A method and device for preferentially selecting the lowest order waveguide mode by coating the electrode to control the electric field

Abstract

This invention relates to the field of waveguide gas laser technology, specifically to a method and device for preferentially controlling the electrode electric field to prioritize the lowest-order waveguide mode through coating, comprising the following steps: S1: determining the beam waist position of the laser resonator; S2: preparing an insulating coating on the surface of the waveguide laser electrode plate corresponding to the beam waist position; S3: performing a gradient transition edge treatment on the insulating coating; S4: constructing an impedance matching compensation network at the electrode feed end in the insulating coating region. This invention, by setting an insulating coating, achieves localized reduction of the electric field intensity in the beam waist region; simultaneously, by constructing an impedance matching compensation network, it accurately compensates for the capacitance effect introduced by the coating, and through dynamic monitoring and adjustment, ensures that the standing wave ratio and discharge voltage fluctuations are within a minimal range, guaranteeing effective coupling of RF power and uniform and stable discharge, thereby improving the overall efficiency and reliability of the device.

Description

Technical Field

[0001] This invention relates to the field of waveguide gas laser technology, specifically to a method and device for preferentially controlling the electrode electric field through coating to select the lowest order waveguide mode. Background Technology

[0002] In waveguide gas lasers, especially radio frequency excited CO2 lasers, the uniformity of discharge between electrodes and the electric field distribution directly determine the gain distribution, thus affecting the laser's mode characteristics. The presence of higher-order modes leads to an increase in beam divergence angle and a deterioration in the beam quality factor M², limiting the laser's application in precision machining, medical fields, and other areas. Traditional methods for suppressing higher-order modes include designing complex waveguide structures or using intracavity apertures, but these methods often increase losses, reduce efficiency, and offer limited improvement in beam quality.

[0003] Furthermore, under high-power operation, the electric field concentration effect at the electrode edges can easily induce gas breakdown, leading to unstable discharge and even device damage. Simultaneously, introducing insulating materials locally into the electrodes alters their impedance characteristics, affecting the effective coupling of RF power and causing discharge voltage fluctuations and efficiency degradation. Therefore, how to simply and effectively prioritize the excitation of the lowest-order waveguide mode while ensuring device operational stability is a pressing technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method and device for prioritizing the lowest-order waveguide mode by controlling the electrode electric field through coating, so as to solve the problem in the background art of how to simply and effectively prioritize the excitation of the lowest-order waveguide mode while ensuring the stability of device operation.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for controlling the electrode electric field through coating to preferentially select the lowest-order waveguide mode, comprising the following steps: S1: determining the beam waist position of the laser resonator; S2: preparing an insulating coating on the surface of the waveguide laser electrode plate corresponding to the beam waist position; S3: performing a gradient transition edge treatment on the insulating coating to avoid electric field concentration at the edge; S4: constructing an impedance matching compensation network at the electrode feed end in the insulating coating region to compensate for impedance changes; S5: utilizing the difference in conductivity between the insulating coating and the electrode substrate, locally weakening the electric field intensity in this region to form a free-space-like propagation region that preferentially selects the lowest-order waveguide mode.

[0006] Preferably, the coverage length of the insulating coating ranges from 0.3 to 0.8 times the Rayleigh length.

[0007] Preferably, the thickness of the insulating coating is 50-200μm, and the transmittance of its material at the laser working wavelength is ≥95%.

[0008] In a preferred embodiment of the present invention, the insulating coating is a multilayer composite structure, comprising:

[0009] Adhesive layer in contact with electrodes: 5-10μm thick, made of titanium or chromium, used to enhance adhesion;

[0010] A high-density ceramic layer covering the surface of the adhesive layer: with a thickness of 45-190μm, made of one or more of aluminum nitride, zirconium oxide or polyimide, with a dielectric strength ≥15kV / mm and a temperature resistance ≥300℃.

