser optical path system, a first group of anti-Helmholtz coil components, and a second group of anti-Helmholtz coil components. The present invention uses a non-spherical optical element in the cooling and trapping laser optical path system, so that the cooling and trapping laser beams are shaped into uniform laser beams with rectangular cross sections, and the light polarization states are consistent on the beam cross sections.

Description

Technical Field

[0001] The invention relates to the technical field of atomic sensing, and in particular to a flat-top beam two-dimensional magneto-optical trap. Background Art

[0002] In the field of cold atom research, the preparation of a large number of low-temperature cold atom sources is a prerequisite for conducting related research. Magneto-optical trap (MOT) is an effective way to prepare cold atom sources. When loading atoms in a magneto-optical trap, if the background vacuum is high, the atomic background vapor pressure is small, the initial loading rate is slow, and the number of atoms reaching equilibrium is relatively small. However, due to the small background collision, the lifetime of the atomic group is long. If the background vacuum is low, the atomic background vapor pressure is large, the loading rate is fast, and the number of atoms reaching equilibrium is large. However, due to the excessively high background collision rate, the lifetime of the atomic group is rapidly shortened. In order to solve the above problems, the researchers proposed a method of combining three-dimensional magneto-optical trap (3D-MOT) and two-dimensional magneto-optical trap (2D-MOT) to achieve large-flux, long-life atomic groups. The specific method is to use a low-vacuum two-dimensional magneto-optical trap (usually ≥10 -6 The atoms are pre-cooled to obtain a high number of cold atoms, and then the pre-cooled atomic group is introduced into the high vacuum 3D-MOT (better than 10 -7 Pa) to obtain cold atomic groups with longer lifetimes.

[0003] The structural features of the two-dimensional magneto-optical trap are that it consists of two pairs of orthogonal laser beams, two pairs of rectangular anti-Helmholtz coils, and a vacuum chamber with light passing through all four sides. When the two pairs of rectangular anti-Helmholtz coils are energized, a two-dimensional quadrupole magnetic field with a zero magnetic field line is generated, in which the cold atoms are trapped around the zero magnetic field line along the long symmetry axis. Therefore, the cooling and trapping of atoms in the two-dimensional magneto-optical trap only occur in two dimensions, and there is no cooling and trapping along the long symmetry axis where atoms can move freely. In order to increase the flux of the cooling atomic beam of the two-dimensional magneto-optical trap, the general approach is to increase the length of the cooling zone. The most commonly used method is to increase the number of prisms and make them cooperate with half-glass slides for light splitting, which becomes multi-stage cooling. Since half-glass slides need to be placed between adjacent prisms, an invalid area without cold atomic beams is formed, making it difficult to reduce the volume of the two-dimensional magneto-optical trap in the axial direction and difficult to miniaturize. In addition, increasing the length of the cooling zone will increase the number of λ / 2 glass plates, λ / 4 glass plates, and polarization beam splitters, causing difficulties in installation and adjustment, and thus making the entire two-dimensional magneto-optical trap more sensitive to vibration and temperature changes in the external environment, greatly reducing the reliability of the system during operation.

[0004] Figure 1It is a planar schematic diagram of the structure of the existing two-dimensional magneto-optical trap three-stage cooling system. For convenience, the figure only shows the optical system layout structure in one direction (z direction), and the optical system layout in the other direction (x direction) is exactly the same. The generated cold atomic beam is distributed along the y direction. The two-dimensional magneto-optical trap three-stage cooling system includes a polarization-maintaining optical fiber 1, a collimating beam expander 2, a λ / 2 glass plate 3, a polarization beam splitter prism 4, a λ / 2 glass plate 5, a polarization beam splitter prism 6, a 45-degree reflector 8, a flange tube 11, a magnetic field coil 10, a magnetic field coil 12, a λ / 4 glass plate 9, a λ / 4 glass plate 7, a λ / 4 glass plate 20, a λ / 4 glass plate 13, a λ / 4 glass plate 15, a λ / 4 glass plate 18, a 0-degree reflector 14, a 0-degree reflector 16, a 0-degree reflector 17 and a vacuum chamber 19. Figure 1 It can be seen that the multi-stage two-dimensional magneto-optical trap has a complex structure, many optical elements, the cold atomic beam is interrupted into three parts in the axial space, and there is a large ineffective area between each cooling stage.

