Alkali metal Rydberg atom generation and detection device

Abstract

The invention discloses an alkali metal Rydberg atom generation and detection device which comprises a beam source cavity and an action cavity which are in butt joint through a vacuum flange. The beam source cavity comprises sputtering laser for preparing an alkali metal ultrasonic atom beam, an alkali metal solid target material, a high-pressure gas nozzle and a conical colander; the action cavity comprises exciting light, a repulsive electric field plate, a deceleration electric field plate, a grid mesh and a detector. Through holes are reserved between the repulsive electric field plate and the grid mesh so that atomic beams can pass through the through holes. According to the invention, cold alkali metal Rydberg atomic beams in concentrated distribution can be generated by combining ultrasonic atomic beams, laser sputtering and gradient electric field deceleration technologies, and intermittent detection is realized by applying pulse voltage, that is, detection is carried out only within the time range of ion collision with a detector. And the defects of overhigh alkali metal gas temperature caused by atomic furnace heating, noise influence caused by continuous pressurization detection and the like can be effectively overcome.

Description

Technical Field

[0001] The invention relates to the field of Rydberg atom dynamics in an external field, and in particular to an alkali metal Rydberg atom generation and detection device. Background Art

[0002] In the study of Rydberg atom dynamics in an external field, alkali metal Rydberg atoms are usually produced by heating an atomic furnace. The specific method is to heat the atomic furnace in a vacuum environment to sublimate the built-in solid alkali metal to produce hot atomic gas that diffuses to the entire vacuum cavity, and then excite it to the Rydberg state under laser pumping to form Rydberg atoms. The detection of Rydberg atoms generally uses a microchannel plate to collect the impact signal of the Rydberg atoms ionized by the electric field, which is the so-called flight mass spectrometry. However, this traditional method of producing and detecting alkali metal Rydberg atoms has the following disadvantages:

[0003] First, during the atomic generation process, the temperature of the heated alkali metal atomic gas is high and the atomic translational velocity is very large, which will greatly reduce the resolution of Rydberg atomic kinetic energy detection after ionization; second, during the atomic detection process, the continuous pressurization of the microchannel plate will record the messy background signal into the detection signal, which will seriously reduce the signal-to-noise ratio of the detection signal. Summary of the invention

[0004] In view of the shortcomings of the above-mentioned traditional alkali metal Rydberg atom generation and detection methods, the purpose of the present invention is to provide a device for generating and detecting alkali metal Rydberg atoms, which can generate a cold and concentrated alkali metal Rydberg atom beam by combining ultrasonic atomic beam, laser sputtering and gradient electric field deceleration technology, and realize intermittent detection by applying pulse voltage to the detector, that is, detection is only performed within the time range of the ion collision detector, which can effectively overcome the shortcomings of excessively high alkali metal gas temperature caused by atomic furnace heating and noise influence caused by continuous pressurized detection.

[0005] The present invention discloses an alkali metal Rydberg atom generation and detection device, the alkali metal Rydberg atom generation and detection device comprises a beam source cavity and an action cavity;

[0006] The beam source cavity is used to prepare an alkali metal ultrasonic atomic beam, and comprises a gas nozzle, a sputtering laser, an alkali metal solid target and a conical colander;

[0007] The gas nozzle extends into the cavity through the gas inlet rod, and is used to spray high-pressure carrier gas to generate an adiabatically expanded atomic gas mass; the alkali metal solid target is located at a position directly opposite to the atomic gas mass; the sputtering laser sputters the alkali metal solid target to generate gas-phase alkali metal atoms and diffuses into the atomic gas mass; the conical colander is fixed on the vacuum flange of the beam source cavity, and is located at a corresponding position where the alkali metal solid target generates gas-phase alkali metal atoms and diffuses into the atomic gas mass, and is used to pass through an ultrasonic atomic beam with a more concentrated velocity distribution at the center of the atomic gas mass;

[0008] The action chamber includes a Rydberg excitation region, a free flight region and a detector, and the Rydberg excitation region includes a repulsive electric field plate, an excitation light and a deceleration electric field plate;

