Electromagnetic field restraint system and restraint method of CO2 laser amplifier

Abstract

The invention provides an electromagnetic field constraint system and constraint method for a CO2 laser amplifier, and the system comprises a spiral electrode which is wound on a discharge tube of the CO2 laser amplifier, the spiral electrode comprises a first DC positive electrode, a radio frequency positive electrode, a second DC positive electrode and a ground electrode which are sequentially and adjacently arranged, and the current flows through the first DC positive electrode in the electric field direction from the first DC positive electrode to the ground electrode. The electric field direction of the current from the second direct current positive electrode to the ground electrode is partially perpendicular to the electric field direction of the current from the radio frequency positive electrode to the ground electrode; the CO2 laser amplifier discharge tube and the Helmholtz coil are coaxially arranged, and the magnetic field direction of the Helmholtz coil is perpendicular to the electric field direction from the radio frequency positive electrode to the ground electrode. In the discharge area of the CO2 laser amplifier, the strong electromagnetic field restraint system is adopted, the vertical alternating high-voltage electric field and the vertical alternating high-voltage magnetic field are used for restraining plasma movement, the electro-optical conversion efficiency can reach about 20%, the CO2 laser power can be effectively improved, and the arc discharge problem under the high radio frequency power injection condition is avoided.

Description

Technical Field

[0001] This application relates to the field of laser amplifiers, and more specifically, to an electromagnetic field confinement system and method for a CO2 laser amplifier. Background Technology

[0002] Radio frequency fast axial-flow CO2 lasers are highly efficient lasers, with a commercially viable conversion efficiency of up to 20%, making them widely used in laser cutting, welding, drilling, and surface treatment. They possess significant commercial value.

[0003] In the previous development of high-power CO2 laser amplifiers, the gain capability of high-power CO2 laser amplifiers was mainly improved by increasing the electrical power and raising the gas pressure inside the CO2 laser amplifier.

[0004] There are two main ways to improve the gain of a CO2 laser amplifier: increasing the discharge injection power and increasing the intracavity gas pressure. Increasing the injection power leads to excessively high temperatures in the discharge region, increasing electron energy within the plasma, raising the electron collision frequency, and easily disrupting the originally uniform and stable discharge. Existing technologies primarily reduce the discharge region temperature by increasing the wind speed and optimizing the intracavity flow field structure. However, current magnetic levitation fan technology has reached its limit, and the wind speed in the discharge region is already close to the speed of sound, making further increases impossible. Optimizing the intracavity flow field using mechanical structures has also essentially reached its upper limit. In CO2 laser amplifiers, increasing the intracavity gas pressure can increase the number of inverted ions during the discharge process, thereby improving the gain of the CO2 laser amplifier. However, increasing the intracavity gas pressure increases the electron collision frequency, and currently, the intracavity gas pressure is already close to its upper limit; further increases will result in filamentary discharge, affecting the electro-optical conversion efficiency.

[0005] Therefore, an electromagnetic field confinement system and method for CO2 laser amplifiers are proposed to solve one of the aforementioned technical problems. Summary of the Invention

[0006] The purpose of this application is to provide an electromagnetic field confinement system and method for a CO2 laser amplifier, which can solve at least one of the aforementioned technical problems. The specific solution is as follows:

[0007] According to a specific embodiment of this application, this application provides an electromagnetic field confinement system for a CO2 laser amplifier, comprising:

[0008] A spiral electrode is wound around the discharge tube of a CO2 laser amplifier. The spiral electrode includes a first DC positive electrode, a radio frequency positive electrode, a second DC positive electrode, and a ground electrode arranged sequentially and adjacently. The electric field direction of the current from the first DC positive electrode to the ground electrode and the electric field direction of the current from the second DC positive electrode to the ground electrode are respectively partially perpendicular to the electric field direction of the current from the radio frequency positive electrode to the ground electrode.

[0009] The Helmholtz coil is coaxially arranged with the CO2 laser amplifier discharge tube, and the magnetic field direction of the Helmholtz coil is perpendicular to the electric field direction from the radio frequency positive electrode to the ground electrode.

[0010] In some embodiments, the two DC positive, RF positive, and ground electrodes arranged opposite each other have the same width and the same gap.

[0011] In some embodiments, the radio frequency positive electrode and the ground electrode are arranged opposite to each other.

[0012] In some embodiments, the magnetic field direction of the Helmholtz coil is the axial direction of the CO2 laser amplifier discharge tube; the electric field direction from the radio frequency positive electrode to the ground electrode is the radial direction of the CO2 laser amplifier discharge tube.