[0005] In order to solve the problems existing in the above two-dimensional magneto-optical trap multi-stage cooling structure, researchers proposed to use optical shaping to change the spot of the cooling beam from a circular one to an elliptical spot with a large aspect ratio (Appl. Phys. B (2012) 109: 61–64) to increase the length of the cooling spot. This method effectively eliminates the problems of too many components, difficult adjustment, and invalid areas between stages in the multi-stage cooling method. Since the number of optical components is significantly reduced, the reliability of the two-dimensional magneto-optical trap is greatly improved. However, similar to the two-dimensional magneto-optical trap multi-stage cooling structure, after using this method, the light intensity distribution in the long and short axis directions of the elliptical spot is still Gaussian distribution, so the linear cold atomic beam has large divergence angles at both ends, uneven density distribution in the longitudinal direction (along the beam direction), and wide atomic velocity distribution. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the existing two-dimensional magneto-optical trap, that is, the elliptical light spot used in the major and minor axis directions has a Gaussian distribution of light intensity, which results in the generated linear cold atomic beam having large divergence angles at both ends, uneven density distribution in the longitudinal direction (along the beam direction) of the atomic beam, and a wide atomic velocity distribution, and to provide a flat-top beam two-dimensional magneto-optical trap.

[0007] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides the following technical solutions:

[0008] A flat-top beam two-dimensional magneto-optical trap comprises an ultra-high vacuum cavity, a cooling and trapping laser optical path system, a first set of anti-Helmholtz coil assemblies and a second set of anti-Helmholtz coil assemblies, and the special features thereof are:

[0009] The ultra-high vacuum cavity is a hexahedral structure, and the first optical window, the second optical window, the third optical window, the fourth optical window and the fifth optical window are respectively arranged on the five surfaces thereof, the first optical window is symmetrical with the second optical window, the third optical window is symmetrical with the fourth optical window, and the symmetric surface of the fifth optical window is provided with a vacuum flange hole for connecting with other cold atom devices;

[0010] The first group of anti-Helmholtz coil components includes a first anti-Helmholtz coil and a second anti-Helmholtz coil respectively arranged outside the first optical window and the second optical window, and the second group of anti-Helmholtz coil components includes a third anti-Helmholtz coil and a fourth anti-Helmholtz coil respectively arranged outside the third optical window and the fourth optical window;

[0011] The cooling trapped laser optical path system is used to generate a first uniform laser beam vertically incident from a first optical window, a second uniform laser beam vertically incident from a second optical window, a third uniform laser beam vertically incident from a third optical window, and a fourth uniform laser beam vertically incident from a fourth optical window, wherein the beam cross-sections of the four uniform laser beams are rectangular, and the beam cross-sections are parallel beams with uniform light intensity distribution, and the spot sizes and light intensities of the four uniform laser beams are equal;

[0012] The optical axis of the first uniform laser beam and the optical axis of the second uniform laser beam coincide with each other, and the optical axis of the third uniform laser beam and the optical axis of the fourth uniform laser beam coincide with each other; the center line of the optical axis of the first uniform laser beam and the center line of the optical axis of the third uniform laser beam intersect and are perpendicular;

[0013] The inner and outer surfaces of the window glass of the first optical window, the second optical window, the third optical window and the fourth optical window are coated with anti-reflection films corresponding to the wavelength of the laser passing through.

[0014] Further, the cooling and trapping laser optical path system includes a light source, a laser collimating beam expander, a first polarizing beam splitter prism, and a first optical path component, a second optical path component, a first reflector, and a second reflector;

[0015] The output end of the light source is connected to the input end of the laser collimator and beam expander through an optical fiber; the output light of the light source is divided into two Gaussian laser beams through the laser collimator and beam expander and the first polarization beam splitter prism;

[0016] A Gaussian laser beam passes through the first optical path component to form a first uniform laser beam, the first uniform laser beam is vertically incident from the first optical window, and is emitted from the second optical window and reflected by the first reflector to form a second uniform laser beam, and the second uniform laser beam is vertically incident from the second optical window;

[0017] Another Gaussian laser beam passes through the second optical path component to form a third uniform laser beam, which is vertically incident on the third optical window, and is reflected by the second reflector after emitting from the fourth optical window to form a fourth uniform laser beam, which is vertically incident on the fourth optical window.

[0018] Furthermore, the first optical path component includes a λ / 2 glass plate, a first beam shaping lens group, and a 45-degree reflector arranged in sequence along the propagation direction of the laser beam; the second optical path component includes a second polarization beam splitter prism, a first λ / 4 glass plate, and a second beam shaping lens group arranged in sequence along the propagation direction of the laser beam.

[0019] Furthermore, the first beam shaping lens group includes a first free-form surface lens and a second free-form surface lens arranged in sequence along the propagation direction of the laser beam; the second beam shaping lens group includes a third free-form surface lens and a fourth free-form surface lens arranged in sequence along the propagation direction of the laser beam; the first beam shaping lens group and the second beam shaping lens group are used to shape a Gaussian laser beam with a Gaussian cross-sectional intensity distribution into a uniform intensity laser beam with a uniform intensity distribution on the beam cross section.

[0020] Furthermore, the λ / 2 glass plate and the first λ / 4 glass plate are both mounted in a mounting base that can rotate around its geometric center to adjust the polarization of the laser beam.

