Small high-repetition pulsed photocathode electron gun

Abstract

This invention discloses a miniaturized high-repetition-rate pulsed photocathode electron gun, comprising a laser, a shaping optical path, and a photocathode electron gun arranged sequentially. The photocathode electron gun includes a front electrode and a quaternary electronic lens group. The laser serves as the light source for the shaping optical path, which precisely and stably transmits the laser beam to the photocathode surface. The cathode of the front electrode of the photocathode electron gun generates photoelectrons, and the front electrode controls the intensity of the emitted electron beam. The quaternary electronic lens group of the photocathode electron gun adjusts the uniformity of the emitted electron beam. This invention achieves high-quality electron beams while possessing advantages such as compact structure and miniaturization.

Description

Technical Field

[0001] This invention relates to the field of photocathode electron gun technology, and specifically to a small high-repetition-rate pulsed photocathode electron gun. Background Technology

[0002] A photocathode electron gun is an electron source generating device based on the photoelectric effect. It utilizes laser irradiation of a cathode material to excite electron emission, offering advantages such as low electron beam energy dispersion and high temporal resolution. It is widely used in electron collision experiments, ultrafast electron diffraction devices, and ultrafast electron microscopy. In electron scattering experiments, the energy dispersion of the electron beam itself introduces experimental errors, and the energy dispersion of the incident electron beam directly affects electron momentum resolution. Therefore, these research fields place high demands on the energy monochromaticity of the electron source. Traditional thermionic electron guns typically generate thermionic electrons by heating materials such as tungsten filaments, resulting in significant energy dispersion of the emitted electrons, which is insufficient for high-precision experiments. In contrast, the photocathode electron gun effectively reduces electron beam energy dispersion, significantly improving the accuracy and reliability of experimental data.

[0003] Currently, there are various photocathode electron gun structures. For example, patent application number 202510056026.6 discloses a 200 kV DC high-voltage photocathode electron gun; patent application number 202110027537.7 discloses a DC photocathode ultrafast electron gun with an immersion electrostatic lens.

[0004] The aforementioned technologies have improved the performance of electron guns to some extent, but they still have problems such as complex structure, limited control of electron beam energy dispersion, or insufficient system adaptability, making it difficult to achieve both structural miniaturization and high monochromatic electron beam output.

[0005] Therefore, it is necessary to provide a photocathode electron gun with a reasonable structure, small electron beam energy dispersion, and suitability for high-precision electron scattering experiments to overcome the shortcomings of the existing technology. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, the present invention provides a small high-repetition-rate pulsed photocathode electron gun, which can obtain a high-quality electron beam while having advantages such as compact structure.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A small high-repetition-rate pulsed photocathode electron gun includes, along the optical path direction, a laser, a shaping optical path and a photocathode electron gun arranged sequentially. The photocathode electron gun includes a front electrode and an electronic lens group. The front-end electrode includes a cathode, an extraction electrode, and an anode arranged in sequence. The laser source emitted by the laser is shaped by the shaping optical path and then transmitted to the cathode. The work function of the material used in the cathode is matched with the photon energy of the laser source. The electronic lens group includes multiple cylindrical electrodes arranged in sequence. The focusing effect of the electron beam output from the front-end electrode is adjusted by adjusting the voltage ratio of adjacent cylindrical electrodes.

[0008] The laser is used as a light source for the shaping optical path; The shaping optical path is used to precisely and stably transmit laser light to the photocathode surface; The cathode of the front electrode of the photocathode electron gun is used to generate photoelectrons, and the front electrode is used to control the intensity of the emitted electron beam. The quaternary electronic lens group of the photocathode electron gun is used to adjust the uniformity of the emitted electron beam.

[0009] The laser has a wavelength of 266 nm, the cathode is made of tantalum, the repetition frequency is 40 kHz, the pulse width is about 1 ns, and the single pulse energy is about 1 μJ.

[0010] The energy of the electrons emitted from the cathode is 0.55 eV.

[0011] The shaping optical path includes an attenuator, a high-reflection mirror one, a high-reflection mirror two, an optical lens one, an optical lens two, a focusing lens, and a quartz window; After the laser beam is emitted, it is attenuated by an attenuator. First, the optical path is collimated by high-reflection mirror one and high-reflection mirror two. Both high-reflection mirror one and high-reflection mirror two are placed at 45° to the optical path. The laser beam reflected by the high-reflection mirror is focused by a focusing lens and enters the 45° reflecting mirror on the photoelectron gun through a quartz window, irradiating the photocathode surface and exciting photoelectrons. Optical lenses 1 and 2 are set between the high-reflection mirror 1 and the high-reflection mirror 2. Optical lenses 1 and 2 are used for shaping to ensure uniform spatial distribution of the laser spot.