[0013] In some embodiments, the two ends of the spiral electrode are respectively assembled by two insulating components.

[0014] In some embodiments, the Helmholtz coil is provided with a water-cooled radiator.

[0015] In some embodiments, the formula for calculating the magnetic field B at the center of the Helmholtz coil is:

[0016]

[0017] Where μ0 is the vacuum dielectric constant, N0 is the number of coil turns, I is the current, and R is the coil radius.

[0018] According to a specific embodiment of this application, this application also provides a CO2 laser amplifier, including: multiple sets of the CO2 laser discharge tubes, including the system described above.

[0019] According to a specific embodiment of this application, this application also provides an electromagnetic field confinement method for a CO2 laser amplifier, the method comprising the following steps:

[0020] By applying a high-repetition-rate pulse voltage to the first DC positive electrode and the second DC positive electrode, seed electrons are generated in the CO2 laser discharge tube. When the number of seed electrons reaches a set number, the application of the high-repetition-rate pulse voltage is stopped.

[0021] By applying a high DC voltage to the first and second DC positive terminals, a high-voltage electric field is formed inside the CO2 laser discharge tube; at the same time, the CO2 laser amplifier is placed inside the Helmholtz coil to form a strong magnetic field.

[0022] By applying a high-voltage radio frequency to the positive electrode, the plasma inside the CO2 laser amplifier is excited. The strong magnetic field and high-voltage electric field, which are perpendicular to the radio frequency electric field, limit the activity of the plasma inside the CO2 laser discharge tube, thereby confining the plasma.

[0023] In some embodiments, the Helmholtz coil is wound around the wall of the CO2 laser discharge tube.

[0024] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects:

[0025] In the discharge region of a CO2 laser amplifier, this application utilizes a vertically alternating high-voltage electric field and a vertically alternating strong magnetic field to confine plasma motion, thereby further increasing electrical power and boosting gas pressure. This enhances the gain capability of the CO2 laser amplifier, increases plasma uniformity, and further improves electrical power injection and boosts gas pressure. The electro-optical conversion efficiency can reach approximately 20%, effectively increasing CO2 laser power and avoiding arcing problems under high RF power injection conditions. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0027] Figure 1 This is a schematic diagram of the first structure of an electromagnetic field confinement system for a CO2 laser amplifier provided in an embodiment of the present invention;

[0028] Figure 2 A cross-sectional view of an electromagnetic field confinement system for a CO2 laser amplifier provided in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of a CO2 laser amplifier structure provided in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram illustrating the application of an electromagnetic field confinement system for a CO2 laser amplifier, provided in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the second structure of an electromagnetic field confinement system for a CO2 laser amplifier provided in an embodiment of the present invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] In the figure, 1 is the first DC positive terminal, 2 is the radio frequency positive terminal, 3 is the second DC positive terminal, 4 is the ground terminal, 5 is the insulating component, 6 is the Helmholtz coil, 7 is the CO2 laser amplifier discharge tube, 8 is the first window, 9 is the second window, and 10 is the dimming module. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the article or device that includes said element.

[0036] In the development of existing high-power CO2 laser amplifiers, the gain capability is mainly improved by increasing the electrical power and raising the internal gas pressure. Under current discharge system conditions, further increasing the power or gas pressure will induce filamentary discharge within the CO2 laser discharge tube, affecting the photoelectric conversion efficiency of the CO2 laser amplifier. To ensure uniform discharge under high power and high pressure conditions, the commonly used method is to provide higher wind speeds; however, the performance of magnetic levitation fans has reached its limit and cannot be further improved. Increasing the internal gas pressure can increase the number of inverted ions during the discharge process, thereby improving the gain capability of the CO2 laser amplifier. However, increasing the internal gas pressure will increase the electron collision frequency, and the current internal gas pressure is already close to its upper limit; further increases will lead to filamentary discharge, affecting the electro-optical conversion efficiency.

[0037] This application provides an electromagnetic field confinement system for a CO2 laser amplifier, comprising: a spiral electrode wound around a discharge tube of the CO2 laser amplifier, the spiral electrode comprising a first DC positive electrode, a radio frequency positive electrode, a second DC positive electrode, and a ground electrode arranged sequentially adjacent to each other, wherein the electric field direction of the current from the first DC positive electrode to the ground electrode and the electric field direction of the current from the second DC positive electrode to the ground electrode are respectively partially perpendicular to the electric field direction of the current from the radio frequency positive electrode to the ground electrode; and a Helmholtz coil, wherein the CO2 laser amplifier discharge tube is coaxially arranged with the Helmholtz coil, and the magnetic field direction of the Helmholtz coil is perpendicular to the electric field direction from the radio frequency positive electrode to the ground electrode.