[0011] Preferably, the edge of the insulating coating has a transition zone with a gradually changing thickness, and the shape of the transition zone is a bevel or a rounded edge, with a width ≥ 2 mm.

[0012] As a preferred embodiment of the present invention, the impedance matching compensation network is composed of series-connected microstrip inductors, which are adjustable hollow inductors with an inductance of 10-15nH, used to compensate for the local capacitance effect introduced by the plating.

[0013] As a preferred embodiment of the present invention, the construction and adjustment of the impedance matching compensation network includes the following steps: 1. Measure the equivalent capacitance C of the insulating plating area. d Calculate the required inductance value;

[0014] 2. According to the formula L=1 / ((2πf)²C d Calculate the required inductance value L, where f is the RF excitation frequency (typically 40-100MHz).

[0015] 3. Adjust the microstrip inductance to the calculated value so that the overall standing wave ratio of the discharge region is ≤1.2;

[0016] 4. Install a voltage sampling probe in the insulating coating area to monitor the discharge voltage fluctuation ΔV in real time;

[0017] 5. When ΔV exceeds the 3% threshold, the adjustable capacitor / inductor of the matching network is driven by a stepper motor to adjust the impedance matching state and ensure that the discharge voltage fluctuation in the coating area is ≤3%.

[0018] The present invention also provides a device for implementing the above method, comprising:

[0019] A resonant cavity is a sealed cavity used to provide a space for photons to travel back and forth multiple times.

[0020] An electrode assembly is disposed inside the resonant cavity. The electrode assembly includes an upper electrode plate and a lower electrode plate, and a discharge region is formed between the upper electrode plate and the lower electrode plate. An insulating coating is disposed on the surface of the upper electrode plate and / or the lower electrode plate, and the disposed position corresponds to the beam waist region of the resonant cavity. The insulating coating is used to reduce the local electric field intensity of its covered area to suppress higher-order modes and preferentially output the lowest-order waveguide mode.

[0021] The front end group and the rear end group are respectively located at the front and rear ends of the resonant cavity to enable multiple reflections of photons along the axial direction within the cavity.

[0022] Preferably, both the upper electrode plate and the lower electrode plate have a copper tube with one end exposed inside; the front end assembly includes a front end cover, a semi-reflector, and an emission hole. The front end cover is fixed to the front end of the resonant cavity, and a semi-reflector is installed inside the resonant cavity at one end of the front end cover via a screw. An emission hole is formed on the surface of the front end cover; the rear end assembly includes a rear end cover and a total reflection mirror. The rear end cover is fixed to the rear end of the resonant cavity, and a total reflection mirror is installed inside the resonant cavity at one end of the rear end cover via a screw.

[0023] As a preferred embodiment of the present invention, the edge of the insulating coating is provided with a transition area, which is a bevel or a rounded edge with a width ≥ 2mm.

[0024] As a preferred embodiment of the present invention, the electrode input terminal corresponding to the insulating coating area is provided with an impedance matching compensation network to compensate for the impedance changes introduced by the coating.

[0025] The present invention also provides a waveguide gas laser comprising any of the devices described above, wherein the laser is a radio frequency excited CO2 laser.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. Prioritize output of the fundamental mode and significantly improve beam quality: By locally reducing the electric field intensity in the beam waist region through the insulating coating, a free space-like propagation region is artificially created in the center of the gain region, so that the fundamental mode (TEM00) can obtain better diffraction gain in this region, while higher-order modes are effectively suppressed due to their large spot size and high loss. Thus, without introducing an additional intracavity aperture, the fundamental mode is prioritized for output, significantly improving beam quality.

[0028] 2. Avoid electric field concentration and ensure discharge stability: By setting the edge of the insulating coating to a gradual transition structure and ensuring through simulation optimization that the electric field strength is below the breakdown threshold, the problem of electric field concentration and discharge breakdown caused by material abrupt changes is effectively avoided, ensuring the long-term stable operation of the device under high voltage.