[0012] The focusing lens has two aperture stops, one on each side; aperture stop one is located between the focusing lens and the high-reflectivity mirror two, and aperture stop two is located between the focusing lens and the quartz window; the focal length of optical lens one is 100 mm, and the focal length of optical lens two is 200 mm; the focusing lens with a focal length of 350 mm is 350 mm away from the reflector on the photocathode electron gun.

[0013] The front-end electrode includes a cathode, an extraction electrode, and an anode; they are concentric, with the front-end located at the very front of the photoelectron gun and the extraction electrode located between the cathode and the anode.

[0014] The cathode is a 0.8 mm circular sheet made of tantalum. The work function of tantalum is 4.12 eV. The energy of the 266 nm photon matches the work function of the photocathode material. The energy dispersion of the electrons emitted from the tantalum cathode is about 0.55 eV, which gives the electron beam emitted from the photoelectron gun excellent monochromaticity.

[0015] The photocathode electron gun has a titanium shell with a work function of 4.9 eV, which reduces noise electrons generated by laser scattering within the electron gun. A negative voltage Uc is applied to the cathode filament, and a negative voltage U is applied to the extraction electrode. W U W A voltage less than Uc is generated to suppress electron emission, and the intensity of the emitted electron beam is controlled by adjusting the relationship between the extraction electrode voltage and the cathode voltage. A positive voltage U of 20V is applied to the anode. A The selected electron beam is then guided to the quaternary electronic lens group.

[0016] The electronic lens group is a quaternary electronic lens group, consisting of four cylindrical electrodes with a diameter of 7 mm and a length of 6 mm. The four cylindrical electrodes are U... L1 U L2 U L3 U L4 The potentials are unequal, and electric field lines with a lens-like curvature are generated between them. These lines act similarly to a lens, focusing or diverging the electron beam. By changing the voltage ratio between the different electrodes, U... L1 / U L2 =1 / 6, U L2 / U L3 =6, U L3 / U L4 =5, which generates a curved equipotential surface, subjecting electrons to an electric field force, thereby changing their trajectory and achieving the convergence or divergence of the electron beam.

[0017] The beneficial effects of this invention are: The electron beam monochromaticity of this invention is significantly improved. This invention uses a 266 nm ultraviolet laser to match the work function of the tantalum photocathode material, resulting in a narrower initial energy distribution of photoelectrons and an electron beam energy dispersion of approximately 0.55 eV, which is significantly lower than that of traditional thermionic electron guns, thereby improving the energy resolution and measurement accuracy of electron collision experiments.

[0018] This invention effectively suppresses stray electrons and improves the signal-to-noise ratio: by selecting titanium metal with high work function as the electron gun shell material, noise electrons caused by laser scattering are reduced, thereby improving the quality of the output electron beam and the experimental signal-to-noise ratio.

[0019] This invention has strong electron beam control capability and good adaptability: by setting the relationship between the extraction electrode voltage and the cathode voltage (U... W<Uc < 0), control the electron beam emission intensity.

[0020] The present invention has excellent focusing performance and flexible adjustment: a four - element electron lens group is adopted, and by changing the voltage ratio between different electrodes, the final beam bunching uniformity is good.

[0021] The photocathode electron gun of the present invention realizes miniaturization and has a compact structure. Brief Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the overall structure of a small high - repetition - rate pulsed photocathode electron gun of the present invention.

[0023] Figure 2 It is a schematic diagram of the structure of a front - end electrode and a four - element electron lens group of the present invention. Detailed Embodiment

[0024] The present invention will be further described in detail below with reference to the accompanying drawings.

[0025] A small high - repetition - rate pulsed photocathode electron gun in this embodiment includes a laser 1, a shaping optical path, a photocathode, a front - end electrode, and a four - element electron lens group.

[0026] In this embodiment, the wavelength of the laser 1 is 266 nm, the repetition frequency is 40 kHz, the pulse width is about 1 ns, and the single - pulse energy is about 1 μJ.

[0027] In this embodiment, the light source outlet of the laser 1 of the shaping optical path is at the same height as the shaping optical path. After the laser emits, it is attenuated by an attenuation sheet 2. First, the optical path is collimated by a high - reflection mirror 1 301 and a high - reflection mirror 2 302; both the high - reflection mirror 1 301 and the high - reflection mirror 2 302 are placed at 45° to the optical path.