[0038] This application utilizes a strong electromagnetic field to confine high-energy plasma, increasing the uniformity of the radio frequency discharge plasma and further enhancing electrical power injection and increasing gas pressure. A strong electromagnetic field confinement system is employed to constrain plasma motion. This design significantly improves radio frequency injection power and gas pressure, ensuring the uniformity and stability of the discharge region under high power and high voltage conditions, and enhancing the gain capability of high-power CO2 laser amplifiers.

[0039] The following is in conjunction with the appendix Figure 1-5 Detailed description of optional embodiments of the present invention.

[0040] According to a specific embodiment of the present invention, this application provides an electromagnetic field confinement system for a CO2 laser amplifier, wherein the system is applied to a CO2 laser amplifier, such as... Figure 1 As shown, it includes a spiral electrode wound around the CO2 laser amplifier discharge tube 7. The spiral electrode includes a first DC positive electrode 1, a radio frequency positive electrode 2, a second DC positive electrode 3, and a ground electrode 4 arranged sequentially adjacent to each other. The electric field direction of the current from the first DC positive electrode 1 to the ground electrode 4 and the electric field direction of the current from the second DC positive electrode 3 to the ground electrode 4 are respectively partially perpendicular to the electric field direction of the current from the radio frequency positive electrode 2 to the ground electrode 4. For example, the CO2 laser amplifier discharge tube 7 is a quartz glass tube.

[0041] The Helmholtz coil 6 is coaxially arranged with the CO2 laser amplifier discharge tube 7, and the magnetic field direction of the Helmholtz coil 6 is perpendicular to the electric field direction from the radio frequency positive electrode 2 to the ground electrode 4. A relatively wide uniform magnetic field can be generated near the axial center of the Helmholtz coil 6. The formula for calculating the magnetic field B at the center of the Helmholtz coil 6 is:

[0042]

[0043] Where μ0 is the vacuum permittivity, N0 is the number of turns in the coil, I is the current, and R is the coil radius. For example, when the pulse current is set to 5kA and the number of turns in the Helmholtz coil 6 is 15, a uniform magnetic field of approximately 2700 Gauss can be obtained at the center. Two Helmholtz coils 6 are used. The laser electro-optic conversion efficiency of this application can be increased to 20%. With increasing injection power, stronger electric and magnetic fields are required for confinement.

[0044] In some embodiments, the first DC positive electrode 1, the radio frequency positive electrode 2, the second DC positive electrode 3, and the ground electrode 4 have the same width and the same gap. The circumferential distribution of the electric field intensity is reduced, eliminating local excessive breakdown points, lowering the ignition voltage, improving discharge uniformity, and directly reducing laser beam wavefront distortion.

[0045] In some embodiments, the radio frequency positive electrode 2 and the ground electrode 4 are arranged opposite to each other to form a radial radio frequency electric field. All radio frequency electric field lines penetrate the discharge core region, improving coupling efficiency and increasing plasma density under the same radio frequency power.

[0046] In some embodiments, the magnetic field direction of the Helmholtz coil 6 is the axial direction of the CO2 laser amplifier discharge tube 7; the electric field direction from the radio frequency positive electrode 2 to the ground electrode 4 is the radial direction of the CO2 laser amplifier discharge tube 7. For example... Figure 2 As shown, this electromagnetic field confinement system superimposes three fields—a high-voltage DC electric field, a radio frequency electric field, and an axial strong magnetic field—on the same CO2 laser amplifier discharge tube 7. This causes the plasma to be simultaneously subjected to a radial high-voltage DC electric field, a radial radio frequency electric field, and an axial static magnetic field. The radial high-voltage DC electric field provides axial drift force, rapidly pulling electrons / ions towards the ground pole and suppressing lateral diffusion. The radial radio frequency electric field maintains a high repetition rate and high uniformity of volume discharge, reducing the ignition voltage. The Lorentz force in the axial static magnetic field pulls electrons into a helical orbit along the magnetic field lines, further suppressing radial diffusion. The three fields are 90° orthogonal to each other, forming a "magnetic-electric cross-confinement" configuration.

[0047] In some embodiments, the two ends of the spiral electrode are respectively assembled by two insulating components 5 to fix the creepage distance between the high voltage area and the ground potential area.

