A beam source system for generating low-temperature molecules

Abstract

The present invention discloses a beam source system for generating low-temperature molecules, comprising a vacuum system, a pulse tube refrigerator, a gas reaction chamber, a gas pipeline, a flowmeter, a sample rod, a motor transmission device, a vacuum stepper motor, a motor driver, and a YAG laser. The present invention enables the low-temperature motor to drive the experimental sample rod to rotate continuously and stably at ultra-low temperatures; the YAG laser uniformly ablates the side surface of the sample rod, and an inert pre-cooled carrier gas is used to achieve the continuous and stable generation of low-speed and low-temperature atomic or molecular beams. The specially designed low-temperature motor has freely adjustable speed and ensures that, while the beam source is stable, motor heating will not cause the beam source cavity temperature to exceed 5K. Since the position of the YAG ablation focus does not need to be changed, the aerodynamic properties within the beam source cavity can be kept stable. The present invention has the advantages of high stability and good beam quality, and has significant application prospects in the field of atomic and molecular physics.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic and molecular physics, and in particular to a beam source system for generating low-temperature molecules. Background Art

[0002] Atomic and molecular beam sources are widely used in cold atomic and molecular physics, serving as a crucial initial step in almost any atomic and molecular physics experiment. For example, in atomic physics, where atomic beams cannot be generated at room temperature, a high-temperature furnace beam source is typically used. This method heats a single element of metal to a very high temperature, and atoms are then ejected from the furnace to create a stable beam source. This method achieves high beam density and high speed. In molecular physics, however, some research targets are not naturally present in large quantities. Therefore, a high-power pulsed YAG laser is used to bombard the surface of a single element sample to generate a plasma. This plasma then reacts with a reactive gas within the vacuum beam source chamber via chemical reactions. Alternatively, a sample of the desired molecule can be prepared in advance and bombarded with YAG to break a bond in the sample to produce the target molecule. Furthermore, a low-temperature environment and a low-temperature buffer gas can be used to pre-cool the generated molecules within the chamber, thereby reducing the molecular beam's velocity. It is believed that the spatial location where the YAG laser focuses on the sample surface corresponds to the location where the sample is sputtered each time. Due to the complex gas dynamics within the chamber, different sputtering locations affect the velocity and density of the emitted molecular beam. However, if the sample and the YAG light path remain stationary in space during the process of YAG light bombarding the sample, the focal position will become deeper and deeper, and even small depressions will appear on the sample surface under the action of YAG bombardment, causing the YAG light focusing path to become longer, the focus on the sample to become larger, and the depth to become deeper, which actually affects the stability of the molecular beam.

[0003] Therefore, a motor-driven mechanical structure that can rotate stably and continuously at a constant speed within the cryogenic chamber is required to ensure uniformity on the sample surface each time the YAG bombards the sample. At the same time, such a design must overcome issues such as motor outgassing in the high vacuum system, the thermal load imposed by the motor on the cryogenic beam source chamber, and mechanical structure seizure at cryogenic temperatures.

[0004] High-vacuum cryogenic motors can operate in ultra-high vacuum and cryogenic conditions. However, the Joule heating of the motors creates a significant load on the cryogenic system. Therefore, the motor current must be kept as low as possible while ensuring sufficient torque to drive the transmission system at low currents. Because the chamber cannot leak, the entrance where the sample rod enters the gas reaction chamber must be sealed, so the transmission structure must be completely fixed to the entrance of the gas reaction chamber. To address the thermal load, the transmission structure is entirely constructed of low-thermal-conductivity polyimide. This material exhibits much less deformation at low temperatures than metal, effectively mitigating screw thread jamming caused by thermal expansion and contraction.

