Waveguide mode structure based on conductive difference plating film

Abstract

This invention relates to the field of waveguide laser technology, comprising a pair of parallel, oppositely arranged electrode plates, spaced apart to form a waveguide gap; resonant cavities are provided at both ends of the two electrode plates along their length; an insulating coating is provided on the inner surface of at least one electrode plate corresponding to the beam waist region of the resonant cavity; the insulating coating is used to locally weaken the constraint of the electric field on this region by utilizing the difference in conductivity between itself and the electrode plates, forming a free-space-like propagation region with an electric field strength lower than the surrounding region, thereby preferentially selecting the lowest-order waveguide mode for propagation. This invention significantly improves the suppression capability of higher-order modes, avoids the processing difficulty and loss problems caused by excessively small gaps, significantly improves the long-term operational stability of the device, increases the laser damage resistance threshold by approximately 40%, and improves surface thermal conductivity by approximately 25%, thereby effectively extending the device's lifespan.

Description

Technical Field

[0001] This invention relates to the field of waveguide laser technology, specifically to waveguide mode structures based on conductive differential coatings. Background Technology

[0002] Slab waveguide lasers, as an important laser source, are widely used in industrial processing, medical aesthetics, military defense, and other fields. In slab waveguide lasers, the waveguide mode structure directly affects the beam quality and power stability of the laser output. Traditional waveguide mode structures typically use parallel electrode plates to form the waveguide gap, utilizing the constraint of the electric field by the electrode plates to guide laser propagation.

[0003] However, existing waveguide mode structures suffer from the following problems in practical applications: First, during waveguide propagation, higher-order modes coexist with the fundamental mode, leading to a decrease in output beam quality and affecting laser focusing performance and processing accuracy. Although reducing the waveguide gap can suppress higher-order modes to some extent, it also increases processing difficulty and losses. Second, the electric field distribution in traditional structures is relatively uniform, lacking the ability to control the electric field in specific regions, making it difficult to achieve precise selection of propagation modes. Furthermore, while some improved structures can suppress higher-order modes, they are often complex, difficult to debug, or introduce additional heat accumulation problems, affecting the long-term stability of the equipment. Therefore, there is an urgent need for a waveguide mode structure that can effectively suppress higher-order modes, improve beam quality, and is compact in structure. Summary of the Invention

[0004] The purpose of this invention is to provide a waveguide mode structure based on conductivity difference coating to solve the problems of difficulty in suppressing higher-order modes and poor beam quality in waveguide lasers mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a waveguide mode structure based on conductivity difference coating, comprising a pair of parallel and oppositely arranged electrode plates, the two electrode plates being spaced apart from each other to form a waveguide gap, the height of the waveguide gap being in the range of 1 mm to 4 mm; resonant cavities are provided at both ends of the two electrode plates along the length direction to form an optical propagation axis; an insulating coating is provided on the inner surface of at least one of the electrode plates corresponding to the beam waist region of the resonant cavity;

[0006] The insulating coating is used to locally reduce the constraint of the electric field on the region by utilizing the difference in conductivity between it and the electrode plate, forming a free-space-like propagation region with an electric field strength lower than that of the surrounding region, so as to preferentially select the lowest order waveguide mode for propagation.

[0007] Preferably, the resonant cavity is an unstable resonator capable of providing a forward wave mode and a reverse wave mode, wherein the reverse wave mode has a beam waist, and the resonant cavity is specifically a negative-braced unstable resonator; the center of the insulating coating is aligned with the center of the beam waist of the resonant cavity, with a deviation of no more than 0.5 mm.

[0008] Preferably, the insulating coating has a coverage length of 0.3 to 0.8 times the Rayleigh length along the light propagation direction; and the thickness of the insulating coating is 50 to 200 μm.

[0009] Preferably, the insulating coating covers a width of 1 / 2 to the entire reverse wave mode of the resonant cavity; the insulating coating is made of one or more of aluminum nitride, zirconium oxide, or polyimide.

[0010] Preferably, the electrode plate is embedded with a multi-dimensional flow channel cooling structure. The flow channel density of this cooling structure on the back side corresponding to the insulating coating is higher than that in other areas of the electrode plate, in order to compensate for the additional heat accumulation introduced by the coating.

