A reflective beamsplitter and compact cold atom system apparatus

Abstract

The application discloses a reflection beam splitter and application thereof, and belongs to the field of cold atom sensing. The application integrates a fiber coupler, a beam collimation lens group, a half-wave plate assembly, a 1 / 4 wave plate assembly, an aperture assembly, an anti-Helmholtz coil, a micro vacuum chamber, a diffraction grating chip and a support device to form a small cold atom system device, so that the diffraction grating chip realizes the magnetic optical trap to capture a cold atom group and further quantum precision measurement. The application has the characteristics of single-beam input, chipping and miniaturization, and is movable. In combination with various light source modules and micro pumps, the application realizes the small and portable cold atom group binding function. In addition, the application realizes multiple diffraction beams through the diffraction grating chip from a single input beam, the two beams form a cooling optical trap, and the magnetic trap formed by the anti-Helmholtz coil is combined to realize a small magnetic optical trap. The application has the advantages of simple optical path alignment, small volume, easy integration and good robustness.

Description

Technical Field

[0001] The present invention relates to a small cold atom confinement device, and more particularly to a reflective beam splitter and a small cold atom system device including the reflective beam splitter, belonging to the field of cold atom sensing. Background Technology

[0002] Cold atom sensing systems utilize cold atoms, ultracold atoms, or even Bose-Einstein condensates (BECs) as sensing media. Through the interaction of light and magnetic fields with the cold atom medium, they achieve ultra-high precision and ultra-low drift quantum precision measurement platforms. Cold atom sensing systems involve complex devices such as high-power magneto-optical trap cooling systems, large vacuum chambers, and detection and timing control, resulting in large size, weight, and high power consumption, making them unsuitable for field applications. Therefore, reducing the size and weight of cold atom sensing systems, lowering their power consumption, and increasing the degrees of freedom of optical components to achieve miniaturized, portable, and mobile cold atom sensing systems is at the forefront of international research in this field. One of the key technologies of cold atom sensing systems is the magneto-optical trap. Traditional three-dimensional magneto-optical trap structures require six pairs of opposing laser beams and large Helmholtz coils. Their complex structure, high power consumption, high degrees of freedom, and difficulty in miniaturization severely limit the practical application of cold atom sensing systems.

[0003] To achieve miniaturization of cold atom systems, researchers have proposed diffraction grating chips for use in magneto-optical traps in recent years. Patent CN113960706A realizes a three-dimensional magneto-optical trap system with a planar grating and single-beam incident light, but lacks the adjustment of the incident beam mode and size. Patent CN114325930A realizes a laser multiplexing device for a triangularly arranged grating magneto-optical trap, but lacks the detection and adjustment of cold atoms. Patent CN114530270A realizes an independent integrated cold atom confinement device based on the magneto-optical trap principle, but does not reduce the number of laser beams.

[0004] This invention addresses key application problems in existing technologies by proposing a method and apparatus for beam adjustment in a miniature cold atom system reflective beam splitter. It achieves an adjustment scheme with single-beam input, adjustable incident beam, and adjustable beam overlap region. This scheme is combined with a miniature anti-Helmholtz magnetic coil and a miniature vacuum system to realize a miniature cold atom system for a diffraction grating. This invention can be applied to miniaturized, portable cold atom interferometers, gravimeters, gyroscopes, and other quantum precision measurement systems. Summary of the Invention

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] Firstly, a reflective beam splitter for use in a small cold atom device is provided, including an optical fiber coupler, a beam collimating lens assembly, and a half-wave plate assembly. 1 The / 4 glass slide assembly, aperture assembly, and diffraction grating chip are used in a small cold atom device. This allows the laser source to generate three positive first-order diffracted beams that intersect with the main beam at the beam intersection point, forming a four-beam balanced light field. The laser source sequentially passes through an fiber coupler, a beam collimating lens group, and a half-wave plate assembly. 1 / 4 Glass slide assembly, aperture assembly, and diffraction grating chip;

[0007] The beam collimating lens group (2) includes a collimating lens (211) and a beam expander (213) to achieve collimation and beam expansion of the light source laser;

[0008] The half-wave plate assembly includes a rotatable and adjustable half-wave plate, which converts the laser beam from the light source into linearly polarized light.