[0029] 3. Compensating for impedance changes and improving power coupling efficiency: By constructing an impedance matching compensation network, the capacitance effect introduced by the coating is accurately compensated. Through dynamic monitoring and adjustment, the VSWR and discharge voltage fluctuations are kept within a very small range, ensuring effective coupling of RF power and uniform and stable discharge, thereby improving the overall efficiency and reliability of the device.

[0030] 4. Simple structure and easy to implement: This invention only requires adding a coating and matching network to the existing electrode structure, without changing the main structure of the laser. The process is simple, the cost is controllable, and it has good industrial applicability. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the external structure of the present invention;

[0032] Figure 2 This is a schematic diagram of the internal structure of the present invention;

[0033] Figure 3 This is a partially enlarged structural schematic diagram of the present invention;

[0034] Figure 4 This is a schematic diagram of the enlarged front-end assembly structure of the present invention;

[0035] Figure 5 This is a schematic diagram of the enlarged structure of the rear end assembly of the present invention;

[0036] Figure 6 This is a schematic diagram of the electrode assembly and impedance matching compensation network structure of the present invention;

[0037] In the diagram: 1. Resonant cavity; 2. Electrode group; 21. Upper electrode plate; 22. Lower electrode plate; 23. Discharge region; 24. Copper tube; 3. Front end group; 31. Front end cover; 32. Semi-reflector; 33. Emission hole; 4. Rear end group; 41. Rear end cover; 42. Total reflection mirror; 5. Insulating coating; 51. Transition region; 6. Impedance matching compensation network; 61. Microstrip inductor; 62. Voltage sampling probe. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] This invention provides a method for preferentially controlling the lowest-order waveguide mode by adjusting the electrode electric field through coating, such as... Figures 1 to 6As shown, the process includes the following steps: S1: Determine the beam waist position of the laser resonator; S2: Prepare an insulating coating 5 on the surface of the waveguide laser electrode plate corresponding to the beam waist position.

[0041] Among them, the coverage length of the insulating coating 5 ranges from 0.3 to 0.8 times the Rayleigh length, the thickness of the insulating coating 5 is 50-200μm, and its material has high transmittance at the laser working wavelength. S3: The insulating coating 5 is edged with a gradual transition to avoid the formation of electric field concentration at the edge, so that the local electric field strength is ≤2.4MV / m, and to avoid discharge breakdown.

[0042] The insulating coating 5 has a gradually changing thickness at its edge along its length to avoid electric field concentration. S4: An impedance matching compensation network is constructed at the electrode feed end of the insulating coating 5 to compensate for impedance changes, ensuring an overall standing wave ratio ≤1.2 and discharge voltage fluctuation ≤3%; S5: Utilizing the difference in conductivity between the insulating coating 5 and the electrode substrate, the electric field intensity in this region is locally reduced, forming a free-space-like propagation region that preferentially selects the lowest-order waveguide mode.

[0043] The present invention also provides a device for implementing the above method, comprising:

[0044] It includes a resonant cavity 1, an electrode group 2, a front end group 3, and a rear end group 4. The resonant cavity 1 provides a sealed cavity for the multiple round-trip propagation of photons, and can be filled with a laser working gas (such as a mixture of CO2, NO2, and He).

[0045] Furthermore, such as Figure 1 , Figure 2 and Figure 3 As shown, electrode group 2 is disposed inside resonant cavity 1. Electrode group 2 includes upper electrode plate 21 and lower electrode plate 22. A discharge region 23 is formed between upper electrode plate 21 and lower electrode plate 22. A copper tube 24 with one end exposed can be embedded inside upper electrode plate 21 and lower electrode plate 22 for passing cooling water to remove heat. An insulating plating layer 5 is disposed on the surface of upper electrode plate 21 and / or lower electrode plate 22, and the disposed position corresponds to the beam waist region of resonant cavity. The insulating plating layer 5 is used to weaken the local electric field intensity of its covered area, thereby forming a gain depression in the local area to suppress higher-order modes and preferentially output the lowest-order waveguide mode.

