Device for generating vortex electron beam based on magnetic immersion cathode

Abstract

The invention relates to the technical field of vortex electron beam preparation, and particularly discloses a device for generating a vortex electron beam based on a magnetic immersion cathode, which comprises an electrified solenoid, a laser output device, a photocathode device and an electromagnetic lens. The laser output device is used for outputting laser; the photocathode device is fixedly arranged in the electrified solenoid; the electromagnetic lens is fixedly arranged at the rear end of the electrified solenoid and is used for amplifying the section of the generated vortex beam; the photocathode device is of an annular photocathode structure or a low-temperature cooled photocathode structure; the device for generating the vortex electron beam based on the magnetic immersion cathode has the characteristics of simple structure, high generation efficiency and high flexibility, and is suitable for various equipment environments such as an electron accelerator and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of vortex electron beam preparation, and particularly relates to a device for generating a vortex electron beam based on a magnetic immersion cathode. Background Art

[0002] Vortex beams carrying orbital angular momentum have important applications in many fields such as optics, atomic and molecular physics, nuclear physics, materials science, biomedicine, chemistry, quantum information, and astrophysics. Vortex electrons are a new direction in the research of vortex beams in recent years. However, current experimental studies on vortex electron beams at home and abroad are still mainly based on electron microscopes, and the generated electron beam energy is about 300 keV. In addition, the main methods for generating vortex electrons include spiral phase plates, holographic gratings, and magnetic monopole methods. The flexibility and efficiency of these methods are relatively low, which limits the wide application of vortex electron beams. Therefore, new principles and methods for generating vortex electrons are an important part of the experimental research on vortex electrons. Based on Busch's theorem, electrons can generate Landau states in a magnetic field and be transmitted to regions outside the magnetic field to obtain a vortex electron beam with controllable angular momentum. The orbital angular momentum of the vortex electrons can be freely adjusted only by changing the magnetic field strength. Therefore, the magnetic immersion cathode is an efficient and flexible method for generating vortex electron beams. By using the magnetic immersion cathode method in an accelerator, high-energy vortex electron beams can be generated more effectively, providing a new way for studying the properties of high-energy vortex electrons and fields such as particle physics. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a device for generating a vortex electron beam based on a magnetic immersion cathode, which has the characteristics of simple structure, high generation efficiency, and strong flexibility, is applicable to various equipment environments such as electron accelerators, and can provide a new way for studying the properties of high-energy vortex electrons and fields such as particle physics.

[0004] To solve the above problems, the present invention adopts the following technical solutions:

[0005] A device for generating a vortex electron beam based on a magnetic immersion cathode includes an energized solenoid, a laser output device, a photocathode device, and an electromagnetic lens.

[0006] The laser output device is used to output laser.

[0007] The photocathode device is fixedly arranged inside the energized solenoid.

[0008] The electromagnetic lens is fixedly arranged at the rear end of the energized solenoid to magnify the cross-section of the generated vortex beam.

[0009] The photocathode device is a ring-shaped photocathode structure or a cryogenically cooled photocathode structure.

[0010] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, it further includes: a vacuum pipe, and the vacuum pipe has a vacuum window.

[0011] Wherein, the energized solenoid, the laser output device and the electromagnetic lens are all arranged inside the vacuum pipe.

[0012] The vacuum window is located at the front end of the energized solenoid, and the central axis of the vacuum window coincides with the central axis of the energized solenoid.

[0013] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, the photocathode device has a bracket.

[0014] The photocathode device is fixed inside the energized solenoid through the bracket, and the central axis of the photocathode device is collinear with the central axis of the energized solenoid.

[0015] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, the central axis of the electromagnetic lens is collinear with the central axis of the energized solenoid.

[0016] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, it further includes: a detector, a fluorescent screen and a CCD camera.

[0017] The detector, the fluorescent screen and the CCD camera are sequentially arranged behind the electromagnetic lens.

[0018] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, the detector is a microchannel plate detector.

[0019] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, the cryogenically cooled photocathode structure has a circulating cooling system.

[0020] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, it further includes: a collimating lens and a focusing lens.

[0021] The collimating lens, the focusing lens and the vacuum window are sequentially arranged along the optical path.