[0048] In some embodiments, the Helmholtz coil 6 is internally equipped with a water-cooled heat sink. The Helmholtz coil 6 is coaxially mounted with the CO2 laser amplifier discharge tube 7, and the coil integrates water cooling without increasing the additional radial dimension; when multiple tubes are connected in series, they can be directly connected end to end to realize a high-energy "folded" amplification chain. The system volume is reduced by more than 30% compared with the traditional transverse excitation structure, ensuring constant gain over a long period of time; at the same time, the external fan is eliminated, reducing system noise.

[0049] According to a specific embodiment of this application, this application further provides a CO2 laser amplifier, including: multiple sets of the aforementioned CO2 laser discharge tubes, and also including the system described above. Figure 3 As shown, it also includes window glass located at both ends of the CO2 laser amplifier discharge tube 7. After the incident laser enters through the first window glass 8, it gains gain in the discharge region and then exits through the second window glass 9, forming a sealed gain cavity. The perpendicularity of the two windows to the optical axis is ensured by a single machining operation, improving the stability of the output laser. According to the CO2 laser gain formula, G = exp(g0l), where G is the small-signal gain, g0 is the small-signal gain factor, and l is the gain length, it can be seen that the CO2 laser gain is related to the length of the CO2 laser amplifier discharge tube 7. Therefore, in the design, the CO2 laser needs to pass through multiple amplification regions, such as... Figure 4 As shown, the CO2 laser beam, after passing through multiple CO2 laser amplifiers equipped with electromagnetic field confinement systems, obtains a final high-power CO2 laser beam which enters the dimming module 10. The dimming module 10 is mainly used to adjust the spot diameter and beam quality of the CO2 laser. After exiting the dimming module, the CO2 laser beam docks with the molten tin target in the EUV vacuum cavity.

[0050] According to a specific embodiment of this application, this application also provides an electromagnetic field confinement method for a CO2 laser amplifier, the method comprising the following steps:

[0051] By applying a high-repetition-rate pulse voltage to the first DC positive electrode 1 and the second DC positive electrode 3, the amplitude of the high-repetition-rate pulse voltage is greater than 20kV and the frequency reaches 10-1kHz, a large number of seed electrons are generated in the CO2 laser discharge tube 7, reducing the breakdown voltage. When the number of seed electrons reaches a set number, the application of the high-repetition-rate pulse voltage is stopped. The seed electron density is controllable and suitable for kHz high-repetition-rate amplification.

[0052] By applying a continuously operating DC high voltage to the first DC positive electrode 1 and the second DC positive electrode 3, the amplitude of the DC high voltage is greater than or equal to 10kV, and the specific voltage can be determined according to the RF power injection; a high-voltage electric field is formed inside the CO2 laser discharge tube 7; most of the electric field of the DC high voltage is perpendicular to the RF electric field, and a small part of the high-voltage electric field parallel to the RF electric field does not affect the normal operation of the entire system; at the same time, the CO2 laser amplifier is placed inside the Helmholtz coil 6 to form a strong magnetic field; a wide uniform magnetic field can be generated near the common axis center of the Helmholtz coil 6, which can ensure the magnetic field uniformity of the discharge plasma region;

[0053] By applying a high-voltage radio frequency (RF) of 13.56MHz and a power of ≥20kW to the RF positive electrode 2, the plasma inside the CO2 laser amplifier is excited. The strong magnetic field and high-voltage electric field perpendicular to the RF electric field limit the activity of the plasma inside the CO2 laser discharge tube, thereby confining the plasma and greatly improving the quantum efficiency.

[0054] By assembling the first window glass 8 and the second window glass 9, CO2 laser injection is performed on the CO2 laser amplifier, and the photoelectric conversion efficiency can reach about 20%, which effectively improves the CO2 laser power.

[0055] In some embodiments, such as Figure 5 As shown, the Helmholtz coil 6 can provide a strong magnetic field by winding it around the wall of the CO2 laser discharge tube 7. This method eliminates magnetic field gaps, achieves 100% magnetic field utilization, and ensures tight thermal contact between the winding and the wall of the CO2 laser discharge tube 7. The heat from the copper wire is dissipated through gas convection within the tube wall, further reducing the coil's water cooling flow requirement. This results in a more compact design and lower energy consumption.