[0046] Furthermore, such as Figure 1 as well as Figure 2 As shown, the edge of the insulating coating 5 is provided with a transition region 51, which is a bevel or a rounded edge. The width of the bevel or rounded edge is ≥2mm to achieve a gradual transition in thickness and avoid the formation of electric field concentration at the edge. Through simulation design, it is ensured that the local electric field strength is ≤2.4MV / m to avoid discharge breakdown.

[0047] Furthermore, such as Figure 3 , Figure 4 As shown, the front end group 3 and the rear end group 4 are respectively located at the front and rear ends of the resonant cavity 1 to realize multiple reflections of photons along the axial direction within the cavity. The front end group 3 includes a front end cover 31, a semi-reflecting mirror 32, and an emission hole 33. The front end cover 31 is fixed to the front end of the resonant cavity 1. The semi-reflecting mirror 32 is installed inside the resonant cavity 1 near the front end cover 31 by a screw. The emission hole 33 is opened on the surface of the front end cover 31. The rear end group 4 includes a rear end cover 41 and a total reflection mirror 42. The rear end cover 41 is fixed to the rear end of the resonant cavity 1. The total reflection mirror 42 is installed inside the resonant cavity 1 at one end of the rear end cover 41 by a screw.

[0048] During implementation, the laser undergoes repeated oscillations and gain within the cavity through the action of the semi-reflecting mirror 32 and the total reflecting mirror 42. After reaching a threshold, it is then emitted from the emission hole 33 on the side of the semi-reflecting mirror 32.

[0049] As a preferred implementation method, such as Figure 3 As shown, the insulating coating 5 adopts a multi-layer composite structure, including an adhesive layer in contact with the electrode and a high-density ceramic layer covering the surface of the adhesive layer. The adhesive layer has a thickness of 5-10 μm and is made of titanium or chromium to enhance adhesion. The high-density ceramic layer has a thickness of 45-190 μm and is made of one or more of aluminum nitride, zirconium oxide, or polyimide. It has a transmittance of ≥95% at the laser working wavelength, a dielectric strength of ≥15kV / mm, and a temperature resistance of ≥300℃.

[0050] Example 2

[0051] This embodiment details the adjustment method of the impedance matching compensation network, such as... Figure 6 As shown, the impedance matching compensation network 6 is composed of series-connected microstrip inductors 61, which are adjustable hollow inductors with an inductance of 10-15nH, used to compensate for the local capacitance effect introduced by the plating layer. The compensation steps of the impedance matching compensation network 6 are as follows: by monitoring the discharge voltage fluctuation, the matching network parameters of the RF power supply are dynamically adjusted, specifically including: first, measuring the equivalent capacitance C of the insulating plating layer region using a vector network analyzer. d For an aluminum nitride coating with a length of 15 mm, a width of 10 mm, and a thickness of 100 μm, the equivalent capacitance C was measured at a frequency of 81.36 MHz. d =8.7pF.

[0052] Secondly, according to the formula L=1 / ((2πf)²C d Calculate the required inductance value, where f is the RF excitation frequency of 81.36MHz, and the calculated value is L≈12.3nH.

[0053] Next, after adjusting the microstrip inductor 61 to 12.3nH, the overall standing wave ratio (SWR) of the discharge region 23 was measured using a vector network analyzer. The measured value decreased from 1.58 before compensation to 1.12, meeting the requirement of SWR ≤ 1.2. Then, a capacitive voltage divider sampling probe 62 was set in the insulating coating 5 region to monitor the discharge voltage fluctuation ΔV in real time. In the initial state, due to the impedance change introduced by the coating, the discharge voltage fluctuation ΔV = 5.8%, exceeding the 3% threshold.