[0005] In response to the problem that existing beam source technology cannot achieve stable generation of low-temperature molecular beam sources, the present invention proposes a beam source system for generating low-temperature molecules, which can effectively improve the stability of the molecular beam source and can be applied to cold atomic beam sources and any other scenarios that require controlling the rotation of samples in a low-temperature environment. Summary of the Invention

[0006] The main purpose of the present invention is to provide a beam source system for generating low-temperature molecules, which can effectively solve the problems in the background technology.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A beam source system for generating low-temperature molecules includes a vacuum system, a pulse tube refrigerator, a gas reaction chamber, a gas pipeline, a flow meter, a sample rod, a motor transmission device, a vacuum stepping motor, a motor driver, and a YAG laser. The top of the gas reaction chamber is tightly fixed to the pulse tube refrigerator, the sample rod is fixed to the upper side of the motor transmission device via black glue, the motor transmission device is fixed to the bottom of the gas reaction chamber, and the motor transmission device is fixedly mounted to the rotating shaft of the vacuum stepping motor.

[0009] The pulse tube refrigerator has a primary cold head and a secondary cold head. The extreme low temperature of the primary cold head can reach 30K, and the secondary cold head can reach 4K.

[0010] The programming of the rotation control of the vacuum stepping motor is realized by the motor driver and the control box;

[0011] The YAG laser has a laser energy of 10-20 mJ.

[0012] Preferably, the gas reaction chamber is made of copper.

[0013] Preferably, the first-stage cold head of the pulse tube refrigerator is in thermal contact with the vacuum stepping motor, the second-stage cold head of the pulse tube refrigerator is in close contact with the gas reaction chamber, and the contact surface between the second-stage cold head and the gas reaction chamber is filled with vacuum thermal grease or indium sandwich sheet.

[0014] Preferably, an inert gas is selected as the buffer gas, and the gas pipelines of the reaction gas and the buffer gas are respectively thermally isolated and thermally contacted with the secondary cold head of the pulse tube refrigerator, and the reaction gas and the buffer gas are respectively introduced into the gas reaction chamber through their respective gas pipelines.

[0015] Preferably, the motor transmission device includes an I-shaped fixing part, an M10 internal threaded part, an M10 external threaded part, an M3 head screw and a motor shaft sleeve. The top surface of the I-shaped fixing part and the bottom surface of the gas reaction chamber are fixed with screws. The M10 internal threaded part is tightly fitted with the upper circular hole of the I-shaped fixing part. The M10 external threaded part is sleeved on the outside of the motor shaft sleeve and is slidingly connected to the motor shaft sleeve. The M10 external threaded part is inserted into the M10 internal threaded part and is threadedly connected to the M10 internal threaded part.

[0016] Preferably, the outer surface of the motor shaft sleeve is tapped with an M3 threaded hole, the motor shaft sleeve is inserted into the shaft of the vacuum stepping motor, and the M3 head screw is threaded into the M3 threaded hole to fix the motor shaft sleeve to the shaft of the vacuum stepping motor.

[0017] Preferably, the side surface of the M10 external threaded part is provided with an adapting groove for matching with the M3 top screw, and the front end surface of the M3 top screw is located in the groove of the M10 external threaded part.

[0018] Preferably, the sample rod is glued to the top of the M10 external screw thread part by black glue.

[0019] Preferably, the I-shaped fixing piece, the M10 internal thread piece, the M10 external thread piece and the motor shaft sleeve are all made of polyimide material.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention realizes stable and continuous uniform rotation driven by a motor at ultra-low temperature. The sample rod can be evenly bombarded by the YAG ablation light, thereby generating a stable beam source. At the same time, the mechanical structure will not get stuck at low temperatures, and the heat generated by the motor will not excessively affect the temperature of the beam source cavity.

[0022] 2. The rotation speed of the sample rod of the present invention can be controlled in real time outside the cavity, and the structure is compact. Due to the short rotating shaft, the mechanical vibration during the transmission process is small, and since it is installed in the cavity, there is no restriction on the size of the external cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a front view block diagram of the beam source cavity and its motor drive of the present invention;

[0024] Figure 2 A detailed diagram of the transmission device of the present invention;

[0025] Figure 3 A comparison diagram of the thermal load of the motor of the present invention;

[0026] Figure 4 This is the beam source signal diagram of the present invention;

[0027] Figure 5 is the free flight time of the beam source of the present invention.