[0011] Preferably, a gradient transition structure is provided at the edge of the insulating coating to avoid electric field concentration at the edge; the gradient transition structure is a beveled transition section or a circular arc transition section, the radius of curvature R of the circular arc transition section is ≥5mm, the width of its transition region is not less than 2mm, and the local electric field strength is not greater than 2.4MV / m, and the transition region is covered with a gradient-doped semiconductor buffer layer to further smooth impedance abrupt changes.

[0012] Preferably, there are two electrode plates, and the inner surfaces of both electrode plates are provided with the insulating coating to form a symmetrical layout. The insulating coating only covers a local area of ​​the inner surface of the electrode plate, rather than the entire surface.

[0013] Preferably, the insulating coating is attached to the inner surface of the electrode plate by a vacuum coating process, wherein the vacuum coating process is magnetron sputtering; its transmittance of CO2 laser at a wavelength of 10.6μm is ≥95%, and its surface roughness Ra≤0.8μm to reduce waveguide loss, its dielectric strength is not less than 15kV / mm, and its temperature resistance is not less than 300℃.

[0014] Preferably, the inner surface of the electrode plate is provided with a high-reflectivity metal film layer in the area where no insulating coating is provided, with a reflectivity of not less than 98%, to enhance the suppression of higher-order modes and form a "conductive-insulating-high reflectivity" composite interface with the insulating coating; the surface of the insulating coating is also covered with a layer of graphene or diamond-like carbon film with a thickness of 5 nm to 50 nm to improve the laser damage threshold and enhance the surface thermal conductivity.

[0015] The present invention also provides a slab waveguide laser, comprising the waveguide mode structure based on conductivity difference coating as described in any of the preceding claims.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention significantly improves the suppression capability of higher-order modes. By creating a difference in conductivity between the insulating coating and the electrode plate, the electric field constraint is locally weakened in the beam waist region, forming a free-space-like propagation region. Experimental results show that compared with the traditional uncoated structure, this invention improves the suppression ratio of higher-order modes by approximately 3.2 times, increases the fundamental mode transmission efficiency to over 92%, and improves the output beam quality factor M. 2 It decreased from the original 3.5 to below 1.3, approaching the diffraction limit.

[0018] This invention improves mode selection accuracy and structural integration by precisely matching the coverage length, thickness, and position of the insulating coating with the beam waist of the resonant cavity. The coverage length is 0.3 to 0.8 times the Rayleigh length, and the position deviation is controlled within ≤0.5mm. Compared with the traditional mode selection method that relies on waveguide gap compression, this invention achieves an improvement of approximately 2.8 times in high-order mode suppression ratio without reducing the waveguide gap, avoiding the processing difficulty and loss problems caused by excessively small gaps.

[0019] This invention optimizes thermal management and electric field concentration. By setting a multi-dimensional flow channel cooling structure inside the electrode plate and increasing the flow channel density in the back region of the insulating coating (by 30% to 50% compared to other regions), it effectively compensates for the additional heat accumulation introduced by the coating. Combined with an edge gradient transition structure (circular arc transition curvature radius ≥ 5 mm, transition width ≥ 2 mm) and a gradient-doped semiconductor buffer layer, the local electric field intensity is controlled at ≤ 2.4 MV / m. Compared with traditional structures, the edge electric field concentration is reduced by about 60%, significantly improving the long-term stability of the equipment.

[0020] This invention enhances mode selection and damage resistance by introducing a high-reflectivity metal film (reflectivity ≥98%) in areas without an insulating coating. This film forms a "conductive-insulating-high-reflectivity" composite interface with the insulating coating, further enhancing the suppression of higher-order modes and increasing the higher-order mode loss coefficient to ≥0.85cm. -1 The nanoscale graphene or diamond-like carbon film (5nm~50nm thick) covering the insulating coating increases the laser damage resistance threshold by about 40% and the surface thermal conductivity by about 25%, effectively extending the device's lifespan. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0022] Figure 2This is a schematic diagram of the exploded structure of the present invention;

[0023] Figure 3 This is a schematic diagram of the resonant cavity structure of the present invention;

[0024] Figure 4 This is a schematic diagram of the multi-dimensional flow channel cooling structure of the present invention;

[0025] Figure 5 This is a schematic diagram of the dielectric grid array structure of the present invention.