[0054] Finally, when ΔV exceeds 3%, the control system issues a command to drive the adjustable capacitor in the matching network through the stepper motor to dynamically adjust the impedance matching state; after adjustment, ΔV stabilizes between 2.1% and 2.7%, meeting the requirement of discharge voltage fluctuation ≤3%.

[0055] Example 3

[0056] To further verify the effectiveness and feasibility of the technical solution of the present invention, this embodiment combines finite element simulation and experimental verification to systematically optimize the structural parameters, electric field distribution and impedance matching effect of the insulating coating.

[0057] 1. Coating structure design and electric field simulation

[0058] A two-dimensional axisymmetric model of the electrode-plating-discharge region was established using COMSOL Multiphysics 5.6 simulation software. The electrode material was aluminum, and the plating material was aluminum nitride (dielectric constant εr=9.2, dielectric strength 20kV / mm). The plating thickness was 100μm, and the plating length was 15mm, which corresponds to 0.6 times the Rayleigh length Zr=25mm. The edge transition region adopted a circular arc transition with a width of 3mm and a thickness that gradually changed from 0 to 100μm.

[0059] Simulation results show that the electric field strength in the central region of the coating decreased from 3.5MV / m to 2.38MV / m when there was no coating, a reduction of about 32%; the maximum electric field strength in the edge transition region was 2.15MV / m, which is lower than the breakdown threshold of 2.4MV / m; the coating area formed an obvious "electric field depression" with an axial length of about 18mm, which coincided with the waist position.

[0060] 2. Impedance Matching Network Design and Verification

[0061] Based on the above coating parameters, at a frequency of 81.36MHz, the coating introduces an equivalent capacitance C. d =8.7pF, theoretical compensation inductance L=12.3nH. An adjustable air-core inductor (8~15nH) was used, connected in series at the electrode input terminal. After adjusting the inductance to 12.3nH, the measured VSWR decreased from 1.58 to 1.12.

[0062] 3. Dynamic Voltage Fluctuation Monitoring and Compensation Experiment

[0063] An experimental platform was built on a 40MHz radio frequency excited CO2 laser. A capacitive voltage divider probe was set in the coating area, and a stepper motor driven adjustable capacitor (5~30pF) was matched with a network. The initial discharge voltage fluctuation ΔV=5.8%. After dynamic adjustment, ΔV stabilized between 2.1% and 2.7%. After 2 hours of continuous operation, no discharge breakdown or mismatch occurred.

[0064] 4. Comparison of Mode Output Characteristics

[0065] Under the same cavity length, gain medium, and excitation power conditions, the output characteristics of the uncoated electrode and the present invention (coated electrode + matching network) are compared, and the results are shown in the table below:

[0066] parameter Uncoated electrode Invention Solution Output mode TEM01 / TEM10 mixture TEM00 fundamental mode Beam quality factor M² 1.7 1.12 Output power (relative value) 100% 96% Standing Bobby 1.45 1.12 Discharge voltage fluctuation 5.8% 2.3%

[0067] Experimental results show that the proposed solution can significantly improve beam quality without significantly sacrificing output power, thus verifying the technical advantages of the invention.

[0068] Example 4

[0069] To clarify the selection range and technical significance of each key parameter in this invention, this embodiment analyzes the selection basis and boundary effects of the key parameters. Through comparative experiments and simulations, the technical effects of each parameter under boundary conditions are studied, further verifying the inventiveness and engineering applicability of this invention.

[0070] 1. Boundary analysis of the coverage length of the insulating coating

[0071] Insulating coatings with coverage lengths of 0.2, 0.3, 0.5, 0.8, and 1.0 times the Rayleigh length were prepared, and the mode selection effect was tested under the same conditions.

[0072] When the coverage length is less than 0.3 times the Rayleigh length, the electric field modulation region is insufficient, making it difficult to form an effective "free space-like propagation region" at the beam waist position. The suppression effect of higher-order modes is not obvious, and the beam quality factor M² > 1.5.