[0021] Further, the cooling and trapping laser optical path system includes a light source, a first strip-shaped laser collimating beam expander disposed on the first anti-Helmholtz coil, a second strip-shaped laser collimating beam expander disposed on the third anti-Helmholtz coil, and a first reflector and a second reflector;

[0022] The output end of the light source is connected to the input end of the first strip-shaped laser collimation beam expander and the input end of the second strip-shaped laser collimation beam expander respectively through optical fibers;

[0023] The outgoing light of the light source passes through the first strip laser collimating beam expander to form a first uniform laser beam, the first uniform laser beam is vertically incident from the first optical window, and after being emitted from the second optical window, it is reflected by the first reflector to form a second uniform laser beam, and the second uniform laser beam is vertically incident from the second optical window;

[0024] The outgoing light of the light source passes through the second strip laser collimating beam expander to form a second uniform laser beam, which is vertically incident on the third optical window, and is reflected by the second reflector after being emitted from the fourth optical window to form a fourth uniform laser beam, which is vertically incident on the fourth optical window.

[0025] Furthermore, the first strip-shaped laser collimating beam expander and the second strip-shaped laser collimating beam expander have the same structure and both include a metal shell, in which a third polarization beam splitter prism, a second λ / 4 glass plate, a fifth free-form surface lens, and a sixth free-form surface lens are sequentially arranged along the propagation direction of the outgoing light from the light source.

[0026] Furthermore, the first reflector includes a third λ / 4 glass slide and a first 0-degree reflector sequentially arranged along the propagation direction of the first uniform laser beam; the second reflector includes a fourth λ / 4 glass slide and a second 0-degree reflector sequentially arranged along the propagation direction of the third uniform laser beam.

[0027] Furthermore, the first anti-Helmholtz coil, the second anti-Helmholtz coil, the third anti-Helmholtz coil and the fourth anti-Helmholtz coil have the same structure and all include an annular metal frame; an annular groove is provided on the outer wall of the annular metal frame, and a copper enameled wire is wound in the annular groove; a rectangular through groove is provided on the side wall of the annular metal frame along the axial direction, the rectangular through groove is located on the symmetrical plane of the annular metal frame along the axial direction, and a non-metallic non-conductive material with a matching shape is provided in the rectangular through groove.

[0028] Furthermore, the third λ / 4 glass slide and the fourth λ / 4 glass slide are both formed by splicing a plurality of square λ / 4 glass slides, and when splicing, the fast axes and slow axes of the plurality of square λ / 4 glass slides are installed in the same direction.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention discloses a flat-top beam two-dimensional magneto-optical trap, comprising an ultra-high vacuum cavity, a cooling and trapping laser optical path system, a first group of anti-Helmholtz coil assemblies, and a second group of anti-Helmholtz coil assemblies. The present invention adopts a non-spherical optical element in the cooling and trapping laser optical path system, so that the cooling and trapping laser beams are shaped into uniform laser beams with rectangular cross sections, and the light polarization states are consistent on the beam cross sections. The rectangular uniform light spot fully utilizes the overlapping volume of four uniform laser beams, eliminates the invalid space existing in the multi-stage cooling method of the two-dimensional magneto-optical trap, and increases the effective length of the cooling zone. The linear cold atom beam generated by the present invention has the same density along the axial direction, and the temperature and velocity distribution of the linear cold atoms are relatively consistent, which solves the problem that the elliptical light spot used in the existing two-dimensional magneto-optical trap has a Gaussian distribution of light intensity in the major and minor axis directions, resulting in the linear cold atom beam having large divergence angles at both ends, uneven density distribution in the longitudinal direction (along the beam direction), and wide atomic velocity distribution.

[0031] (2) The cooling and trapping laser optical path system in the flat-top beam two-dimensional magneto-optical trap of the present invention uses only one optical fiber to introduce the laser beam, which reduces the complexity of the cooling and trapping laser optical path system and greatly reduces the number of optical elements in the two-dimensional magneto-optical trap. It also reduces the sensitivity of the two-dimensional magneto-optical trap to external environmental vibrations and temperature changes, and greatly improves the reliability of the two-dimensional magneto-optical trap.

[0032] (3) The flat-top beam two-dimensional magneto-optical trap of the present invention has a compact structure, is easy to install and adjust, and is easy to miniaturize. When used as an atomic source for equipment such as an atomic interferometer and an atomic interferometer gyroscope, it can effectively reduce the volume of the instrument system, improve the portability of the instrument, and is conducive to the engineering application of the instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The schematic diagram is a structural diagram of an existing two-dimensional magneto-optical trap three-stage cooling system structure.