[0026] In the figure: 1. Electrode plate; 2. Waveguide gap; 3. Insulating coating; 4. Gradual transition structure; 5. Resonant cavity; 6. Multi-dimensional flow channel cooling structure; 7. High reflectivity metal film layer; 8. Dielectric grid array. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. In addition, the terms "first," "second," "third," "upper," "lower," "left," "right," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. At the same time, in the description of the present invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The waveguide mode structure based on conductivity difference coating provided by this invention is as follows: Figure 1 and Figure 2 As shown, it includes a pair of parallel and oppositely arranged electrode plates 1, with the two electrode plates 1 spaced apart from each other to form a waveguide gap 2 between them. The height of the waveguide gap 2 ranges from 1 mm to 4 mm. Resonant cavities 5 are provided at both ends of the two electrode plates 1 along the length direction to form the light propagation axis. An insulating coating layer 3 is provided on the inner surface of at least one electrode plate 1 corresponding to the beam waist region of the resonant cavity 5.

[0029] An interface with a conductivity difference is formed between the insulating coating 3 and the electrode plate 1. This interface is used to locally reduce the constraint of the electric field on this region, creating a free-space-like propagation region with a lower electric field strength than the surrounding area. This allows the lowest-order waveguide mode to be preferentially selected for propagation. The free-space-like propagation region refers to a region where, due to the presence of the insulating coating, the electric field strength is reduced by at least 30% compared to the electrode plate region without the insulating coating. This significantly increases the propagation loss of higher-order modes, while the propagation of the lowest-order waveguide mode remains largely unaffected.

[0030] Example 1

[0031] In this embodiment, as Figure 2 and Figure 3 As shown, the resonant cavity 5 is an unstable resonator capable of providing both a forward wave mode and a reverse wave mode. The reverse wave mode has a beam waist. Specifically, the resonant cavity 5 is a negative-branch unstable resonator. The resonant cavity 5 includes a total reflection mirror and an output mirror, and an emission hole is provided on the output mirror side. During implementation, the laser repeatedly oscillates between the total reflection mirror and the output mirror to achieve a gain. After reaching a threshold, it is emitted from the emission hole on the output mirror side. The center of the insulating coating 3 is aligned with the center of the beam waist of the resonant cavity 5, with a deviation of no more than 0.5 mm. The insulating coating 3 is attached to the inner surface of the electrode plate 1 by a vacuum coating process, which is magnetron sputtering. Its transmittance of CO2 laser at a wavelength of 10.6 μm is ≥95%, and its surface roughness Ra≤0.8 μm to reduce waveguide loss. Its dielectric strength is not less than 15 kV / mm, and its temperature resistance is not less than 300℃.

[0032] There are two electrode plates 1, and the inner surfaces of both electrode plates 1 are provided with insulating coatings 3, forming a symmetrical layout. The insulating coatings 3 only cover a local area of ​​the inner surface of the electrode plates 1, rather than the entire surface. The insulating coatings 3 are made of one or more of aluminum nitride, zirconium oxide, or polyimide. The coverage length of the insulating coatings 3 along the light propagation direction is 0.3 to 0.8 times the Rayleigh length. The thickness of the insulating coatings 3 is 50 to 200 μm. The coverage width of the insulating coatings 3 is 1 / 2 to the entire reverse wave mode of the resonant cavity 5.

[0033] In this embodiment, taking a CO2 laser (wavelength 10.6μm) as an example, under the conditions of a waveguide gap of 2mm and a non-stable negative branch cavity, an insulating coating (aluminum nitride material, thickness 100μm, coverage length of 0.5 times Rayleigh length, and width of the full width of the reverse wave mode) is set.

[0034] Test results show that the fundamental mode transmission loss is 0.08 dB / m, and the higher-order mode loss is 0.65 dB / m.

[0035] Compared to traditional uncoated structures, the higher-order mode loss is increased by approximately 4.1 times, while the fundamental mode transmission loss increases by only 0.02 dB / m; the output beam M2 The beam quality was significantly improved by reducing the beam strength from 3.2 to 1.2.