[0022] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, the photocathode device is a cryogenically cooled photocathode structure, and a spatial light modulator is further arranged between the focusing lens and the vacuum window.

[0023] The beneficial effects of the present invention are as follows: The method of the magnetic immersion cathode provided by the present invention can generate pure-mode vortex electrons, and has the characteristics of simple structure, high generation efficiency and strong flexibility, and is applicable to various equipment environments such as electron accelerators.

[0024] In the present invention, there are two schemes for the photocathode device that generates vortex electrons: The first scheme is that vortex light acts on a ring-shaped photocathode to ionize and generate vortex electrons; the second scheme is that a Gaussian laser irradiates a cryogenically cooled photocathode to generate vortex electrons. Both schemes of the method of the present invention follow Busch's theorem. For charged particles generated in a magnetic field, due to the conservation of their canonical orbital angular momentum, the particles still carry angular momentum when transmitted to a field-free region. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic principle diagram of a ring-shaped photocathode.

[0027] Figure 2 It is a schematic principle diagram of a cryogenically cooled photocathode.

[0028] Figure 3 It is a schematic structural diagram of the device for generating a vortex electron beam based on a magnetic immersion cathode in Embodiment 3.

[0029] Figure 4 It is a schematic structural diagram of the device for generating a vortex electron beam based on a magnetic immersion cathode in Embodiment 4.

[0030] In the figure:

[0031] 10. Energized solenoid;

[0032] 20. Photocathode device; 21. Bracket;

[0033] 30. Electromagnetic lens;

[0034] 40. Vacuum pipeline; 41. Vacuum window;

[0035] 50. Laser output device;

[0036] 60. Collimating lens;

[0037] 70. Focusing lens;

[0038] 80. Spatial light modulator;

[0039] 90. Microchannel plate detector;

[0040] 100. Fluorescent screen;

[0041] 110. CCD camera. Specific implementation manner

[0042] Next, the technical solutions in the embodiments will be clearly and completely described in conjunction with the accompanying drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments, rather than all the embodiments.

[0043] The device for generating a vortex electron beam based on a magnetic immersion cathode provided by at least one embodiment of the present disclosure includes an energized solenoid, a laser output device, a photocathode device, and an electromagnetic lens.

[0044] The laser output device is used to output laser. The photocathode device is fixedly arranged inside the energized solenoid. The electromagnetic lens is fixedly arranged at the rear end of the energized solenoid to magnify the cross-section of the generated vortex beam. The photocathode device is a ring-shaped photocathode structure or a cryogenically cooled photocathode structure.

[0045] In the device for generating a vortex electron beam based on a magnetic immersion cathode provided by at least one embodiment of the present disclosure, a vacuum pipeline is further included, and the vacuum pipeline has a vacuum window.

[0046] The energized solenoid, the laser output device, and the electromagnetic lens are all arranged inside the vacuum pipeline.

[0047] The vacuum window is located at the front end of the energized solenoid, and the central axis of the vacuum window coincides with the central axis of the energized solenoid.

[0048] In the device for generating a vortex electron beam based on a magnetic immersion cathode provided by at least one embodiment of the present disclosure, the photocathode device has a bracket.

[0049] The photocathode device is fixed inside the energized solenoid through the bracket, and the central axis of the photocathode device coincides with the central axis of the energized solenoid.

[0050] In the device for generating a vortex electron beam based on a magnetic immersion cathode provided by at least one embodiment of the present disclosure, the central axis of the electromagnetic lens coincides with the central axis of the energized solenoid.

[0051] In the device for generating a vortex electron beam based on a magnetic immersion cathode provided by at least one embodiment of the present disclosure, a detector, a fluorescent screen, and a CCD camera are further included.

[0052] The detector, the fluorescent screen, and the CCD camera are sequentially arranged behind the electromagnetic lens.

[0053] In the device for generating a vortex electron beam based on a magnetic immersion cathode provided by at least one embodiment of the present disclosure, the detector is a microchannel plate detector.

[0054] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, the cryogenically cooled photocathode structure has a circulating cooling system.

[0055] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, a collimating lens and a focusing lens are further included.

[0056] The collimating lens, the focusing lens, and the vacuum window are arranged in sequence along the optical path.