[0009] The 1 The / 4 slide assembly includes a rotatable and adjustable feature. 1 / 4 glass slides, enabling the conversion of linearly polarized beams into left- or right-hand circularly polarized light;

[0010] The aperture assembly includes an aperture to adjust the diameter of the beam spot; the main beam through the aperture assembly is incident perpendicularly on the diffraction grating chip, generating three positive first-order diffraction beams that intersect with the main beam at the beam intersection point, forming a four-beam balanced light field.

[0011] The optical axis of the half-wave plate and 1 / 4 glass slides have an optical axis difference of 45°;

[0012] The three positive first-order diffraction beams are positively distributed and form an angle of 55.3° with the direction of the vertical principal beam;

[0013] The grating period d of the diffraction grating chip is less than twice the incident laser wavelength λ.

[0014] The diffraction grating chip (9) has a grating period of d = 1.4 μm, and the light source laser is a cooling laser and a re-pump laser.

[0015] Preferably, the laser wavelength λ of the light source is 780nm.

[0016] A small cold atom device incorporating the aforementioned reflective beam splitter is further provided, comprising a laser light source, a coil assembly, and a vacuum assembly. The coil assembly includes a first anti-Helmholtz coil and a second anti-Helmholtz coil. The first anti-Helmholtz coil is located above the beam intersection point of the reflective beam splitter, and the second anti-Helmholtz coil is located below the beam intersection point of the reflective beam splitter, with the two coils symmetrically distributed vertically relative to the beam intersection point. The first and second anti-Helmholtz coils can form a quadrupole bound magnetic field. The center of the quadrupole bound magnetic field coincides with the beam intersection point of the reflective beam splitter. The vacuum assembly includes a vacuum chamber made of transparent material, which is disposed within the quadrupole bound magnetic field formed by the coil assembly and located between the first and second anti-Helmholtz coils. The vacuum assembly also includes a transition flange, an ion pump, and a thermal atom generator. The vacuum chamber is connected to the ion pump and the thermal atom generator via the transition flange.

[0017] The adapter flange connects the ion pump and the thermal atom generator via a four-way cavity; the four-way cavity also connects to a shut-off valve, which can shut off the channel between the vacuum chamber and the ion pump.

[0018] Both the first and second anti-Helmholtz coils are coaxial with the main beam. After being driven by the current source, the current in the first anti-Helmholtz coil is opposite to that in the second anti-Helmholtz coil, while the magnitude of the current remains the same.

[0019] Preferably, the vacuum chamber is made of quartz glass.

[0020] Preferably, the vacuum level of the vacuum chamber is 10. -7 Pa.

[0021] The positions of the first anti-Helmholtz coil (10) and the second anti-Helmholtz coil (13) can be adjusted up and down.

[0022] Optionally, the small cold atom device also includes a first observation camera (161), a second observation camera (162), and a third observation camera (163), which are respectively positioned to monitor the reflected light of the three positive first-order diffraction beams, in order to monitor the light intensity, polarization, and position of the three positive first-order diffraction beams. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the optical path of the beam adjustment device for the reflective beam splitter of the present invention;

[0024] Figure 2 This is a schematic diagram of the small cold atom system device of the present invention;

[0025] Figure 3 This is a schematic diagram of the observation and adjustment device of the small cold atom system device of the present invention;

[0026] Figure 4 It is the vacuum component;

[0027] Figure 5 It is the thermal atom generator

[0028] Figure 1 In the middle: 1-Fiber optic coupler, 2-Beam collimating lens group, 3-Half-wave plate assembly, 4-1 / 4-wave plate assembly, 5-Aperture assembly, 6-Main beam, 7-Beam intersection point, 8-Reflected diffraction beam set, 9-Diffraction grating chip, 10-First anti-Helmholtz coil, 11-Coil support, 12-Miniature vacuum chamber, 13-Second anti-Helmholtz coil, 14-Base, 15-System support column, 16-Observation camera, 17-Quadrupole confinement magnetic field, 18-Glass-metal adapter flange, 19-Ion pump, 20-Shut-off valve, 21-Four-way cavity, 22-Thermal atom generator Detailed Implementation

[0029] The invention is further defined below with reference to the accompanying drawings, but this should not be construed as limiting the scope of protection of the invention.