[0036] Example 2

[0037] This embodiment is based on Embodiment 1, such as... Figure 4 As shown, a multi-dimensional flow channel cooling structure 6 is embedded inside the electrode plate 1. The flow channel density of this multi-dimensional flow channel cooling structure 6 on the back side corresponding to the insulating plating layer 3 is higher than the flow channel density in other areas of the electrode plate 1, in order to compensate for the additional heat accumulation introduced by the plating layer. Figure 2 As shown, a gradient transition structure 4 is provided at the edge of the insulating plating layer 3. The gradient transition structure 4 is used to avoid the concentration of electric field at the edge. The gradient transition structure 4 is a beveled transition part or a circular arc transition part. The circular arc transition part has a radius of curvature R≥5mm, a transition region width of not less than 2mm, and a local electric field strength of not more than 2.4MV / m. The transition region is covered with a gradient-doped semiconductor buffer layer to further smooth the impedance change.

[0038] In this embodiment, under the same laser power (2kW) continuous operation conditions: without cooling structure optimization, the temperature rise of the insulating coating area reaches 85℃, and the peak local electric field strength reaches 3.8MV / m; after adopting a multi-dimensional flow channel cooling structure (the flow channel density on the back of the coating increases by 40%) and combining it with a gradient transition structure, the temperature rise of the coating area drops to 38℃, and the peak electric field strength drops to 2.1MV / m; the continuous operation time of the equipment is extended from 2 hours to more than 10 hours, and no breakdown or degradation phenomenon occurs.

[0039] Example 3

[0040] This embodiment is based on Embodiment 1, such as... Figure 5 As shown, in the area where the insulating coating 3 is not provided, a high-reflectivity metal film layer 7 is also provided on the inner surface of the electrode plate 1. The reflectivity is not less than 98%, which is used to enhance the suppression of higher-order modes and form a "conductive-insulating-high reflectivity" composite interface with the insulating coating 3. The surface of the insulating coating 3 is also covered with a layer of graphene or diamond-like carbon film with a thickness of 10 nm, which is used to improve the laser damage threshold and enhance the surface thermal conductivity. The thickness of the film is 5 nm to 50 nm.

[0041] In this embodiment, test results show that the laser damage resistance threshold is reduced from 0.8 J / cm². 2 Increased to 1.15 J / cm 2 The surface thermal conductivity was increased from 1.2 W / m·K to 1.5 W / m·K; the transmittance at a wavelength of 10.6 μm remained above 96%, without affecting the mode selection performance.

[0042] In addition, the insulating coating 3 in this embodiment is a discontinuously distributed insulating ceramic coating 3. The coverage width of the insulating coating 3 is asymmetrically distributed along the light propagation direction, wherein the coverage width near the output mirror side is greater than the coverage width near the total reflection mirror side. At least one layer of dielectric grating array 8 is also provided in the waveguide gap 2 between the two electrode plates 1. The dielectric grating array 8 is periodically arranged along the light propagation direction to further suppress the propagation of asymmetric modes while maintaining the transmission of the fundamental mode.

[0043] This structure maintains fundamental mode transmission while further suppressing the propagation of asymmetric modes. Experiments show that the asymmetric mode suppression ratio is improved by about 2.5 times, while the fundamental mode transmission efficiency remains above 90%.

[0044] To more intuitively demonstrate the technical effects of this invention, the following table summarizes the key performance comparison data with traditional uncoated structures:

[0045] Performance indicators Traditional uncoated structure Structure of the present invention Higher-order mode suppression ratio 1.0 (Baseline) 3.2 times Fundamental mode transmission efficiency Approximately 75% ≥92% <![CDATA[Output beam quality factor M 2 > 3.5 ≤1.3 Higher-order mode loss coefficient <![CDATA[Approximately 0.20 cm -1 > <![CDATA[≥0.85cm -1 <!-- 4 -->]]> Temperature rise in the coating area (2kW continuous operation) 85℃ (no optimization) ≤38℃ (cooling + gradient structure) Peak local electric field intensity 3.8MV / m ≤2.1MV / m Continuous stable operation time Approximately 2 hours ≥10 hours Laser damage threshold 0.8J / cm² ≥1.15J / cm² Surface thermal conductivity 1.2W / m·K ≥1.5W / m·K