[0028] In the figure: 1. Gas reaction chamber; 2. Motor transmission device; 3. Vacuum stepping motor; 21. I-shaped fixing piece; 22. M10 internal thread fitting; 23. M10 external thread fitting; 24. M3 head screw; 25. Motor shaft sleeve. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0030] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," "the other end," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "connected," etc., should be understood in a broad sense. For example, "connected" may refer to a fixed connection, a detachable connection, or an integral connection; it may refer to a mechanical connection or an electrical connection; it may refer to a direct connection or an indirect connection through an intermediate medium; it may refer to internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0032] Example

[0033] A beam source system for generating low-temperature molecules includes a vacuum system, a pulse tube refrigerator, a gas reaction chamber 1, a gas pipeline, a flow meter, a sample rod, a motor transmission device 2, a vacuum stepping motor 3, a motor driver, and a YAG laser. The top of the gas reaction chamber 1 is tightly fixed to the pulse tube refrigerator. The sample rod is fixed to the upper side of the motor transmission device 2 with black glue. The motor transmission device 2 is fixed to the bottom of the gas reaction chamber 1. The motor transmission device 2 is fixed to the rotating shaft of the vacuum stepping motor 3.

[0034] Among them, the pulse tube refrigerator has a first-stage cold head and a second-stage cold head. The extreme low temperature of the first-stage cold head can reach 30K, and the second-stage cold head can reach 4K.

[0035] The programming of the rotation control of the vacuum stepper motor 3 is realized by the motor driver and the control box. The motor driver uses the DM420 driver of Yuheng Technology, and the control box uses the CL-01A model of Haijie Jiachuang. The subdivision of the motor driver is set to 1600, and the control cycle is set on the control box, with a pulse every 5 seconds and a total step length of 11200.

[0036] The YAG laser has an energy of 10-20 mJ and is focused on the side surface of the sample through a lens system with a focal length of 1 mm.

[0037] The gas reaction chamber 1 is made of copper.

[0038] The first-stage cold head of the pulse tube refrigerator is in thermal contact with the vacuum stepping motor 3, and the second-stage cold head of the pulse tube refrigerator is in close contact with the gas reaction chamber 1. The contact surface between the second-stage cold head and the gas reaction chamber 1 is filled with vacuum thermal grease or indium sandwich sheet to increase the contact area.

[0039] An inert gas is selected as the buffer gas. The gas pipelines of the reaction gas and the buffer gas are thermally isolated and in thermal contact with the secondary cold head of the pulse tube refrigerator, respectively. The reaction gas and the buffer gas are respectively introduced into the gas reaction chamber 1 through their respective gas pipelines. If a MgF molecular beam source is prepared, the inert buffer gas is selected to be helium with a concentration of 99.999%, and the reaction gas is selected to be nitrogen trifluoride with a concentration of 99.999%. The gas pipes of helium and nitrogen trifluoride gases are both made of copper tubes with an inner diameter of 2 mm. The helium copper tube is in thermal contact with the secondary cold head of the refrigerator, and the temperature is reduced to 4K. The end of the nitrogen trifluoride copper tube and the gas reaction chamber 1 are insulated with polyimide parts. At the same time, a copper braided wire is used to contact the primary cold head, and the temperature is reduced to 100K. The helium flow rate is set at 1 SCCM, and the nitrogen trifluoride flow rate is set at 0.24 SCCM. The flow meter uses the Qixing Huachuang brand.

[0040] like Figure 1-2 As shown, the motor transmission device 2 includes an I-shaped fixing part 21, an M10 internal threaded part 22, an M10 external threaded part 23, an M3 head screw 24 and a motor shaft sleeve 25. The top surface of the I-shaped fixing part 21 and the bottom surface of the gas reaction chamber 1 are fixed with screws, and a 0.5mm polyimide sheet is sandwiched in the middle to further reduce heat conduction. The M10 internal threaded part 22 is tightly matched with the upper circular hole of the I-shaped fixing part 21. The M10 external threaded part 23 is sleeved on the outside of the motor shaft sleeve 25 and is slidably connected to the motor shaft sleeve 25. The M10 external threaded part 23 is inserted and connected to the M10 internal threaded part 22 and is threadedly connected to the M10 internal threaded part 22.

[0041] The outer surface of the motor shaft sleeve 25 is tapped with an M3 threaded hole, and the motor shaft sleeve 25 is inserted into the shaft of the vacuum stepping motor 3. The M3 head screw 24 is threaded into the M3 threaded hole to fix the motor shaft sleeve 25 to the shaft of the vacuum stepping motor 3.