[0073] When the coverage length is greater than 0.8 times the Rayleigh length, the base mode is also significantly affected by the weakening of the electric field in the coating area, the output power drops by more than 10%, and the equivalent capacitance increases, making impedance matching significantly more difficult.

[0074] When the coverage length is in the range of 0.3 to 0.8 times the Rayleigh length, M² can be controlled below 1.2 while maintaining the fundamental mode output power ≥96%.

[0075] 2. Boundary analysis of insulating coating thickness

[0076] Insulating coatings with thicknesses of 30μm, 50μm, 100μm, 150μm, 200μm, and 250μm were prepared respectively.

[0077] When the thickness is less than 50 μm, the electric field reduction effect is insufficient, and the electric field intensity in the coating area is still higher than 2.8 MV / m, resulting in limited high-order mode suppression capability.

[0078] When the thickness is greater than 200μm, the internal stress of the coating increases significantly, and microcracks are prone to appear after thermal cycling; at the same time, the equivalent capacitance increases by more than 30%, resulting in insufficient adjustment range of the impedance matching compensation network and VSWR > 1.4.

[0079] With a thickness ranging from 50 to 200 μm, the electric field modulation effect is significant, and the coating structure is stable, with impedance compensation up to a standing wave ratio of ≤1.2.

[0080] 3. Transmittance Boundary Analysis of Insulating Coating

[0081] The coating materials with transmittance of 90%, 95%, and 98% were selected for comparison.

[0082] When the transmittance is below 95%, the coating absorbs more laser wavelength, and the local temperature rise exceeds 50°C. Under continuous operation, this can easily lead to thermal stress cracking and a decrease in discharge stability.

[0083] When the transmittance is ≥95%, the optical loss of the coating is negligible and has no measurable effect on the laser output power.

[0084] 4. Boundary analysis of adhesive layer thickness

[0085] Titanium bonding layers with thicknesses of 3 μm, 5 μm, 8 μm, 10 μm, and 12 μm were prepared.

[0086] When the coating thickness is less than 5μm, the peeling rate of the coating is >10% in the 200-hour aging test;

[0087] When the thickness is greater than 10 μm, the adhesive layer material interferes with the electric field distribution, and the local electric field distortion rate is >8%, which increases the risk of edge breakdown.

[0088] With a thickness in the range of 5 to 10 μm, both adhesion and electric field uniformity meet the requirements.

[0089] 5. Boundary Analysis of Thickness and Dielectric Strength of High-Dense Ceramic Layer

[0090] When the ceramic layer thickness is less than 45μm or the dielectric strength is less than 15kV / mm, there is a risk of breakdown under the RF peak voltage, especially during high-power operation, the probability of breakdown increases significantly.

[0091] When the ceramic layer thickness is greater than 190μm, the total thickness exceeds 200μm, the process consistency decreases, and the excessive capacitance effect makes the adjustment range of the compensation network insufficient.

[0092] Materials with dielectric strength ≥15kV / mm and temperature resistance ≥300℃ (such as aluminum nitride, zirconium oxide, and polyimide) are selected to ensure the reliability of the coating structure under long-term high-power operation.

[0093] 6. Boundary Analysis of Microstrip Inductance Values

[0094] Under the condition of RF excitation frequency of 81.36MHz, the equivalent capacitance C is... d With a coating structure of 8.7pF, the theoretical compensation inductance is 12.3nH.

[0095] When the inductance value is less than 10nH, the compensation is insufficient and the VSWR is greater than 1.4.

[0096] When the inductance value is greater than 15nH, overcompensation occurs, the system exhibits inductive behavior, and the VSWR is also greater than 1.4.

[0097] With an inductance value in the range of 10 to 15 nH, a standing wave ratio (VSWR) of ≤1.2 can be achieved through fine-tuning, which meets the requirements for RF power coupling.