[0034] Figure 1 The reference numerals are as follows: 1-polarization-maintaining optical fiber; 2-collimating beam expander; 3-λ / 2 glass slide; 4-polarization beam splitter; 5-λ / 2 glass slide; 6-polarization beam splitter; 7-λ / 4 glass slide; 8-45 degree reflector; 9-λ / 4 glass slide; 10-magnetic field coil; 11-flange tube; 12-magnetic field coil; 13-λ / 4 glass slide; 14-0 degree reflector; 15-λ / 4 glass slide; 16-0 degree reflector; 17-0 degree reflector; 18-λ / 4 glass slide; 19-vacuum chamber; 20-λ / 4 glass slide.

[0035] Figure 2 It is a structural schematic diagram of a flat-top beam two-dimensional magneto-optical trap embodiment 1 of the present invention;

[0036] Figure 3 for Figure 2 The main view;

[0037] Figure 4 Schematic diagram of light intensity distribution along the Y-axis direction of the cross section of the uniform laser beam generated by the cooling trapping laser optical path system in Example 1 of the present invention;

[0038] Figure 5 is a schematic structural diagram of the first anti-Helmholtz coil in Embodiment 1 of the present invention;

[0039] Figure 6 It is a structural schematic diagram of a flat-top beam two-dimensional magneto-optical trap embodiment 2 of the present invention;

[0040] Figure 7 Schematic diagram of the structure of the first strip-shaped laser collimating beam expander in Example 2 of the present invention.

[0041] Figures 2 to 7 The following are the descriptions of the reference numerals:

[0042] 101-optical fiber; 100-laser collimator and beam expander; 200-first polarization beam splitter; 201-λ / 2 glass slide; 202-first free-form surface lens; 203-second free-form surface lens; 204-45 degree reflector; 205-third λ / 4 glass slide; 206-first 0 degree reflector; 300-second polarization beam splitter; 301-first λ / 4 glass slide; 302-third free-form surface lens; 303-fourth free-form surface lens; 304-fourth λ / 4 glass slide; 305-second 0 degree reflector; 400-ultra-high vacuum cavity; 401-first optical window; 402-second Optical window; 403-third optical window; 404-fourth optical window; 405-fifth optical window; 406-first anti-Helmholtz coil; 407-second anti-Helmholtz coil; 408-third anti-Helmholtz coil; 409-fourth anti-Helmholtz coil; 410-annular metal skeleton; 411-rectangular through groove; 501-first strip laser collimation expander; 502-second strip laser collimation expander; 503-metal shell; 504-third polarization splitter prism; 505-second λ / 4 glass slide; 506-fifth free-form surface lens; 507-sixth free-form surface lens. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings and exemplary embodiments.

[0044] Embodiment 1

[0045] Reference Figure 2 , Figure 3 A flat-top beam two-dimensional magneto-optical trap includes an ultra-high vacuum cavity 400, a cooling and trapping laser optical path system, a first group of anti-Helmholtz coil assemblies and a second group of anti-Helmholtz coil assemblies.

[0046] The ultra-high vacuum chamber 400 is a hollow rectangular parallelepiped made of non-magnetic metal, filled with atomic vapor, with a vacuum degree higher than 7×10 -5 Pa; the first optical window 401, the second optical window 402, the third optical window 403, the fourth optical window 404 and the fifth optical window 405 are respectively arranged on the five surfaces of the ultra-high vacuum cavity 400, the first optical window 401 is symmetrical with the second optical window 402, the third optical window 403 is symmetrical with the fourth optical window 404, and the first optical window 401, the second optical window 402, the third optical window 403 and the fourth optical window 404 are the same in size; the symmetric surface of the fifth optical window 405 is provided with a vacuum flange hole for connecting with other types of cold atom devices.

[0047] The first group of anti-Helmholtz coil components includes a first anti-Helmholtz coil 406 and a second anti-Helmholtz coil 407 respectively arranged on the outside of the first optical window 401 and the second optical window 402, and the second group of anti-Helmholtz coil components includes a third anti-Helmholtz coil 408 and a fourth anti-Helmholtz coil 409 respectively arranged on the outside of the third optical window 403 and the fourth optical window 404.

[0048] The cooling and trapping laser optical path system is used to generate a first uniform laser beam incident vertically from the first optical window 401, a second uniform laser beam incident vertically from the second optical window 402, a third uniform laser beam incident vertically from the third optical window 403, and a fourth uniform laser beam incident vertically from the fourth optical window 404. The beam cross-sections of the four uniform laser beams are rectangular, and the beam cross-sections are parallel beams with uniform light intensity distribution. The spot sizes and light intensities of the four uniform laser beams are equal; the optical axes of the first uniform laser beam and the second uniform laser beam coincide, and the optical axes of the third uniform laser beam and the fourth uniform laser beam coincide; the center lines of the optical axes of the first uniform laser beam and the third uniform laser beam intersect and are perpendicular. The first uniform laser beam, the second uniform laser beam, the third uniform laser beam, and the fourth uniform laser beam respectively trap atomic groups in four directions to form linear cold atomic beams, and the length of the cold atomic beam is equal to the length of the laser beam actually used to cool and trap atoms.