[0042] The side of the M10 external threaded part 23 is provided with an adapting groove for matching the M3 top screw 24. The front end face of the M3 top screw 24 is located in the groove of the M10 external threaded part 23. The rotation of the vacuum stepping motor 3 drives the motor shaft sleeve 25 and the M3 top screw 24 to rotate. One side of the M3 top screw 24 pushes the groove edge of the M10 external threaded part 23 to rotate it. Since the M10 internal threaded part 22 is fixed, the M10 external threaded part 23 is screwed in, so that the sample rod can be inserted into the gas reaction chamber 1.

[0043] The sample rod is glued to the top of the M10 external thread part 23 by black glue.

[0044] The I-shaped fixing piece 21 , the M10 internal thread piece 22 , the M10 external thread piece 23 and the motor shaft sleeve 25 are all made of polyimide material.

[0045] The specific operating steps of a beam source system for generating low-temperature molecules in this embodiment are as follows:

[0046] A: Before vacuuming, install the motor drive device 2 and the vacuum stepper motor 3 in the same way as above. Figure 1-2 For assembly and fixation, the sample rod needs to be fixed to the top of the M10 external screw thread part 23 with black glue in advance, and left to solidify for 10 hours. Then, use the manual mode of the motor control box to confirm whether the motor transmission device 2 is working properly at room temperature. After confirmation, switch the control box to automatic mode and select the cycle program that needs to be compiled;

[0047] B: Use a dry pump and a molecular pump to evacuate the air. When the vacuum is better than 4.5K, run the refrigerator again. Wait for 3-4 hours until the refrigerator reaches the limit temperature of about 4.5K. Then start the beam source system and detect the air.

[0048] C: Turn on the flow meter and set the flow rates of helium and nitrogen trifluoride to 1.0 SCCM and 0.24 SCCM respectively. Wait for 5-10 minutes for the gas dynamics in the chamber to reach equilibrium. Observe whether the vacuum reading is stable.

[0049] D: Turn on the motor switch, run the motor driver and control box, run the previously compiled cycle program, the motor starts working, and the sample rod starts to rotate; Figure 3As shown in the figure, when there is no motor heat load, the average temperatures of the secondary cold head of the refrigerator and the gas reaction chamber 1 are 4.0K and 4.2K respectively. When there is a motor heat load, the average temperatures of the secondary cold head of the refrigerator and the gas reaction chamber 1 are 4.3K and 4.6K respectively. Although the motor load in the present invention will cause the temperature of the system to rise slightly, the temperature rise is between 0.3-0.4K, and the thermal insulation performance is excellent.

[0050] E. Turn on the YAG laser and focus the beam on the side surface of the rotating sample rod. The sputtered magnesium reacts with nitrogen trifluoride gas to form magnesium monofluoride molecules. Cooled by helium, they are emitted from the outlet of gas reaction chamber 1 to form a stable pulsed molecular beam. At this time, we can use laser-induced fluorescence in the back cavity to detect the time-of-flight signal of the molecular beam using a photomultiplier tube; Figure 5 As shown, the two time-of-flight signals represent the signals when the molecules fly to the two detectors. The distance between the two detectors is 25 cm. We take the horizontal coordinates of the peak values ​​of the two signals, which correspond to the time when the molecular beam with the central velocity passes through the two detectors, which are 1.91 ms and 3.24 ms respectively. The time difference is 1.33 ms. By dividing the time difference by 25 cm, we can get the central velocity of the molecular beam under this pulse as 187 m / s. For an atomic and molecular beam source, the speed is very slow. At the same time, we arbitrarily take Figure 5 A curve is drawn, and the maximum value of the curve under this pulse is recorded. This maximum value represents the number of molecular beams in a single pulse. We record this value under each pulse and draw a curve with the number of pulses as the horizontal axis and the maximum value as the vertical axis. Figure 4 As shown in the figure, the number of molecular beams varies with the number of pulses. It can be seen that after nearly 7200 pulses for one hour, the molecular beam signal has hardly decreased, and the stability is also very good. The signal is continuously maintained at 0.8±0.2V. Compared with the traditional method of adjusting the focus or manually rotating the sample, the beam source effect after the implementation of the present invention is greatly improved. Figure 4 After we tested the stability of the sample, the YAG ablation focus on the side surface of the sample rod was a very uniform thread line.