[0028] During this period, the spatial distribution of the laser spot is ensured to be uniform through shaping by an optical lens 1 401 and an optical lens 2 402. The focal length of the optical lens 1 401 is 100 mm, the focal length of the optical lens 2 402 is 200 mm, and the distance between them is 300 mm. After being focused by a focusing lens 403 with a focal length of 350 mm, it passes through a quartz window 6 and enters the photocathode electron gun 7, irradiating the surface of the photocathode to generate photoelectrons by excitation.

[0029] In this embodiment, the photocathode is a 0.8 - mm - diameter circular thin sheet, the material is tantalum, the work function of tantalum is 4.12 eV, the photon energy of 266 nm matches the work function of the photocathode material, and the energy dispersion of the electrons emitted from the tantalum cathode is about 0.55 eV.

[0030] The outer shell of the photocathode electron gun 7 is made of titanium, with a work function of 4.9 eV, which reduces noise electrons generated by laser scattering within the electron gun. To determine the position of the cathode sheet from outside the vacuum chamber, a 1.2A current can be applied to both ends of the cathode for preheating. The orange light emitted by the cathode fluorescence radiation can be observed through the quartz window 5 from outside the chamber, thus determining the position of the cathode sheet. At this time, the heights of aperture 501 and aperture 502 are adjusted so that the orange light observed when passing through the smallest aperture of the aperture is the brightest. This allows the determination of a straight line pointing towards the cathode sheet, which is the optical path of the laser irradiating the photocathode.

[0031] In this embodiment, the 0.2 nA photocurrent generated by the photocathode is monitored by a picoammeter, and the optical path is finely adjusted to maximize the photocurrent.

[0032] like Figure 2 As shown, the cathode, extraction electrode, anode, and quaternary electronic lens are all mounted on the housing, ensuring they are concentric. The distance between the cathode and extraction electrode is 1 mm, the distance between the extraction electrode and anode is 1 mm, and the electronic lens U... L1 1mm distance from the anode, electronic lens U L1 With electronic lens U L2 1 mm spacing, electronic lens U L2 With electronic lens U L3 1 mm spacing, electronic lens U L3 With electronic lens U L4 Spacing 1 mm.

[0033] In this embodiment, the front-end electrode includes a cathode, an extraction electrode, and an anode. A negative voltage Uc is applied to the cathode filament, and a negative voltage U is applied to the extraction electrode. W U W A voltage less than Uc generates an electric field that suppresses electron emission, and the intensity of the emitted electron beam is controlled by adjusting the extraction electrode voltage. A positive voltage U is applied to the anode. A The selected electron beam is then guided to the quaternary electronic lens group.

[0034] In this embodiment, the quaternary electronic lens group consists of four cylindrical electrodes with a diameter of 7 mm and a length of 6 mm. L1 U L2 U L3 U L4 Unequal potentials create electric field lines between them, similar to the curvature of a lens. These lines act like a lens, focusing or diverging the electron beam. By changing the voltage ratio between the different electrodes, U... L1 / U L2 =1 / 6, U L2 / U L3 =6, U L3 / UL4 =5, which can adjust the focusing of the electron beam.

[0035] Working principle of the invention: This invention provides a small, high-repetition-rate pulsed photocathode electron gun, such as... Figure 1 The photoelectron gun 7 has a relatively compact structure and is miniaturized compared to existing electron guns; the electron gun in this application is much smaller. Its working principle is based on the photoelectric effect and electrostatic field control mechanism to achieve the generation and adjustment of a highly monochromatic electron beam: First, a 266 nm laser generates an ultraviolet pulse laser, which is processed by a shaping optical path to output a stable beam. The shaping optical path includes optical elements such as an attenuator 2, an aperture, a reflector, and a focusing lens, used to shape and collimate the laser beam, ensuring a uniform spatial distribution. The focused laser beam enters the vacuum chamber through a quartz window and is guided by an internal reflector to irradiate the photocathode surface. When the laser irradiates the photocathode made of tantalum material, the photon energy is higher than its work function, triggering the photoelectric effect to generate photoelectrons. The small energy dispersion improves the monochromaticity of the electron beam. Simultaneously, the electron gun shell is made of titanium metal with a high work function, which effectively suppresses stray electron emission caused by laser scattering and reduces background noise. Subsequently, the photoelectrons are extracted under the action of an electric field, with a negative voltage Uc applied to the cathode and a negative voltage U applied to the extraction electrode. W And satisfy U W When the voltage is less than Uc, a suppressive electric field is formed between the two, which modulates the electron emission intensity. The filtered electrons are then subjected to a positive anode voltage U. A Under the influence of the electron beam, the electrons are accelerated and guided into the quaternary electronic lens assembly; after entering the lens assembly, different potentials U are applied to the four electrodes respectively. L1 U L2 U L3 U L4 The electron beam moves in a non-uniform electrostatic field, which acts like an optical lens, converging or diverging the electron beam. By adjusting the voltage ratio between the electrodes, the trajectory and spot size of the electron beam can be controlled, thereby obtaining a high-quality electron beam output that meets experimental requirements.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A small, high-repetition-rate pulsed photocathode electron gun, characterized in that, Along the optical path, there are a laser (1), a shaping optical path and a photocathode electron gun (7) arranged in sequence. The photocathode electron gun (7) includes a front electrode and an electronic lens group. The front electrode includes a cathode, an extraction electrode and an anode arranged in sequence. The laser source emitted by the laser (1) is shaped by the shaping optical path and then transmitted to the cathode. The work function of the material used in the cathode is matched with the photon energy of the laser source. The electronic lens group includes a plurality of cylindrical electrodes arranged in sequence. The focusing effect of the electron beam output from the front electrode is adjusted by adjusting the voltage ratio of adjacent cylindrical electrodes.