[0009] The repulsive electric field plate is located on the side adjacent to the action cavity and the beam source cavity, and the repulsive electric field plate is connected to a positive voltage to blow away the alkali metal ions carried in the atomic beam; the excitation light is emitted into the action cavity through the optical window to excite the alkali metal atoms to the high Rydberg state, thereby preparing alkali metal Rydberg atoms; the deceleration electric field plate is a pair of parallel electrode plates, which are used to generate a horizontal gradient electric field to decelerate and cool the Rydberg atoms; the free flight zone includes two grounding grids; the detector includes at least two circular microchannel plates with high pressure, and the microchannel plates are installed on the vacuum flange of the action cavity away from the beam source cavity, and the external pressurizing equipment can apply high pressure through the electrodes to make the microchannel plates work normally.

[0010] Furthermore, the beam source chamber further comprises a rotary motor; the alkali metal solid target is mounted on the rotary motor to improve the stability of the sputtering signal, and the rotary motor is controlled by an external controller.

[0011] Furthermore, the beam source cavity further comprises a square metal box, the top of the square metal box, the incident direction of the sputtering laser and the side adjacent to the conical colander are all provided with openings, and the alkali metal solid target extends into the square metal box through the top opening;

[0012] The sputtering laser is injected into the interior of the square metal box through the opening, and generates gaseous metal atoms with the alkali metal solid target. The gaseous metal atoms are emitted through the opening on the side adjacent to the conical colander and diffuse into the atomic gas mass;

[0013] The square metal box is used to prevent the sputtering laser from reflecting and hitting the vacuum cavity to generate interference signals and to prevent the solid metal generated by sputtering from falling and adhering to the surface of the vacuum cavity.

[0014] Furthermore, the alkali metal Rydberg atom generation and detection device further includes a focusing lens;

[0015] The propagation direction of the sputtering laser is perpendicular to the direction of the atomic beam. After being focused by a focusing lens, the sputtering laser is transmitted through the optical window of the vacuum chamber into the chamber and hits the alkali metal solid target. Under the action of the laser, the solid alkali metal will quickly form a burn hole:

[0016]

[0017] Among them, ω0 is the beam waist radius, D is the hole size, E is the laser intensity, and E Th Threshold intensity.

[0018] Furthermore, the sputtering laser can change the light intensity and polarization state respectively by using a neutral density filter and a quarter wave plate, and the sputtering laser is circularly polarized to achieve uniformity in the diffusion direction of the sputtered atoms.

[0019] Furthermore, the deceleration electric field plate utilizes the large electric dipole moment of the Rydberg atoms to decelerate the Rydberg atoms through a horizontal gradient electric field. The force exerted on the atoms in the gradient electric field is:

[0020]

[0021] Among them, μ d is the electric dipole moment, which is proportional to the principal quantum number of the Rydberg state. is the electric field gradient.

[0022] Furthermore, the detector has three microchannel plates, each of which is pressed between stainless steel plates, screws are passed through the four corners of the stainless steel plates, the stainless steel plates are pressed and fixed on the screws with insulating materials such as polytetrafluoroethylene, and the screws are fixed on the vacuum flange;

[0023] The pressurizing device applies high voltage to the microchannel plate through electrodes. The high voltage application method of the microchannel plate adopts a combination of bias voltage and pulse voltage to ionize alkali metal Rydberg atoms and accelerate the ionized ions to reach the energy threshold of the microchannel plate response.

[0024] Furthermore, the excitation light is a pulsed laser with a frequency of 10 Hz and a pulse width of 10 ns.

[0025] Furthermore, the carrier gas is helium, and the vacuum in the vacuum chamber is maintained at 10 -6 Pa level.

[0026] Furthermore, the conical colander is made of stainless steel, and the diameter of the central circular hole is 30-100um. Different hole diameters can produce atomic beams with different divergence angles.