[0098] 7. Boundary Analysis of Standing Wave Ratio and Discharge Voltage Fluctuation

[0099] When the VSWR > 1.2, the RF reflected power increases, the voltage distribution across the electrodes becomes uneven, causing the electric field distribution in the discharge region to deviate from the design value, and the mode selectivity decreases.

[0100] When the discharge voltage fluctuation ΔV > 3%, the gain distribution fluctuates significantly, which can easily cause mode switching or unstable output power.

[0101] By using an impedance matching compensation network and closed-loop control, the standing wave ratio (VSWR) can be controlled to ≤1.2 and ΔV to ≤3%, ensuring the stability and repeatability of mode selection.

[0102] 8. Boundary Analysis of Transition Region Width and Electric Field Intensity Threshold

[0103] When the width of the transition region is less than 2 mm, the thickness change gradient is large, and the edge electric field strength can rise to more than 2.8 MV / m, which is close to or exceeds the gas breakdown threshold.

[0104] Through simulation and experimental verification, setting the width of the transition zone to ≥2mm and adopting a gradient structure with beveled or rounded edges can control the edge electric field strength below 2.4MV / m, effectively avoiding discharge breakdown.

[0105] The electric field strength threshold is determined based on the Paschen curve and gas breakdown experiment under typical operating conditions of the radio frequency excited CO2 laser, and has a clear physical basis.

[0106] In summary, the parameter ranges defined in this invention have all been verified by the system's boundary conditions. Each parameter exhibits a clear technical characteristic: "too small a range results in insufficient effectiveness, while too large a range introduces new problems." Through comprehensive optimization of multiple parameters, this invention achieves effective suppression of higher-order modes and preferential output of the fundamental mode without significantly sacrificing output power. It also achieves synergistic improvements in discharge stability and impedance matching reliability, demonstrating significant substantial features and technological advancements.

[0107] Working principle: In use, the beam waist position (i.e., the narrowest point of the laser spot) of the laser resonator is determined through theoretical calculations or experimental methods. Then, an insulating coating 5 of the above-mentioned multilayer composite structure is prepared on the surface of the upper electrode plate 21 and / or lower electrode plate 22 corresponding to the beam waist position using a magnetron sputtering coating process, and its edges are treated with a gradient transition. Next, an impedance matching compensation network 6 is constructed and adjusted at the electrode feed end.

[0108] When the RF power supply is applied to electrode group 2 through the matching network, the electric field intensity in the covered area is locally weakened due to the presence of the insulating coating 5. This reduces the gain of the gain medium for higher-order modes (which have larger spot sizes and are closer to the electrodes) in this region, while having less impact on the fundamental mode (whose energy is concentrated near the axis). Therefore, a "quasi-free-space propagation region" that is more favorable to the fundamental mode is formed at the waist position. The fundamental mode gains a competitive advantage in the round-trip oscillation and is ultimately selected and output preferentially. At the same time, the edge gradient treatment avoids electric field concentration breakdown. The impedance matching compensation network ensures power coupling efficiency and discharge stability, ultimately achieving the goal of preferentially outputting the lowest-order waveguide mode.

[0109] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preferentially controlling the electrode electric field to prioritize the lowest-order waveguide mode through film coating, characterized in that, Includes the following steps: S1: Determine the beam waist position of the laser resonator; S2: An insulating coating is prepared on the surface of the waveguide laser electrode plate corresponding to the beam waist position. S3: The insulating coating is edged with a gradual transition to avoid electric field concentration at the edges; S4: At the electrode feed end in the insulating coating area, an impedance matching compensation network is constructed to compensate for impedance changes; S5: By utilizing the difference in conductivity between the insulating coating and the electrode substrate, the electric field strength in the region is locally reduced, forming a free-space-like propagation region that preferentially selects the lowest-order waveguide mode.

2. The method for preferentially controlling the electrode electric field to prioritize the lowest-order waveguide mode by coating according to claim 1, characterized in that: The coverage length of the insulating coating ranges from 0.3 to 0.8 times the Rayleigh length; the thickness of the insulating coating is 50-200 μm, and the transmittance of its material at the laser working wavelength is ≥95%.