[0049] For the convenience of description, the long side direction of the beam cross section of the four uniform laser beams is defined as the Y axis, the short side direction is defined as the X axis, the Y axis is perpendicular to the X axis, and the Z axis is perpendicular to the plane where the Y axis and the X axis are located.

[0050] The cooling and trapping laser optical path system in this embodiment includes a light source, a laser collimating beam expander 100, a first polarizing beam splitter prism 200, a first optical path component, a second optical path component, a first reflector, and a second reflector.

[0051] Working material selection 87 Rb atoms, the wavelength of the light source is about 780.24nm, which is composed of the superposition of cooling light and re-pumping laser, and the frequency is relative to |5 2 S 1 / 2 , F=3>→|5 2 P 3 / 2 , F′=3>, the transition red detuning is 10~20MHz, and the total power is greater than 160mW. The frequency of the re-pump laser is |5 2 S 1 / 2 , F=1>→|5 2 P 3 / 2 , F′=2> transition resonance, the power is greater than 6mW.

[0052] The output end of the light source is connected to the input end of the laser collimator 100 through the optical fiber 101; the pump laser and the cooling light are coupled into the optical fiber 101 and then pass through the laser collimator 100 and the first polarization beam splitter prism 200 to be divided into two Gaussian laser beams with Gaussian cross-sectional light intensity distribution, and the polarization states of the two Gaussian laser beams are circular polarization or linear polarization.

[0053] A Gaussian laser beam forms a first uniform laser beam after passing through the first optical path component. The first uniform laser beam is vertically incident from the first optical window 401, and is reflected by the first reflector after being emitted from the second optical window 402 to form a second uniform laser beam. The second uniform laser beam is vertically incident from the second optical window 402; the first optical path component includes a λ / 2 glass slide 201, a first beam shaping lens group, and a 45-degree reflector 204 arranged in sequence along the propagation direction of the laser beam; the first beam shaping lens group includes a first free-form surface lens 202 and a second free-form surface lens 203 arranged in sequence along the propagation direction of the laser beam; the first reflector includes a third λ / 4 glass slide 205 and a first 0-degree reflector 206 arranged in sequence along the propagation direction of the first uniform laser beam.

[0054] Another Gaussian laser beam forms a third uniform laser beam after passing through the second optical path component. The third uniform laser beam is vertically incident from the third optical window 403, and is emitted from the fourth optical window 404 and reflected by the second reflector to form a fourth uniform laser beam. The fourth uniform laser beam is vertically incident from the fourth optical window 404; the second optical path component includes a second polarization beam splitter prism 300, a first λ / 4 glass plate 301, and a second beam shaping lens group arranged in sequence along the propagation direction of the laser beam; the second beam shaping lens group includes a third free-form surface lens 302 and a fourth free-form surface lens 303 arranged in sequence along the propagation direction of the laser beam; the second reflector includes a fourth λ / 4 glass plate 304 and a second 0-degree reflector 305 arranged in sequence along the propagation direction of the third uniform laser beam.

[0055] Figure 4 It is a uniform laser beam generated by the cooling trapped laser optical path system for cooling alkali metal atoms, and its beam cross section has a light intensity distribution along the Y-axis direction, L is the length of the cross section of the uniform laser beam along the Y-axis direction; when the device processing accuracy is high, the light intensity distribution of the uniform laser beam along the Y-axis direction is consistent with the solid line, and when the device processing accuracy is low, the light intensity distribution is consistent with the dotted line; the light intensity distribution of the uniform laser beam cross section along the X-axis direction is the same as the light intensity distribution along the Y-axis direction, so it will not be repeated.

[0056] The first beam shaping lens group and the second beam shaping lens group are used to shape a Gaussian laser beam with a Gaussian cross-sectional light intensity distribution into a uniform intensity laser beam with a uniform light intensity distribution on the beam cross section.

[0057] The λ / 2 glass slide 201 and the first λ / 4 glass slide 301 are both installed in a mounting base that can rotate around its geometric center to adjust the polarization of the laser beam; the λ / 2 glass slide 201 is adjusted so that the polarization state of the outgoing laser beam becomes left-handed circular polarization (σ-) / right-handed circular polarization (σ+), and the corresponding polarization states of the first uniform laser beam and the second uniform laser beam become right-handed circular polarization (σ+) / left-handed circular polarization (σ-); the first λ / 4 glass slide 301 is adjusted so that the polarization state of the outgoing laser beam becomes left-handed circular polarization (σ-) / right-handed circular polarization (σ+), and the corresponding polarization states of the third uniform laser beam and the fourth uniform laser beam become right-handed circular polarization (σ+) / left-handed circular polarization (σ-).