[0057] In the apparatus for generating a vortex electron beam based on a magnetically immersed cathode provided by at least one embodiment of the present disclosure, a spatial light modulator is further arranged between the focusing lens and the vacuum window.

[0058] According to Busch's theory, the initial mechanical orbital angular momentum of electrons generated in the central region of the solenoid is zero. Then the angular momentum of electrons when they are transmitted to the field-free space is or can be written as |l|≈1.5×10 -3 |Z|<ρ 2 >(nm 2 )H(T). Where e is the elementary charge, Z is the charge state of the ion, ρ is the width of the electron wave packet, and H is the magnetic field strength. That is, vortex electrons can be generated in the magnetic field, and the vortex electrons remain in the vortex state until they leave the solenoid.

[0059] The specific scheme for the annular photocathode to generate vortex electrons is as follows: The laser output by the laser output device is modulated in phase by the spatial light modulator after passing through the collimating lens and the focusing lens to generate vortex light, and then enters the vacuum pipeline from the observation window and acts on the annular photocathode to generate a pure-mode vortex electron beam. The transverse coherence of the electron beam is consistent with that of the vortex light and has a large transverse coherence length.

[0060] The specific scheme for the cryogenically cooled photocathode to generate vortex electrons is as follows: Cooling channels are processed inside the bracket, and the photocathode is kept at a low temperature through the circulating cooling system in the bracket, and the generated electrons have a low transverse momentum. The laser output by the laser output device passes through the collimating lens and the focusing lens and enters the vacuum pipeline from the observation window and acts on the cryogenic photocathode to generate vortex electrons.

[0061] To describe the present invention more specifically, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] Embodiment 1

[0063] As Figure 1 shown, the energized solenoid 10, the photocathode device 20, and the electromagnetic lens of the annular photocathode device for generating a vortex electron beam based on a magnetically immersed cathode are all installed in the vacuum pipeline 40.

[0064] After the energized solenoid 10 is energized, a uniform magnetic field is generated. The laser of the laser output device passes through the collimating lens and the focusing lens and then passes through the spatial light modulator. After the phase distribution of the laser is changed, vortex light is obtained. After the vortex light irradiates the left side of the annular photocathode device 20 in the energized solenoid 10, pure-mode vortex electrons are emitted outward on the right side of the photocathode device 20. In addition to the spatial distribution, the transverse momentum distribution of the electrons also needs to match the phase space of the Laguerre-Gaussian mode. According to Busch's theory, any charged particle generated in a magnetic field has conserved canonical orbital angular momentum, so the generated vortex electron beam still has orbital angular momentum after leaving the energized solenoid 10.

[0065] Example 2

[0066] As Figure 2 shown, the laser output by the laser output device passes through the vacuum window after collimation and focusing and acts on the cryogenic photocathode device 20 in the energized solenoid 10. The cryogenic photocathode device 20 is cooled by circulating liquid helium or liquid nitrogen in the bracket. The electrons emitted by the cryogenically cooled photocathode device 20 have very low transverse momentum, so a relatively large initial wave packet size can be obtained.

[0067] From the formula |l|≈1.5×10 -3 |Z|<ρ 2 (nm 2 )H(T), it can be obtained that the electrons generated in the magnetic field have a certain orbital angular momentum.

[0068] Example 3

[0069] As Figure 3 shown, the annular photocathode device for generating a vortex electron beam based on a magnetic immersion cathode includes an energized solenoid 10, a photocathode device 20, an electromagnetic lens 30, a vacuum pipe 40, a laser output device 50, a collimating lens 60, a focusing lens 70, a spatial light modulator 80, a microchannel plate detector 90, a fluorescent screen 100, and a CCD camera 110.

[0070] The photocathode device 20 is provided with a bracket 21, and a coolant circulation system (not shown) is provided inside the bracket 21.

[0071] The laser output device 50 outputs a laser. The output laser passes through the collimating lens 60 and the focusing lens 70 and then passes through the spatial light modulator 80 to generate vortex light. Subsequently, the vortex light enters the vacuum pipe 40 from the vacuum window 41. The energized solenoid 10 is installed in the vacuum pipe 40, and a uniform magnetic field is generated inside the energized solenoid 10 after energization.