[0027] The beneficial effects achieved by the present invention are:

[0028] The present invention adds an alkali metal material laser sputtering device to the path of ultrasonic atomic beam generation, so that the gas-phase alkali metal atoms generated by laser sputtering are brought into the atomic beam, and after further excitation and gradient electric field deceleration, colder alkali metal Rydberg atoms can be prepared; on the other hand, the present invention applies a pulse voltage to make the detector work only within the time range of the measured particles reaching the detector, eliminating the accumulated background noise. Compared with the previous alkali metal Rydberg atom generation and detection methods, the present invention can greatly improve the Rydberg atom kinetic energy resolution and detection signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 An alkali metal Rydberg atom generation and detection device is provided in an embodiment of the present invention.

[0030] In the figure: 1-beam source chamber; 2-action chamber; 11-gas nozzle; 12-alkali metal solid target; 13-square metal box; 14-conical colander; 15-rotating motor; 16-sputtering laser; 17-focusing lens; 18-intake rod; 19-vacuum bellows; 20-displacement platform; 21-repulsive electric field plate; 22-excitation light; 23-deceleration electric field plate; 24-first grid; 25-second grid; 26-detector. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0032] like Figure 1 As shown, this embodiment provides an alkali metal Rydberg atom generation and detection device, including a beam source chamber 1 and an action chamber 2.

[0033] The beam source chamber 1 includes a gas nozzle 11, a sputtering light 16, an alkali metal solid target 12, a square metal box 13, a rotary motor 15 and a conical colander 14. The gas nozzle 11 extends to the inside of the vacuum chamber through an air inlet rod 18. The air inlet rod 18 is made of stainless steel and has a diameter of 1 cm. The other side of the air inlet rod is fixed on a displacement platform 20. The displacement platform 20 is connected to the beam source chamber through a vacuum bellows 19. The connection method of the vacuum bellows 19 not only ensures the vacuum degree, but also realizes the position adjustment. Therefore, the up and down, front and back, left and right positions of the gas nozzle 11 can be freely adjusted through the displacement platform 20, and the maximum adjustment range is 5 cm. After the high-pressure carrier gas passes through the gas nozzle 11, an adiabatically expanded atomic gas mass is formed. During the expansion process, the atomic velocity distribution is more concentrated due to the collision between atoms, and the temperature displayed is also lower.

[0034] The alkali metal solid target 12 is a cylindrical solid material, located to the right of the gas nozzle 11 and directly behind the atomic beam, with a vertical distance of about 1 cm from the atomic beam. It is also fixed in the slot of the structural member, which is fixed to the vacuum flange through a connecting rod. The slot can rotate freely under the drive of the rotary motor 15. The rotary motor is controlled by a controller outside the beam source cavity, and the motor is interconnected with the controller through the vacuum electrode on the vacuum flange.

[0035] The sputtering laser 16 is generated by an external laser, and the laser is preferably a continuous laser to avoid additional timing control of the sputtering laser 16, thereby simplifying the experimental scheme. The propagation direction of the sputtering laser 16 is perpendicular to the direction of the atomic beam. After being focused by a focusing lens 17 (focal length 15 cm), the sputtering laser 16 is transmitted through the optical window of the vacuum cavity into the cavity and hits the alkali metal solid target 12. Under the action of the laser, the solid alkali metal will quickly form a burn hole, and the size of the burn hole is proportional to the laser intensity E, which is:

[0036]

[0037] Among them, ω0 is the beam waist radius, E Th Threshold intensity.

[0038] The hole formation process is accompanied by the sputtering of plasma. In order to prevent the solid metal produced by sputtering from contaminating the vacuum cavity, the present invention designs a square metal box 13 to prevent the solid metal produced by sputtering from falling and adhering to the surface of the vacuum cavity. A circular hole is opened on the top of the square metal box 13, and the solid target can be placed inside. A circular hole is opened on the front surface for injecting the sputtering laser 16. The square metal box can limit the solid metal produced by sputtering from falling on the one hand, and prevent the sputtering laser 16 from reflecting and hitting the vacuum cavity to generate interference signals on the other hand. The gaseous metal atoms produced by sputtering are emitted through the small holes in the front of the square metal box 13 and diffuse into the carrier gas atom gas group to fully mix and cool with the carrier gas. The number of atoms produced by sputtering can be controlled by adjusting the laser light intensity.