[0058] If the polarization states of the two Gaussian laser beams are linear polarization, the laser collimator and beam expander 100 only needs to be rotated around its own optical axis so that the transmitted light and reflected light powers of the two Gaussian laser beams are equal, thereby realizing the magneto-optical trap function.

[0059] The third λ / 4 glass slide 205 and the fourth λ / 4 glass slide 304 are both made of multiple square λ / 4 glass slides spliced ​​together, with a size of 70*25mm. When spliced ​​together, the fast axis and slow axis of the multiple square λ / 4 glass slides are installed in the same direction; the first 0-degree reflector 206 and the second 0-degree reflector 305 have a size of 70*25mm.

[0060] In the above optical elements, the light-transmitting surfaces of all transmitting optical elements are coated with anti-reflection films corresponding to the wavelength of the passing laser, and the reflective surfaces of all reflecting optical elements are coated with total reflection films with a reflectivity greater than 99.7% corresponding to the wavelength of the reflected laser.

[0061] Reference Figure 5 The first anti-Helmholtz coil 406, the second anti-Helmholtz coil 407, the third anti-Helmholtz coil 408 and the fourth anti-Helmholtz coil 409 have the same structure, and all include an annular metal skeleton 410; an annular groove is provided on the outer wall of the annular metal skeleton 410, and 250 turns of 1mm diameter copper enameled wire are wound in the annular groove; a rectangular through groove 411 is provided on the side wall of the annular metal skeleton 410 along the axial direction, and the rectangular through groove 411 is located on the symmetrical plane of the annular metal skeleton 410 along the axial direction, and a non-metallic non-conductive material with a matching shape, such as insulating bakelite, is provided in the rectangular through groove 411 to prevent the annular metal skeleton 410 from generating induced current when the coil is powered on and off.

[0062] The currents passing between the first anti-Helmholtz coil 406 and the second anti-Helmholtz coil 407, and between the third anti-Helmholtz coil 408 and the fourth anti-Helmholtz coil 409 are of the same magnitude and opposite direction, and are used to provide a magnetic field with a linear gradient for the flat-top beam two-dimensional magneto-optical trap and generate a magnetic field zero point at the symmetry center.

[0063] Example 2

[0064] Reference Figure 6 , Figure 7 In this embodiment, the configuration of the ultra-high vacuum chamber 400, the first group of anti-Helmholtz coil assemblies, and the second group of anti-Helmholtz coil assemblies are the same as those in Embodiment 1.

[0065] The cooling and trapping laser optical path system includes a light source, a first strip laser collimating beam expander 501 disposed on the first anti-Helmholtz coil 406 , a second strip laser collimating beam expander 502 disposed on the third anti-Helmholtz coil 408 , and a first reflector and a second reflector.

[0066] The arrangement of the light source is the same as that of Embodiment 1. The output end of the light source is connected to the input ends of the first strip-shaped laser collimating beam expander 501 and the second strip-shaped laser collimating beam expander 502 respectively through the optical fiber 101 .

[0067] After the pump laser and the cooling light are coupled into the optical fiber 101, they pass through the first strip laser collimation expander 501 to form a first uniform laser beam. The first uniform laser beam is vertically incident on the first optical window 401, and is emitted from the second optical window 402 and reflected by the first reflector to form a second uniform laser beam. The second uniform laser beam is vertically incident on the second optical window 402.

[0068] After the pump laser and the cooling light are coupled into the optical fiber 101, they pass through the second strip laser collimation expander 502 to form a second uniform laser beam. The second uniform laser beam is vertically incident on the third optical window 403, and is emitted from the fourth optical window 404 and reflected by the second reflector to form a fourth uniform laser beam. The fourth uniform laser beam is vertically incident on the fourth optical window 404.

[0069] The beam cross-section of the above four uniform laser beams is rectangular, and the beam cross-section is a parallel beam with uniform light intensity distribution. The spot size and light intensity of the four uniform laser beams are equal; the optical axis of the first uniform laser beam coincides with the optical axis of the second uniform laser beam, and the optical axis of the third uniform laser beam coincides with the optical axis of the fourth uniform laser beam; the center line of the optical axis of the first uniform laser beam and the center line of the optical axis of the third uniform laser beam intersect and are perpendicular. The first uniform laser beam, the second uniform laser beam, the third uniform laser beam, and the fourth uniform laser beam respectively trap atomic groups in four directions to form a linear cold atomic beam, and the length of the cold atomic beam is equal to the length of the laser beam actually used to cool and trap atoms.

[0070] For the convenience of description, the long side direction of the beam cross section of the four uniform laser beams is defined as the Y axis, the short side direction is defined as the X axis, the Y axis is perpendicular to the X axis, and the Z axis is perpendicular to the plane where the Y axis and the X axis are located.

[0071] The first uniform laser beam, the second uniform laser beam, the third uniform laser beam, and the fourth uniform laser beam have the same cross-sectional dimensions, and their lengths along the Y-axis direction are all 50 mm, and their lengths along the X-axis direction are all 18 mm.