[0072] The photocathode device 20 is fixed inside the energized solenoid 10 through the bracket 21. After its left side is irradiated by the focused laser, a pure-mode vortex electron beam is emitted from the right side. According to Busch's theory, the electrons optically excited in the magnetic field have quantum orbital angular momentum and remain in the vortex state when leaving the region of the energized solenoid 10.

[0073] The vortex electron beam obtained from the energized solenoid 10 is transmitted through the electromagnetic lens 30 installed downstream of the energized solenoid 10, and the transverse size of the beam current is enlarged. The "doughnut" pattern of the vortex electron beam is detected and observed using the microchannel plate detector 90, the fluorescent screen 100, and the CCD camera 110 at the rear end.

[0074] Embodiment 4

[0075] As Figure 4 shown, compared with Embodiment 3, no spatial light modulator is provided in this embodiment, and the shape of the photocathode device 20 is not annular. The photocathode device 20 is cooled by the coolant circulation system to keep the photocathode device 20 in a low-temperature state.

[0076] The laser output device 50 outputs laser light. The output laser light passes through the collimating lens 60 and the focusing lens 70 and then enters the vacuum pipe 40 from the vacuum window 41 to act on the cooled low-temperature photocathode device 20. After its left side is irradiated by the focused laser, a vortex electron beam is emitted from the right side. During the electron emission process, the circulating liquid helium or liquid nitrogen inside the bracket 21 of the photocathode device 20 cools the photocathode device 20. The generated vortex electron beam passes through the electromagnetic lens 30, and the transverse size of the beam current is enlarged and detected.

[0077] Although the embodiments of the present application have been shown and described above, the protection scope of the present invention is not limited thereto. Any change or replacement that can be thought of without creative work should be covered within the protection scope of the present invention; unless otherwise specified, any element, action, or instruction used in this article should not be construed as critical or essential.

Claims

1. A device for generating a vortex electron beam based on a magnetically immersed cathode, characterized in that: include: Energize the solenoid; A laser output device, used for outputting laser light; a photocathode device fixedly disposed in the energized solenoid; as well as An electromagnetic lens is fixedly arranged at the rear end of the energized solenoid and is used to amplify the cross section of the generated vortex beam; Wherein, the photocathode device is a ring-shaped photocathode structure or a low-temperature cooled photocathode structure.

2. The device for generating a vortex electron beam based on a magnetically immersed cathode according to claim 1, characterized in that: Also includes: A vacuum duct having a vacuum window; Wherein, the energized solenoid, the laser output device and the electromagnetic lens are all arranged in the vacuum pipe; The vacuum window is located at the front end of the energized solenoid, and the central axis of the vacuum window coincides with the central axis of the energized solenoid.

3. The device for generating a vortex electron beam based on a magnetically immersed cathode according to claim 1, characterized in that: The photocathode device has a bracket; The photocathode device is fixed in the energized solenoid through the bracket, and the central axis of the photocathode device is colinear with the central axis of the energized solenoid.

4. The device for generating a vortex electron beam based on a magnetically immersed cathode according to claim 1, characterized in that: The central axis of the electromagnetic lens is collinear with the central axis of the energized solenoid.

5. The device for generating a vortex electron beam based on a magnetically immersed cathode according to claim 1 or 2, characterized in that: Also includes: detector; Fluorescent screen; as well as CCD camera; Wherein, the detector, the fluorescent screen and the CCD camera are arranged in sequence behind the electromagnetic lens.

6. The device for generating vortex electron beam based on magnetically immersed cathode according to claim 5, characterized in that: The detector is a microchannel plate detector.

7. The device for generating vortex electron beam based on magnetically immersed cathode according to claim 1, characterized in that: The cryogenically cooled photocathode structure has a circulating cooling system.

8. The device for generating vortex electron beam based on magnetic immersion cathode according to claim 2, characterized in that: Also includes: Collimating lens; as well as Focusing lens; Wherein, the collimating lens, focusing lens and vacuum window are arranged in sequence along the optical path.

9. The device for generating vortex electron beam based on magnetically immersed cathode according to claim 8, characterized in that: The photocathode device is a low-temperature cooled photocathode structure, and a spatial light modulator is also arranged between the focusing lens and the vacuum window.

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