[0030] like Figures 1 to 4 As shown, this embodiment discloses a small cold atom system reflective beam splitter device. Figure 1 Reflective beam splitter, Figure 2 Small cold atom system device, Figure 3 The observation and adjustment device for a small cold atom system device, Figure 4 Vacuum components.

[0031] The reflective beam splitter, such as Figure 1 As shown, it includes an optical fiber coupler 1, a beam collimator 211, a beam expander 213, and a half-wave plate 311. 1 It consists of a glass slide 411, an aperture 511, and a diffraction grating chip 9.

[0032] The laser light source passes sequentially through fiber coupler 1, beam collimator 211, beam expander 213, and half-wave plate 311. 1 / 4 glass slide 411 and aperture 511 reach the diffraction grating chip 9.

[0033] The laser beam is incident on the beam collimator 211 via fiber coupler 1, forming a collimated beam with a diameter of 10 mm. The collimated beam is then incident on the beam expander 213, forming an expanded beam with a diameter of 15 mm. The expanded beam is then incident on the half-wave plate 311, forming a linearly polarized beam. The linearly polarized beam is then incident on... 1 / 4 glass plate 411, converting to left-handed (or right-handed) circularly polarized light (whereby ensuring that the optical axis of half-wave plate 311 is aligned with...) 1 / 4 The optical axes of the glass slide 411 differ by 45°. After the left-handed (or right-handed) circularly polarized light is incident on the aperture 511, the circularly polarized beam can be converted into a main beam 6 with a diameter of 20mm, depending on the size of the aperture of the aperture 511 (aperture value φ0~φ42mm).

[0034] The main beam 6 is incident on the diffraction grating chip 9 and is diffracted by the diffraction grating chip 9 to form a set of three reflected diffracted beams 8 at an angle of 55.3° to the vertical direction. These are the first reflected positive first-order diffracted beam 811, the second reflected positive first-order diffracted beam 812, and the third reflected positive first-order diffracted beam 813. The diameter of the main beam 6 is less than or equal to the diameter of the diffraction grating chip 9, which is 26 mm.

[0035] According to the Bragg equation for grating diffraction, dsinθ = mλ, where θ is the diffraction angle, d is the grating period, m is an integer, and λ is the incident light wavelength. For second-order and higher-order diffracted beams to be suppressed, |m| < 2, i.e., m = ±1. From the above equation, we can obtain d < 2λ (d = 1.4 μm, λ = 780 nm). That is, the grating period d is less than twice the incident light wavelength λ, ensuring that all higher-order diffracted beams except for the zeroth-order beam and the positive and negative first-order diffracted beams are suppressed after perpendicularly incident light passes through the grating diffractor.

[0036] Based on trigonometric relationships, the radius R of the diffraction grating is 13 mm, and the diffraction angle θ is 55.3°. Therefore, the highest point h of the beam intersection point 7 is h = R / tanθ = 9 mm.

[0037] The fiber coupler 1 couples the light source laser beam to the beam collimating lens group 2, wherein the light source laser includes a cooling laser and a repumping laser.

[0038] The small cold atom system device, such as Figure 2 As shown, it includes a laser light source, a reflective beam splitter, a coil assembly, and a vacuum assembly;

[0039] The reflective beam splitter includes an optical fiber coupler 1, a beam collimating lens group 2, and a half-wave plate assembly 3. 1 / 4 glass slide assembly 4, aperture assembly 5, and diffraction grating chip 9;

[0040] The coil assembly includes a first anti-Helmholtz coil 10, a coil support 11, a second anti-Helmholtz coil 13, a base 14, and a system support column 15;

[0041] The vacuum component, such as Figure 4 As shown, it includes a miniature vacuum chamber 12, a glass-metal transition flange 18, a 2L / s ion pump 19 with a CF16 connector, a shut-off valve 20, a four-way chamber 21, and a thermal atom generator 22.

[0042] The laser light source passes sequentially through fiber coupler 1, beam collimating lens group 2, and half-wave plate assembly 3. 1 / 4 glass slide assembly 4, aperture assembly 5, first anti-Helmholtz coil 10, miniature vacuum chamber 12, reaching diffraction grating chip 9;

[0043] The beam collimating lens group 2 consists of a collimating lens 211, a spacer 212, a beam expander 213, a spacer 214, and a collimating lens mount 215. Its main function is to achieve collimation and beam expansion of the laser source.