[0072] The first strip-shaped laser collimation beam expander 501 and the second strip-shaped laser collimation beam expander 502 have the same structure and both include a metal shell 503. A third polarization beam splitter prism 504, a second λ / 4 glass plate 505, a fifth free-form surface lens 506, and a sixth free-form surface lens 507 are sequentially arranged in the metal shell 503 along the propagation direction of the outgoing light from the light source. The fifth free-form surface lens 506 and the sixth free-form surface lens 507 are used to shape a Gaussian laser beam with a Gaussian cross-sectional light intensity distribution into a uniform laser beam with a uniform light intensity distribution on the beam cross section.

[0073] Adjust the second λ / 4 glass plate 505 of the first strip laser collimation beam expander 501 so that the polarization state of its outgoing laser beam becomes left-handed circular polarization (σ-) / right-handed circular polarization (σ+), and the corresponding polarization states of the first uniform laser beam and the second uniform laser beam become right-handed circular polarization (σ+) / left-handed circular polarization (σ-); adjust the second λ / 4 glass plate 505 of the second strip laser collimation beam expander 502 so that the polarization state of its outgoing laser beam becomes right-handed circular polarization (σ+) / left-handed circular polarization (σ-), and the corresponding polarization states of the third uniform laser beam and the fourth uniform laser beam become left-handed circular polarization (σ-) / right-handed circular polarization (σ+).

[0074] The first reflector includes a third λ / 4 glass plate 205 and a first 0-degree reflector 206 sequentially arranged along the propagation direction of the first uniform laser beam; the second reflector includes a fourth λ / 4 glass plate 304 and a second 0-degree reflector 305 sequentially arranged along the propagation direction of the third uniform laser beam.

[0075] In the above optical elements, the light-transmitting surfaces of all transmitting optical elements are coated with anti-reflection films corresponding to the wavelength of the passing laser, and the reflective surfaces of all reflecting optical elements are coated with total reflection films with a reflectivity greater than 99.7% corresponding to the wavelength of the reflected laser.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. For ordinary professional and technical personnel in the field, the specific technical solutions recorded in the aforementioned embodiments can be modified, or some of the technical features therein can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions protected by the present invention.

Claims

1. A flat-top beam two-dimensional magneto-optical trap, comprising an ultra-high vacuum cavity (400), a cooling and trapping laser optical path system, a first set of anti-Helmholtz coil assemblies and a second set of anti-Helmholtz coil assemblies, characterized in that: The ultra-high vacuum cavity (400) is a hexahedral structure, and a first optical window (401), a second optical window (402), a third optical window (403), a fourth optical window (404) and a fifth optical window (405) are respectively arranged on its five surfaces, the first optical window (401) is symmetrical with the second optical window (402), the third optical window (403) is symmetrical with the fourth optical window (404), and the symmetric surface of the fifth optical window (405) is provided with a vacuum flange hole for connecting with other cold atom devices; The first group of anti-Helmholtz coil components comprises a first anti-Helmholtz coil (406) and a second anti-Helmholtz coil (407) respectively arranged outside the first optical window (401) and the second optical window (402); the second group of anti-Helmholtz coil components comprises a third anti-Helmholtz coil (408) and a fourth anti-Helmholtz coil (409) respectively arranged outside the third optical window (403) and the fourth optical window (404); The cooling trapped laser optical path system is used to generate a first uniform laser beam incident vertically from a first optical window (401), a second uniform laser beam incident vertically from a second optical window (402), a third uniform laser beam incident vertically from a third optical window (403), and a fourth uniform laser beam incident vertically from a fourth optical window (404), wherein the beam cross-sections of the four uniform laser beams are rectangular, and the beam cross-sections are parallel beams with uniform light intensity distribution, and the spot sizes and light intensities of the four uniform laser beams are equal; The optical axis of the first uniform laser beam and the optical axis of the second uniform laser beam coincide with each other, and the optical axis of the third uniform laser beam and the optical axis of the fourth uniform laser beam coincide with each other; the center line of the optical axis of the first uniform laser beam and the center line of the optical axis of the third uniform laser beam intersect and are perpendicular; The inner and outer surfaces of the window glass of the first optical window (401), the second optical window (402), the third optical window (403), and the fourth optical window (404) are coated with an anti-reflection film corresponding to the wavelength of the laser passing therethrough; The cooling trapped laser optical path system comprises a light source, a laser collimating beam expander (100), a first polarizing beam splitter prism (200), a first optical path component, a second optical path component, a first reflector and a second reflector; the output end of the light source is connected to the input end of the laser collimating beam expander (100) via an optical fiber (101); the output light of the light source passes through the laser collimating beam expander (100) and the first polarizing beam splitter prism (200) and is divided into two Gaussian laser beams; a Gaussian laser beam passes through the first optical path component to form a first uniform laser beam, and the first uniform laser beam passes through the first optical path component to form a first uniform laser beam. A light beam is vertically incident on the first optical window (401), and is emitted from the second optical window (402) and then reflected by the first reflector to form a second uniform laser beam, which is vertically incident on the second optical window (402); another Gaussian laser beam passes through the second optical path component to form a third uniform laser beam, which is vertically incident on the third optical window (403), and is emitted from the fourth optical window (404) and then reflected by the second reflector to form a fourth uniform laser beam, which is vertically incident on the fourth optical window (404); Alternatively, the cooling trapped laser optical path system comprises a light source, a first strip-shaped laser collimating beam expander (501) arranged on a first anti-Helmholtz coil (406), a second strip-shaped laser collimating beam expander (502) arranged on a third anti-Helmholtz coil (408), and a first reflector and a second reflector; the output end of the light source is respectively connected to the input ends of the first strip-shaped laser collimating beam expander (501) and the second strip-shaped laser collimating beam expander (502) through an optical fiber (101); the output light of the light source passes through the first strip-shaped laser collimating beam expander (501) to form a first uniform intensity laser The first uniform laser beam is vertically incident on the first optical window (401), and is emitted from the second optical window (402) and then reflected by the first reflector to form a second uniform laser beam, and the second uniform laser beam is vertically incident on the second optical window (402); the emitted light of the light source passes through the second strip-shaped laser collimating beam expander (502) to form a second uniform laser beam, and the second uniform laser beam is vertically incident on the third optical window (403), and is emitted from the fourth optical window (404) and then reflected by the second reflector to form a fourth uniform laser beam, and the fourth uniform laser beam is vertically incident on the fourth optical window (404).