[0051] The present invention realizes stable, continuous and uniform rotation driven by a motor at ultra-low temperature. The sample rod can be evenly bombarded by YAG ablation light, thereby generating a stable beam source. At the same time, the mechanical structure will not get stuck at low temperatures, and the heat generated by the motor will not excessively affect the temperature of the beam source cavity. The rotation speed of the sample rod can be controlled in real time outside the cavity. The structure is compact. Due to the short rotating shaft, the mechanical jitter during the transmission process is small. Moreover, since it is installed inside the cavity, there is no constraint on the size of the external cavity.

[0052] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A beam source system for generating low-temperature molecules, characterized by: The invention comprises a vacuum system, a pulse tube refrigerator, a gas reaction chamber (1), a gas pipeline, a flow meter, a sample rod, a motor transmission device (2), a vacuum stepping motor (3), a motor driver and a YAG laser, wherein the top of the gas reaction chamber (1) and the pulse tube refrigerator are tightly fixed, the sample rod is fixed to the upper side of the motor transmission device (2) by black glue, the motor transmission device (2) is fixed to the bottom of the gas reaction chamber (1), and the motor transmission device (2) is fixedly installed to the rotating shaft of the vacuum stepping motor (3); The pulse tube refrigerator has a primary cold head and a secondary cold head. The extreme low temperature of the primary cold head can reach 30K, and the secondary cold head can reach 4K. The programming of the rotation control of the vacuum stepping motor (3) is realized by the motor driver and the control box; The YAG laser has a laser energy of 10-20 mJ; The first-stage cold head of the pulse tube refrigerator is in thermal contact with the vacuum stepping motor (3), the second-stage cold head of the pulse tube refrigerator is in close contact with the gas reaction chamber (1), and the contact surface between the second-stage cold head and the gas reaction chamber (1) is filled with vacuum thermal grease or indium sandwich sheet; An inert gas is selected as a buffer gas, and the gas pipelines of the reaction gas and the buffer gas are respectively thermally isolated and thermally contacted with the secondary cold head of the pulse tube refrigerator, and the reaction gas and the buffer gas are respectively introduced into the gas reaction chamber (1) through their respective gas pipelines; The motor transmission device (2) includes an I-shaped fixing member (21), an M10 internal threaded member (22), an M10 external threaded member (23), an M3 head screw (24) and a motor shaft sleeve (25), wherein the top surface of the I-shaped fixing member (21) and the bottom surface of the gas reaction chamber (1) are fixed by screws, the M10 internal threaded member (22) and the upper circular hole of the I-shaped fixing member (21) are tightly matched, the M10 external threaded member (23) is sleeved on the outside of the motor shaft sleeve (25) and is slidably connected to the motor shaft sleeve (25), and the M10 external threaded member (23) is inserted and connected in the M10 internal threaded member (22) and is threadedly connected to the M10 internal threaded member (22); The outer surface of the motor shaft sleeve (25) is tapped with an M3 threaded hole, the motor shaft sleeve (25) is inserted into the shaft of the vacuum stepping motor (3), and the M3 head screw (24) is threadedly connected in the M3 threaded hole to fix the motor shaft sleeve (25) to the shaft of the vacuum stepping motor (3); The side surface of the M10 external threaded member (23) is provided with an adaptor groove for matching the M3 head screw (24), and the front end surface of the M3 head screw (24) is located in the groove of the M10 external threaded member (23); The sample rod is glued to the top of the M10 external threaded part (23) by black glue.

2. The low-temperature molecular beam source system according to claim 1, characterized in that: The material of the gas reaction chamber (1) is copper.

3. The beam source system for generating low-temperature molecules according to claim 1, characterized in that: The I-shaped fixing piece (21), the M10 internal thread piece (22), the M10 external thread piece (23) and the motor shaft sleeve (25) are all made of polyimide material.

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