[0046] The test conditions in the table above are as follows: Test wavelength: 10.6 μm (CO2 laser); Resonant cavity type: negative-branch unstable cavity; Waveguide gap: 2.0 mm; Insulating coating material: aluminum nitride (AlN); Thickness: 100 μm; Coverage length: 0.5 times Rayleigh length; Test power: continuous output 2 kW; Cooling water temperature: 20℃±1℃; Ambient temperature: 25℃±2℃; Electric field strength test: RF excitation frequency 13.56 MHz, combined with simulation and actual measurement with a high-voltage probe; Beam quality factor M 2 The beam quality analyzer was used for measurement, and the higher-order mode loss coefficient was determined by cavity ring-down spectroscopy (CRDS). The laser damage resistance threshold was tested according to ISO 21254 standard, and the surface thermal conductivity was measured by transient thermal reflection (TTR) method.

[0047] Example 4

[0048] To clarify the selection range and technical significance of each key parameter in this invention, and to verify the applicability of the technical solution of this invention, tests were also conducted within different parameter ranges:

[0049] Insulating coatings with coverage lengths of 0.2, 0.3, 0.5, 0.8, and 1.0 times the Rayleigh length were prepared, and their effect on mode selection was tested. The results show that when the coverage length is in the range of 0.3 to 0.8 times the Rayleigh length, higher-order modes can be effectively suppressed while maintaining the fundamental mode output. When the coverage length is less than 0.3 times, the mode selection effect is not significant. When the coverage length is greater than 0.8 times, the fundamental mode loss increases, and the output power decreases significantly.

[0050] Insulating coatings with thicknesses of 30 μm, 50 μm, 100 μm, 150 μm, 200 μm, and 250 μm were prepared. The results showed that when the thickness was in the range of 50–200 μm, the electric field modulation effect was significant and the coating structure was stable; when the thickness was less than 50 μm, the electric field weakening effect was insufficient; when the thickness was greater than 200 μm, the internal stress of the coating increased, making it prone to cracking, and the excessive capacitance effect made matching difficult.

[0051] Aluminum nitride, zirconium oxide, and polyimide were used as high-density ceramic layer materials for different coating materials. All three materials met the requirements of transmittance ≥95%, dielectric strength ≥15kV / mm, and temperature resistance ≥300℃, thus achieving the technical effects of this invention. Aluminum nitride exhibits the best thermal conductivity, making it suitable for high-power operation; polyimide has the simplest processing method, making it suitable for low-cost applications.

[0052] The present invention also provides a slab waveguide laser, including the waveguide mode structure based on the above-described conductive difference coating.

[0053] Working principle: When the laser propagates in the waveguide gap 2, the electrode plate 1 has a constraining effect on the electric field, forming a waveguide effect. In the area where the insulating coating 3 is not set, the conductive surface of the electrode plate 1 maintains a strong electric field constraint, allowing multiple waveguide modes to coexist.

[0054] In the region corresponding to the beam waist of the resonant cavity 5, the conductivity of the electrode plate 1 surface is significantly reduced due to the presence of the insulating coating 3. The conductivity difference between the insulating coating 3 and the electrode plate 1 weakens the ability of this region to confine the electric field, forming a free-space propagation region where the local electric field strength is lower than that of the surrounding region.

[0055] According to waveguide theory, higher-order modes are more sensitive to changes in electric field constraint. In the free-space region where electric field constraint weakens, the propagation loss of higher-order modes increases significantly, while the lowest-order mode (fundamental mode) is less affected because its field distribution is more concentrated at the waveguide center, and it can pass through this region smoothly and continue propagating. Therefore, by reasonably setting the position, length, and width of the insulating coating 3, the fundamental mode can pass through preferentially, while higher-order modes are effectively suppressed, thereby achieving selective propagation of waveguide modes.

[0056] Meanwhile, the center of the insulating coating 3 is precisely aligned with the beam waist center of the resonant cavity 5, ensuring that the free-space-like region coincides with the beam waist position, further enhancing the mode selection effect on the fundamental mode. The coverage length of the insulating coating 3 is set to 0.3 to 0.8 times the Rayleigh length, which can effectively suppress higher-order modes while avoiding excessive influence on the propagation of the fundamental mode.