[0044] The half-wave plate assembly 3 comprises a half-wave plate 311, a half-wave plate mirror mount 312, a half-wave plate rotation adjustment knob 313, and a half-wave plate support 314, and its function is to convert the light beam into linearly polarized light.

[0045] The 1 / 4 glass slide assembly 4 includes 1 / 4 glass slide 411, 1 / 4 Slide mount 412, 1 / 4 Slide Rotation Adjustment Knob 413, 1 The glass slide support 414 is composed of a glass slide support, which functions to convert linearly polarized light beams into left-handed (or right-handed) circularly polarized light.

[0046] The aperture assembly 5 includes an aperture 511 and an aperture lens mount 512. The aperture 511 is mounted on the aperture lens mount 512 and its function is to adjust the diameter of the beam spot.

[0047] The second anti-Helmholtz coil 13 is disposed on the base 14;

[0048] The first anti-Helmholtz coil 10 is disposed between the aperture assembly 5 and the second anti-Helmholtz coil 13. The first terminal 101 of the first anti-Helmholtz coil is connected to the positive terminal of an external current source. The third terminal 131 of the second anti-Helmholtz coil is connected to the negative terminal of an external current source. The second terminal 102 of the first anti-Helmholtz coil is connected to the fourth terminal 132 of the second anti-Helmholtz coil, thereby forming a quadrupole bound magnetic field 17 (current set to 3 amperes).

[0049] The miniature vacuum chamber 12 of the vacuum assembly is made of quartz glass, with outer wall dimensions of 23 mm × 23 mm × 60 mm and a wall thickness of 1.5 mm. One side 12-1 of the chamber is bonded to the glass end face 18-1 of the glass-metal transition flange using epoxy resin vacuum adhesive, ensuring that the small hole in the center of the bottom surface is concentric with the glass end face 18-1 of the glass-metal transition flange. The CF16 flange of this vacuum chamber is then fixed to the left side of the four-way cavity 21 using M4 hexagonal screws.

[0050] The thermal atom generator 22, such as Figure 5For the thermal atom generator 22, two pins of the atom source 222 are fixed to the opposite two pins of the flange 223, which has four metal pins sealed, using vacuum terminals. Two pins of the vacuum getter 221 are fixed to the remaining two pins of the flange 223, ensuring that the four vacuum terminals do not touch each other. The continuity of the two pairs of pins is tested with a multimeter. Finally, the flange is fixed to the right side of the four-way cavity 21.

[0051] The 2L / s ion pump 19 with the CF16 interface, such as Figure 4 Ion pump 19, a 2L / s ion pump is fixed to the rear side of the four-way cavity 21 with an M4 hex screw.

[0052] The shut-off valve 20, such as Figure 4 Shut-off valve 20, fix the shut-off valve to the front side of the four-way cavity 21 with M4 hex socket screws.

[0053] The diffraction grating chip 9 is disposed on the base 14 and between the micro vacuum chamber 12 and the anti-Helmholtz coil 13, and is in close contact with the micro vacuum chamber 12.

[0054] The small cold atom system device of this design, based on the diameter R of the diffraction grating chip 9 (the diameter R of the diffraction grating chip in this experimental device is 10 mm), adjusts the diameter of the aperture 511 of the aperture assembly 5 to be smaller than the diameter 2R (15 mm) of the diffraction grating chip; slightly adjusts the position of the first anti-Helmholtz coil 10 up and down to ensure that the first anti-Helmholtz coil 10 and the second anti-Helmholtz coil 13 are symmetrical about the beam intersection point 7, so that the center of the quadrupole magnetic field generated by the first anti-Helmholtz coil 10 and the second anti-Helmholtz coil 13 coincides with the beam intersection point 7, thereby achieving the confinement and cooling of atoms.