2. The miniature high-repetition-rate pulsed photocathode electron gun according to claim 1, characterized in that, The laser (1) is a 266 nm laser, and the cathode is made of tantalum.

3. A small high-repetition-rate pulsed photocathode electron gun according to claim 2, characterized in that, The energy of the electrons emitted from the cathode is 0.55 eV.

4. A miniature high-repetition-rate pulsed photocathode electron gun according to claim 1, characterized in that, The shaping optical path includes an attenuator (2), a high-reflection mirror one (301), a high-reflection mirror two (302), a lens one (401), a lens two (402), a focusing lens (403), and a quartz window (6); After the laser emitted from the laser (1), it is attenuated by the attenuator (2), and the optical path is collimated by the high-reflection mirror one (301) and the high-reflection mirror two (302); both the high-reflection mirror one (301) and the high-reflection mirror two (302) are placed at 45° to the optical path; The laser reflected by the high-reflection mirror 2 (302) is focused by the focusing lens (403) and enters the 45° reflecting mirror (701) on the photoelectron gun through a quartz window (6), irradiating the photocathode surface to generate photoelectrons; optical lens 1 (401) and optical lens 2 (402) are arranged between the high-reflection mirror 1 (301) and the high-reflection mirror 2 (302), and lens 1 (401) and lens 2 (402) are used for shaping to ensure uniform spatial distribution of the laser spot.

5. A miniature high-repetition-rate pulsed photocathode electron gun according to claim 4, characterized in that, The focusing lens (403) has two aperture stops on either side, namely aperture stop one (501) and aperture stop two (502); aperture stop one (501) is located between the focusing lens (403) and the high-reflection mirror two (302), and aperture stop two (502) is located between the focusing lens (403) and the quartz window (6); The focal length of lens one (401) is 100 mm, and the focal length of lens two (402) is 200 mm; the focusing lens (403) with a focal length of 350 mm is 350 mm away from the reflector (701) on the photocathode electron gun.

6. A miniature high-repetition-rate pulsed photocathode electron gun according to claim 1, characterized in that, The front-end electrode includes a cathode, an extraction electrode, and an anode; they are concentric, with the front-end located at the very front of the photoelectron gun and the extraction electrode located between the cathode and the anode.

7. A miniature high-repetition-rate pulsed photocathode electron gun according to claim 6, characterized in that, The cathode is a circular thin sheet with a diameter of 0.8 mm.

8. A small high-repetition-rate pulsed photocathode electron gun according to claim 1, characterized in that, The outer shell material of the photocathode electron gun (7) is titanium metal; A negative voltage Uc is applied to the cathode filament, and a negative voltage U is applied to the extraction electrode. W U W The electric field is smaller than Uc, thus generating an electric field that suppresses electron emission and controls the intensity of the electron beam emission. The electron beam emission intensity is controlled by adjusting the relationship between the extraction electrode voltage and the cathode voltage. A positive voltage U of 20V is applied to the anode. A The selected electron beam is then guided to the quaternary electronic lens group.

9. A miniature high-repetition-rate pulsed photocathode electron gun according to claim 8, characterized in that, The electronic lens group is a quaternary electronic lens group, consisting of four cylindrical electrodes, wherein the four cylindrical electrodes are U L1 U L2 U L3 U L4 By changing the voltage ratio between different cylindrical electrodes, a curved equipotential surface is generated, which causes electrons to be subjected to force, thereby changing their trajectory and realizing the convergence or divergence of the electron beam. The voltage ratio between the cylindrical electrodes is set as follows: IN L1 / IN L2 =1 / 6,U L2 / IN L3 =6,U L3 / IN L4 =5.

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