[0039] In this embodiment, the light intensity and polarization state of the sputtering laser 16 can be changed respectively by using a neutral density filter and a quarter wave plate. The polarization of the sputtering laser 16 is preferably set to circular polarization to achieve uniformity in the diffusion direction of the sputtered atoms.

[0040] The conical colander 14 is fixed on the vacuum flange connected to the action chamber 2, and is used to extract the atomic beam with a more concentrated velocity distribution at the center. The conical colander 14 is made of stainless steel, and the diameter of the central circular hole is 30-100um. Different small hole diameters can produce atomic beams with different divergence angles. In this embodiment, the circular hole diameter is selected to be 50um.

[0041] In this embodiment, helium gas with more stable chemical properties is preferably used as the carrier gas. The high ionization potential of helium gas ensures that it will not be affected by the sputtering laser 16 and the excitation light 22. The high-pressure carrier gas of helium (about three atmospheres) is sprayed into the vacuum chamber through the gas nozzle 11 to form an adiabatic expansion of the atomic gas group. The vacuum in the vacuum chamber is maintained at 10 -6 At the same time, under the irradiation of the sputtering laser 16, the continuously rotating alkali metal solid target 12 produces stable gas-phase alkali metal atoms and diffuses, and a part of the alkali metal atoms collide with the expanding helium gas mass. In the continuous collision process, the speed of the alkali metal atoms gradually becomes consistent with the helium gas mass, and finally forms a mixed gas mass of alkali metal atoms and helium. The conical colander 14 further extracts the gas mass to form a mixed atomic beam with a more concentrated velocity distribution. The velocity distribution and the number of atoms of the atomic beam can be optimized by adjusting the left and right positions of the gas collision nozzle.

[0042] The beam source chamber 1 and the action chamber 2 are connected through a vacuum flange, and a circular hole with a diameter of 1 cm is opened on the vacuum flange for passing the atomic beam. The atomic beam entering the action chamber first passes through the repulsive electric field plate 21, which is a rectangular structure made of copper, and a circular hole with a diameter of 2 mm is opened in the center for passing the atomic beam. The repulsive electric field plate 21 is welded with copper wire and connected to the electrode of the vacuum flange. The external device applies a positive voltage to the electric field plate through the vacuum electrode on the flange. The positive voltage can effectively blow away the alkali metal ions generated by laser sputtering mixed in the atomic beam, so as to achieve the purpose of purifying the alkali metal atomic sample.

[0043] The preparation of the Rydberg state of the alkali metal atom is achieved by single-photon excitation, and the excitation light 22 is a pulsed laser with a frequency of 10 Hz and a pulse width of 10 ns. Different laser wavelengths correspond to different Rydberg states, and the efficiency of Rydberg state excitation is closely related to the intensity of the excitation light 22. In this embodiment, neutral density filters of different specifications are added to the propagation path of the excitation light 22 to adjust the intensity of the excitation light 22, and the tuning of the laser wavelength is achieved by scanning the frequency doubling crystal. The output of the laser pulse is triggered by an external signal, and the external trigger signal is generated by a signal generator.

[0044] Generally, the temperature of the atomic beam in the propagation direction is higher than that in the vertical direction. To further reduce the temperature of the atomic beam, it is necessary to decelerate the propagation direction, i.e., the horizontal direction. The present invention utilizes the large electric dipole moment characteristics of the Rydberg atom and decelerates the Rydberg atom through a horizontal gradient electric field. The force exerted on the atom in the gradient electric field is:

[0045]

[0046] Among them, μ d is the electric dipole moment, which is proportional to the principal quantum number of the Rydberg state. The horizontal gradient electric field is generated by a pair of horizontally placed electric field plates consisting of a deceleration electric field plate 23, the plates are copper rectangular structures, and the gradient of the horizontal electric field can be adjusted by the spacing between the plates.