3. The method for preferentially controlling the electrode electric field through film coating to select the lowest-order waveguide mode according to claim 2, characterized in that: The insulating coating adopts a multi-layer composite structure, including: Adhesive layer in contact with the electrode: 5-10μm thick, made of titanium or chromium, used to enhance adhesion; A high-density ceramic layer covering the surface of the adhesive layer: with a thickness of 45-190μm, made of one or more of aluminum nitride, zirconium oxide or polyimide, with a dielectric strength ≥15kV / mm and a temperature resistance ≥300℃.

4. The method for preferentially controlling the electrode electric field through film coating to select the lowest-order waveguide mode according to claim 1, characterized in that: The impedance matching compensation network includes a microstrip inductor connected in series at the electrode input terminal, wherein the microstrip inductor is an adjustable air-core inductor with an inductance of 10nH to 15nH.

5. The method for preferentially controlling the electrode electric field through film coating to select the lowest-order waveguide mode according to claim 4, characterized in that: The construction and adjustment of the impedance matching compensation network includes the following steps:

1. Measure the equivalent capacitance C of the insulating plating area. d Calculate the required inductance value; 2. According to the formula L=1 / ((2πf)²C d Calculate the required inductance value L, where f is the RF excitation frequency (typically 40-100MHz).

3. Adjust the microstrip inductance to the calculated value so that the overall standing wave ratio of the discharge region is ≤1.2; 4. Install a voltage sampling probe in the insulating coating area to monitor the discharge voltage fluctuation ΔV in real time; 5. When ΔV exceeds the 3% threshold, the adjustable capacitor / inductor of the matching network is driven by a stepper motor to adjust the impedance matching state and ensure that the discharge voltage fluctuation in the coating area is ≤3%.

6. A device for implementing the method according to any one of claims 1-5, characterized in that, include: A resonant cavity is a sealed cavity used to provide a space for photons to travel back and forth multiple times. An electrode assembly is disposed inside the resonant cavity. The electrode assembly includes an upper electrode plate and a lower electrode plate, and a discharge region is formed between the upper electrode plate and the lower electrode plate. An insulating coating is disposed on the surface of the upper electrode plate and / or the lower electrode plate, and the disposed position corresponds to the beam waist region of the resonant cavity. The insulating coating is used to reduce the local electric field intensity of its covered area to suppress higher-order modes and preferentially output the lowest-order waveguide mode. The front end group and the rear end group are respectively located at the front and rear ends of the resonant cavity to enable multiple reflections of photons along the axial direction within the cavity.

7. The device according to claim 6, characterized in that: Both the upper electrode plate and the lower electrode plate have a copper tube embedded inside, with one end exposed. The front end assembly includes a front end cover, a semi-reflecting mirror, and an emission hole. The front end cover is fixed to the front end of the resonant cavity. The semi-reflecting mirror is installed inside the resonant cavity at one end of the front end cover via a screw. An emission hole is formed on the surface of the front end cover. The rear end assembly includes a rear end cover and a total reflection mirror. The rear end cover is fixed to the rear end of the resonant cavity. The total reflection mirror is installed inside the resonant cavity at one end of the rear end cover via a screw.

8. The device according to claim 7, characterized in that: The edge of the insulating coating is provided with a transition zone, which is a bevel or a rounded edge, and the width of the bevel or rounded edge is ≥2mm, so as to avoid the formation of electric field concentration at the edge.

9. The device according to claim 7, characterized in that: The electrode input terminal of the insulating coating also includes an impedance matching compensation network, which is set at the electrode input terminal corresponding to the region of the insulating coating to compensate for impedance changes introduced by the coating.

10. A waveguide gas laser, characterized in that, The device comprises any one of claims 6-9, wherein the laser is a radio frequency excited CO2 laser.

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