[0055] The main optical path 6 is formed by the laser light source passing through the aforementioned beam collimating lens group 2 and half-wave plate assembly 3. 1 / 4 The beam formed after the glass slide assembly 4 and the aperture assembly 5 is matched with the size of the diffraction grating chip 9;

[0056] The beam intersection point 7 is the beam intersection point formed by the incident main beam 6 and the reflected diffraction beam set;

[0057] The reflected diffraction beam set 8 includes three or four reflected first-order diffraction beams, such as a first reflected positive first-order diffraction beam 811, a second reflected positive first-order diffraction beam 812, and a third reflected positive first-order diffraction beam 813, which function to form a balanced cross light field with the incident main light path 6; and a first reflected negative first-order diffraction beam 811-1, a second reflected negative first-order diffraction beam 812-2, and a third reflected negative first-order diffraction beam 813-3, which function to obtain a light intensity of 50mW for the positive first-order diffraction beam based on the symmetry of the positive and negative first-order diffraction.

[0058] The function of the diffraction grating chip 9 is to realize the formation of a balanced cross light field between the three reflected diffraction beam set 8 and the incident main beam 6;

[0059] The first anti-Helmholtz coil 10 and the second anti-Helmholtz coil 13 are respectively mounted on the coil support 11 and the base 14. The first terminal 101 of the first anti-Helmholtz coil is connected to the positive terminal of an external current source, the third terminal 131 of the second anti-Helmholtz coil is connected to the negative terminal of an external current source, and the second terminal 102 of the first anti-Helmholtz coil is connected to the fourth terminal 132 of the second anti-Helmholtz coil (the current in the first and second anti-Helmholtz coils is set to 3 amperes), thereby forming a quadrupole bound magnetic field 17.

[0060] The coil bracket 11 is used to fix the first anti-Helmholtz coil 10;

[0061] The base 14 is used to fix the system support column 15, the diffraction grating chip 9 and the second anti-Helmholtz coil 13.

[0062] The miniature vacuum assembly 12 is a quartz vacuum tube, which, together with the glass-metal transition flange 18, the CF16 connector 2L / s ion pump 19, the shut-off valve 20, the four-way cavity 21, and the thermal atom generator 22, provides a high vacuum environment (vacuum degree of 10). -7 Pa);

[0063] The system support column assembly 15 includes a first system support column 151, a second system support column 152, a third system support column 153, and a fourth system support column 154, and its function is to construct the support for the entire system device.

[0064] The observation device of the small cold atom system device is as follows Figure 3 As shown, it includes a first observation camera 161, a second observation camera 162, and a third observation camera 163;

[0065] Observation and adjustment procedures for a small cold atom system device:

[0066] 1. Set up the first observation camera 161, the second observation camera 162, and the third observation camera 163 respectively, with the first observation camera 161 aligned with the first negative first-order diffraction beam 811-1, the second observation camera 162 aligned with the second negative first-order diffraction beam 812-2, and the third observation camera 163 aligned with the third negative first-order diffraction beam 812-3. Based on the symmetry between the positive first-order diffraction beam and the negative first-order diffraction beam, measure the intensity, polarization, and position of the positive first-order diffraction beam (50mW, circularly polarized light, the intersection point 7 of the positive first-order diffraction beam is about 9mm away from the chip surface).

[0067] 2. Adjust the current magnitude of the first anti-Helmholtz coil 10 and the second anti-Helmholtz coil 13 respectively (current magnitude is 3A). Connect the first terminal 101 of the first anti-Helmholtz coil to the positive terminal of the external current source. Connect the third terminal 131 of the second anti-Helmholtz coil to the negative terminal of the external current source. Connect the second terminal 102 of the first anti-Helmholtz coil to the fourth terminal 132 of the second anti-Helmholtz coil (the current in the first and second anti-Helmholtz coils is set to 3 Amperes), thereby forming a quadrupole confinement magnetic field 17. Fine adjust the distance between the first anti-Helmholtz coil 10 and the second anti-Helmholtz coil 13 (0-15mm). The first anti-Helmholtz coil 10 and the second anti-Helmholtz coil 13 are symmetrical about the beam intersection point 7. The distance between the first anti-Helmholtz coil 10 and the beam intersection point 7 is 3mm, and the distance between the second anti-Helmholtz coil 13 and the beam intersection point 7 is 3mm.