[0047] The free flight zone in the action chamber is composed of a first grid 24 and a second grid 25. The grid is a rectangular mesh structure woven from copper wires. The distance between the two grids is set to 15 cm. The grid is welded with copper wires and connected to the electrodes of the vacuum flange. The vacuum electrode is grounded to achieve the grounding of the grid. The grounding of the grid can produce a free flight zone without electric field distribution. The free flight zone is a necessary condition for detecting the kinetic energy of Rydberg atoms using time resolution. The setting of the grid not only ensures the effect of electric field shielding, but also achieves the maximum flow of Rydberg atom beams, especially when Rydberg atoms are deflected. On this basis, the shielding effect of the electric field can be further improved by adding a shielding tube. The thin copper shielding tube is wrapped around the entire free flight zone to more thoroughly shield the external electromagnetic field interference.

[0048] A circular microchannel plate detector 26 is arranged on the far right of the action chamber. The diameter of the microchannel plate is 80 mm. The number of microchannel plates is preferably three, which can achieve the optimal amplification of the collision signal. The normal working pressure difference of the microchannel plate is at least 2000 V. In this embodiment, the microchannel plate is pressed between stainless steel plates, screws are passed through the four corners of the stainless steel plates, and the stainless steel plates are pressed and fixed on the screws with insulating materials such as polytetrafluoroethylene. The screws are fixed in the screw holes of the rightmost vacuum flange. The electrodes of the microchannel are led out through the flange. The pressure device applies high pressure to the microchannel plate through the electrodes. The high pressure can ionize the alkali metal Rydberg atoms on the one hand, and accelerate the ionized ions to reach the energy threshold of the microchannel plate response on the other hand. In order to more clearly illustrate the detection method, this embodiment does not show the structural parts for fastening in the accompanying drawings.

[0049] like Figure 1 As shown, the present invention adopts a unique detection voltage application method, the voltage application method is set to a combination of bias high voltage and pulse voltage, the bias high voltage is provided by a DC high voltage power supply, the pulse voltage is provided by a pulse voltage source, and the start of the pulse voltage source is controlled by an external trigger signal. The bias high voltage is set below the normal working voltage value of the microchannel plate, and the microchannel plate can only respond to the collision signal of the ion for detection when the bias high voltage and the pulse voltage are applied at the same time.

[0050] In actual operation, the pulse voltage and the trigger signal of the excitation light 22 maintain the same frequency and are set with a certain delay. The delay of the two trigger signals can be set by a pulse delay generator, so that the detector can only start detection when the Rydberg atom flies to the microchannel plate. This not only avoids the use loss caused by continuous operation of the detector, but more importantly, reduces the accumulated background noise and improves the signal-to-noise ratio of the detection.

[0051] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many forms of specific changes without departing from the scope of protection of the invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. An alkali metal Rydberg atom generation and detection device, characterized in that: The alkali metal Rydberg atom generation and detection device comprises a beam source chamber (1) and an action chamber (2); The beam source chamber (1) is used to prepare an alkali metal ultrasonic atomic beam, and comprises a gas nozzle (11), a sputtering laser (16), an alkali metal solid target (12) and a conical colander (14); The gas nozzle (11) extends into the cavity through the gas inlet rod (18) and is used to spray high-pressure carrier gas to generate an adiabatically expanded atomic gas mass; the alkali metal solid target (12) is located at a position directly opposite to the atomic gas mass; the sputtering laser (16) sputters the alkali metal solid target (12) to generate gaseous alkali metal atoms and diffuse into the atomic gas mass; the conical colander is fixed on the vacuum flange of the beam source cavity (1), located at a corresponding position where the alkali metal solid target (12) generates gaseous alkali metal atoms and diffuses into the atomic gas mass, and is used to pass through an ultrasonic atomic beam with a more concentrated velocity distribution at the center of the atomic gas mass; The action chamber (2) comprises a Rydberg excitation region, a free flight region and a detector (26), wherein the Rydberg excitation region comprises a repulsive electric field plate (21), an excitation light (22) and a deceleration electric field plate (23); The repulsive electric field plate (21) is located on a side of the action chamber (2) adjacent to the beam source chamber (1), and the repulsive electric field plate (21) is connected to a positive voltage for blowing away alkali metal ions carried in the atomic beam; the excitation light (22) is emitted into the action chamber (2) through the optical window, and is used to excite the alkali metal atoms to a high Rydberg state, thereby preparing alkali metal Rydberg atoms; the deceleration electric field plate (23) is a pair of parallel electrode plates, and is used to generate a horizontal gradient electric field to decelerate and cool the Rydberg atoms; the free flight zone includes two grounding grids; the detector (26) includes at least two circular microchannel plates with high pressure, and the microchannel plates are installed on a vacuum flange on the action chamber (2) away from the beam source chamber (1), and an external pressurizing device can apply high pressure through the electrodes to enable the microchannel plates to work normally.

2. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The beam source chamber (1) further comprises a rotary motor (15); the alkali metal solid target (12) is mounted on the rotary motor (15) to improve the stability of the sputtering signal; the rotary motor (15) is controlled by an external controller.

3. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The beam source chamber (1) further comprises a square metal box (13), the top of the square metal box (13), the incident direction of the sputtering laser (16) and the side adjacent to the conical colander (14) are all provided with openings, and the alkali metal solid target (12) extends into the square metal box (13) through the top opening; The sputtering laser (16) is injected into the interior of the square metal box through the opening, and generates gaseous metal atoms with the alkali metal solid target (12). The gaseous metal atoms are emitted through the opening on one side adjacent to the conical colander (14) and diffuse into the atomic gas mass; The square metal box (13) is used to prevent the sputtering laser (16) from reflecting and hitting the vacuum cavity to generate interference signals, and to prevent the solid metal generated by sputtering from falling and adhering to the surface of the vacuum cavity.

4. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The alkali metal Rydberg atom generation and detection device further comprises a focusing lens (17); The propagation direction of the sputtering laser (16) is perpendicular to the direction of the atomic beam. After being focused by the focusing lens (17), the sputtering laser (16) is transmitted through the optical window of the vacuum chamber into the chamber and hits the alkali metal solid target (12). Under the action of the laser, the solid alkali metal will quickly form a burn hole: Among them, ω0 is the beam waist radius, D is the hole size, E is the laser intensity, and E Th Threshold intensity.

5. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The sputtering laser (16) can change the light intensity and polarization state respectively by using a neutral density filter and a quarter wave plate, and the sputtering laser (16) is circularly polarized to achieve uniformity in the diffusion direction of sputtered atoms.

6. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The deceleration electric field plate (23) utilizes the large electric dipole moment characteristic of the Rydberg atoms to decelerate the Rydberg atoms through a horizontal gradient electric field. The force exerted on the atoms in the gradient electric field is: Among them, μ d is the electric dipole moment, which is proportional to the principal quantum number of the Rydberg state. is the electric field gradient.

7. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The detector (26) has three microchannel plates, each of which is pressed between stainless steel plates, screws are passed through the four corners of the stainless steel plates, the stainless steel plates are pressed and fixed on the screws with insulating materials such as polytetrafluoroethylene, and the screws are fixed on the vacuum flange; The pressurizing device applies high voltage to the microchannel plate through electrodes. The high voltage application method of the microchannel plate adopts a combination of bias voltage and pulse voltage to ionize alkali metal Rydberg atoms and accelerate the ionized ions to reach the energy threshold of the microchannel plate response.

8. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The excitation light (22) is a pulsed laser with a frequency of 10 Hz and a pulse width of 10 ns.

9. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The carrier gas is helium, and the vacuum in the vacuum chamber is maintained at 10 -6 Pa level.

10. The alkali metal Rydberg atom generation and detection device according to claim 1, characterized in that: The conical colander (14) is made of stainless steel, and the diameter of the central circular hole is 30-100 μm. Different small hole diameters are used to generate atomic beams with different divergence angles.

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