2. A flat-top beam two-dimensional magneto-optical trap according to claim 1, characterized in that: The first optical path component comprises a λ / 2 glass plate (201), a first beam shaping lens group, and a 45-degree reflector (204) which are sequentially arranged along the propagation direction of the laser beam; and the second optical path component comprises a second polarization beam splitting prism (300), a first λ / 4 glass plate (301), and a second beam shaping lens group which are sequentially arranged along the propagation direction of the laser beam.

3. A flat-top beam two-dimensional magneto-optical trap according to claim 2, characterized in that: The first beam shaping lens group comprises a first free-form surface lens (202) and a second free-form surface lens (203) which are sequentially arranged along the propagation direction of the laser beam; and the second beam shaping lens group comprises a third free-form surface lens (302) and a fourth free-form surface lens (303) which are sequentially arranged along the propagation direction of the laser beam.

4. A flat-top beam two-dimensional magneto-optical trap according to claim 3, characterized in that: The λ / 2 glass slide (201) and the first λ / 4 glass slide (301) are both mounted in a mounting seat that can rotate around its geometric center.

5. The flat-top beam two-dimensional magneto-optical trap according to claim 1, characterized in that: The first strip-shaped laser collimating beam expander (501) and the second strip-shaped laser collimating beam expander (502) have the same structure and both comprise a metal shell (503), wherein a third polarization beam splitter prism (504), a second λ / 4 glass plate (505), a fifth free-form surface lens (506), and a sixth free-form surface lens (507) are sequentially arranged in the metal shell (503) along the propagation direction of the outgoing light of the light source.

6. A flat-top beam two-dimensional magneto-optical trap according to any one of claims 1 to 5, characterized in that: The first reflector comprises a third λ / 4 glass plate (205) and a first 0-degree reflector (206) which are sequentially arranged along the propagation direction of the first uniform laser beam; and the second reflector comprises a fourth λ / 4 glass plate (304) and a second 0-degree reflector (305) which are sequentially arranged along the propagation direction of the third uniform laser beam.

7. A flat-top beam two-dimensional magneto-optical trap according to claim 6, characterized in that: The first anti-Helmholtz coil (406), the second anti-Helmholtz coil (407), the third anti-Helmholtz coil (408) and the fourth anti-Helmholtz coil (409) have the same structure and all include an annular metal frame (410); an annular groove is provided on the outer wall of the annular metal frame (410), and a copper enameled wire is wound in the annular groove; a rectangular through groove (411) is provided on the side wall of the annular metal frame (410) along the axial direction, and the rectangular through groove (411) is located on the symmetrical plane of the annular metal frame (410) along the axial direction, and a non-metallic non-conductive material with a matching shape is provided in the rectangular through groove (411).

8. A flat-top beam two-dimensional magneto-optical trap according to claim 7, characterized in that: The third λ / 4 glass slide (205) and the fourth λ / 4 glass slide (304) are both formed by splicing a plurality of square λ / 4 glass slides, and when splicing, the fast axes and slow axes of the plurality of square λ / 4 glass slides are installed in the same direction.

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