Claims

1. A reflective beam splitter, comprising an optical fiber coupler (1), a beam collimating lens assembly (2), a half-wave plate assembly (3), a quarter-glass slide assembly (4), an aperture assembly (5), and a diffraction grating chip (9), for use in a small cold atom device, enabling a laser source to generate three positive first-order diffracted beams that intersect with the main beam at the beam intersection point, forming a four-beam balanced light field, characterized in that... The laser light source passes sequentially through the fiber coupler (1), the beam collimating lens group (2), the half-wave plate assembly (3), the quarter glass plate assembly (4), the aperture assembly (5), and finally reaches the diffraction grating chip (9); The beam collimating lens group (2) includes a collimating lens (211) and a beam expander (213) to achieve collimation and beam expansion of the light source laser; The half-wave plate assembly (3) includes a rotatable and adjustable half-wave plate (311) to convert the laser beam from the light source into linearly polarized light; The quarter-glass slide assembly (4) includes a rotatable and adjustable quarter-glass slide (411) that enables the conversion of linearly polarized beams into left-handed or right-handed circularly polarized beams. The aperture assembly (5) includes an aperture (511) to adjust the diameter of the beam spot; the main beam through the aperture assembly (5) is incident perpendicularly onto the diffraction grating chip (9) to generate three positive first-order diffraction beams that intersect with the main beam at the beam intersection point to form a four-beam balanced light field. The optical axis of the half-wave plate (311) differs from the optical axis of the quarter glass plate (411) by 45°; The three positive first-order diffraction beams are positively distributed and form an angle of 55.3° with the direction of the vertical principal beam; The diffraction grating chip (9) has a grating period d that is less than twice the incident laser wavelength λ.

2. A reflective beam splitter according to claim 1, characterized in that, The diffraction grating chip (9) has a grating period of d = 1.4 μm, and the light source laser is a cooling laser and a re-pump laser.

3. A reflective beam splitter according to claim 1, characterized in that, The laser wavelength λ of the light source is 780nm.

4. A miniature cold atom device comprising the reflective beam splitter according to any one of claims 1-3, characterized in that, It also includes the laser light source, coil components, and vacuum components; The coil assembly includes a first anti-Helmholtz coil (10) and a second anti-Helmholtz coil (13); the first anti-Helmholtz coil (10) is located above the beam intersection point of the reflector beam splitter; the second anti-Helmholtz coil (13) is located below the beam intersection point of the reflector beam splitter, and the two coils are symmetrically distributed vertically relative to the beam intersection point of the reflector beam splitter; the first anti-Helmholtz coil (10) and the second anti-Helmholtz coil (13) can form a quadrupole bound magnetic field; the center of the quadrupole bound magnetic field coincides with the beam intersection point of the reflector beam splitter. The vacuum assembly includes a vacuum chamber (12) made of transparent material, which is located within the quadruple confinement magnetic field formed by the coil assembly and between the first anti-Helmholtz coil and the second anti-Helmholtz coil. The vacuum assembly also includes a transition flange (18), an ion pump (19), and a thermal atom generator (22). The vacuum chamber (12) is connected to the ion pump (19) and the thermal atom generator (22) through the transition flange (18).

5. The miniature cold atom device according to claim 4, characterized in that, The adapter flange (18) connects the ion pump (19) and the thermal atom generator (22) through the four-way cavity (21); the four-way cavity (21) is also connected to the shut-off valve (20), which can realize the shut-off of the channel between the vacuum chamber (12) and the ion pump (19).

6. The miniature cold atom device according to claim 4, characterized in that, The first anti-Helmholtz coil (10) and the second anti-Helmholtz coil (13) are both coaxial with the main beam. After being driven by the current source, the current in the first anti-Helmholtz coil is opposite to the current in the second anti-Helmholtz coil, and the magnitude of the current remains the same.

7. The miniature cold atom device according to claim 4, characterized in that, The vacuum chamber (12) is made of quartz glass.

8. The miniature cold atom device according to claim 7, characterized in that, The vacuum level of the vacuum chamber is 10. - 7 Pa.

9. The miniature cold atom device according to claim 4, characterized in that, The positions of the first anti-Helmholtz coil (10) and the second anti-Helmholtz coil (13) can be adjusted up and down.

10. The miniature cold atom device according to claim 4, characterized in that, The small cold atom device also includes a first observation camera (161), a second observation camera (162), and a third observation camera (163), which are respectively positioned to reflect the light from the three positive first-order diffraction beams, in order to monitor the light intensity, polarization, and position of the three positive first-order diffraction beams.

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