[0056] This application offers more stable discharge, with RF-DC hybrid excitation lowering the breakdown threshold and magnetic field suppressing radial electron loss. This allows the discharge to be maintained stably under lower pressure and lower E / p conditions, eliminating arcing and filamentary discharge. The plasma density is significantly increased; electrons are confined within the tube by the magnetic field, resulting in a longer effective ionization path and a significantly higher electron density, achieving higher gain at the same pump power. The increased gain-length product allows for higher energy output from a single tube. Because radial diffusion is suppressed, the discharge region diameter d can be made smaller, while the effective gain length L remains constant, thus increasing the L / d ratio. This allows small-aperture tubes to achieve the gain of large-aperture conventional tubes, facilitating the creation of "slender" high-gain modules. Beam quality is improved; the radial dimension of the discharge region is "clamped" by the electric and magnetic fields, resulting in a clear plasma boundary and improved overlap between the gain region and the optical axis, leading to a smaller output laser spot diameter. Electro-optical efficiency is improved, with a 10%–20% reduction in ignition voltage and high electron utilization. At the same injection power, the laser output power is increased by 8%–15%, and the system's electro-optical conversion efficiency is significantly better than that of devices of the same size without magnetic field confinement. With a compact and modular structure, the Helmholtz coil and discharge tube are coaxially nested, and the coil is internally water-cooled without adding extra radial dimensions. When multiple tubes are connected in series, they can be directly connected end to end to realize a high-energy "folded" amplification chain. The system volume is reduced by more than 30% compared with the traditional transverse excitation structure.

[0057] In summary, this electromagnetic field confinement system, through "orthogonal electromagnetic field synergy," firmly confines the plasma near the optical axis, which not only improves gain and efficiency but also enhances beam quality and reliability. Thus, without increasing the volume, it achieves a triple leap in the performance of CO2 laser amplifiers: "high gain, high beam quality, and high repetition rate."

[0058] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to in the method section. This embodiment only describes an electromagnetic field structure designed using a Helmholtz coil and DC high voltage; other methods that utilize electromagnetic fields to confine plasma in a discharge region are within the scope of protection of this patent.

[0059] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An electromagnetic field confinement system for a CO2 laser amplifier, characterized in that, include: A spiral electrode is wound around the discharge tube of a CO2 laser amplifier. The spiral electrode includes a first DC positive electrode, a radio frequency positive electrode, a second DC positive electrode, and a ground electrode arranged sequentially and adjacently. The electric field direction of the current from the first DC positive electrode to the ground electrode and the electric field direction of the current from the second DC positive electrode to the ground electrode are respectively partially perpendicular to the electric field direction of the current from the radio frequency positive electrode to the ground electrode. The Helmholtz coil is coaxially arranged with the CO2 laser amplifier discharge tube, and the magnetic field direction of the Helmholtz coil is perpendicular to the electric field direction from the radio frequency positive electrode to the ground electrode.

2. The system according to claim 1, characterized in that, The two DC positive poles, radio frequency positive poles, and ground poles that are positioned opposite each other have the same width and the same gap.

3. The system according to claim 1, characterized in that, The radio frequency positive electrode and the ground electrode are arranged opposite each other.

4. The system according to claim 1, characterized in that, The magnetic field direction of the Helmholtz coil is the axial direction of the CO2 laser amplifier discharge tube; the electric field direction from the radio frequency positive electrode to the ground electrode is the radial direction of the CO2 laser amplifier discharge tube.

5. The system according to claim 1, characterized in that, The two ends of the spiral electrode are respectively assembled by two insulating components.

6. The system according to claim 1, characterized in that, The Helmholtz coil is equipped with a water-cooled radiator.

7. The system according to claim 1, characterized in that, The formula for calculating the magnetic field B at the center of the Helmholtz coil is: Where μ0 is the vacuum dielectric constant, N0 is the number of coil turns, I is the current, and R is the coil radius.

8. A CO2 laser amplifier, comprising: The plurality of CO2 laser discharge tubes are characterized in that they include the system described in any one of claims 1-7.

9. An electromagnetic field confinement method for a CO2 laser amplifier, implemented using the system described in any one of claims 1-8, characterized in that, The method includes the following steps: By applying a high-repetition-rate pulse voltage to the first DC positive electrode and the second DC positive electrode, seed electrons are generated in the CO2 laser discharge tube. When the number of seed electrons reaches a set number, the application of the high-repetition-rate pulse voltage is stopped. By applying a high DC voltage to the first DC positive terminal and the second DC positive terminal, a high-voltage electric field is formed inside the CO2 laser discharge tube; at the same time, the CO2 laser amplifier is placed inside the Helmholtz coil to form a strong magnetic field. By applying a high-voltage radio frequency to the positive electrode, the plasma inside the CO2 laser amplifier is excited. The strong magnetic field and high-voltage electric field, which are perpendicular to the radio frequency electric field, limit the activity of the plasma inside the CO2 laser discharge tube, thereby confining the plasma.

10. The method according to claim 9, characterized in that, The Helmholtz coil is wound around the wall of the CO2 laser discharge tube.

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