[0057] Inside the electrode plate 1, the multi-dimensional flow channel cooling structure has a higher flow channel density in the back area of ​​the insulating coating 3 than in other areas, which can effectively compensate for the additional heat accumulation introduced by the coating and ensure the stable operation of the equipment for a long time.

[0058] The gradient transition structure 4 set at the edge of the insulating coating 3 avoids the concentration of the edge electric field and prevents the risk of partial discharge and breakdown by using the bevel or arc transition and the gradient doped semiconductor buffer layer.

[0059] In addition, a high-reflectivity metal film layer with a reflectivity of not less than 98% is provided on the inner surface of the electrode plate 1 where the insulating coating 3 is not provided, further enhancing the ability to suppress higher-order modes. The nanoscale graphene or diamond-like carbon film covering the surface of the insulating coating 3 improves the laser damage threshold and surface thermal conductivity.

[0060] 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 waveguide mode structure based on conductivity difference coating, comprising a pair of parallel and oppositely arranged electrode plates, characterized in that: The two electrode plates are arranged opposite each other and spaced apart, forming a waveguide gap between them. The height of the waveguide gap ranges from 1 mm to 4 mm. Resonant cavities are provided at both ends of the two electrode plates along the length direction to form the light propagation axis. An insulating coating is provided on the inner surface of at least one of the electrode plates corresponding to the beam waist region of the resonant cavity. The insulating coating is used to locally reduce the constraint of the electric field on the region by utilizing the difference in conductivity between it and the electrode plate, forming a free-space-like propagation region with an electric field strength lower than that of the surrounding region, so as to preferentially select the lowest order waveguide mode for propagation.

2. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The resonant cavity is an unstable resonator capable of providing a forward wave mode and a reverse wave mode, wherein the reverse wave mode has a beam waist, and the resonant cavity is specifically a negative-braced unstable resonator; the center of the insulating coating is aligned with the center of the beam waist of the resonant cavity, with a deviation of no more than 0.5 mm.

3. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The insulating coating has a coverage length of 0.3 to 0.8 times the Rayleigh length along the light propagation direction; the thickness of the insulating coating is 50 to 200 μm.

4. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The insulating coating covers a width of 1 / 2 to the entire reverse wave mode of the resonant cavity; the insulating coating is made of one or more of aluminum nitride, zirconium oxide, or polyimide.

5. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The electrode plate is embedded with a multi-dimensional flow channel cooling structure. The flow channel density of this cooling structure on the back side corresponding to the insulating coating is higher than that in other areas of the electrode plate, in order to compensate for the additional heat accumulation introduced by the coating.

6. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The edge of the insulating coating is provided with a gradient transition structure to avoid the concentration of electric field at the edge. The gradient transition structure is a beveled transition section or a circular arc transition section. The radius of curvature R of the circular arc transition section is ≥5mm, the width of its transition region is not less than 2mm, and the local electric field strength is not greater than 2.4MV / m. The transition region is covered with a gradient-doped semiconductor buffer layer to further smooth the impedance abrupt change.

7. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The insulating coating is attached to the inner surface of the electrode plate by a vacuum coating process, which is magnetron sputtering. The coating has a CO2 laser transmittance of ≥95% at a wavelength of 10.6μm and a surface roughness Ra≤0.8μm to reduce waveguide loss. The dielectric strength is not less than 15kV / mm and the temperature resistance is not less than 300℃.

8. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: The inner surface of the electrode plate is provided with a high-reflectivity metal film layer in the area where no insulating coating is provided. The reflectivity is not less than 98%, which is used to enhance the suppression of higher-order modes and form a "conductive-insulating-high reflectivity" composite interface with the insulating coating. The surface of the insulating coating is also covered with a layer of graphene or diamond-like carbon film with a thickness of 5 nm to 50 nm, which is used to improve the laser damage threshold and enhance the surface thermal conductivity.

9. The waveguide mode structure based on conductivity difference coating according to claim 1, characterized in that: At least one layer of dielectric grating array is also provided in the waveguide gap between the two electrode plates. The dielectric grating array is arranged periodically along the light propagation direction to further suppress the propagation of asymmetric modes while maintaining the transmission of the fundamental mode.

10. A slab waveguide laser, characterized in that, Including the waveguide mode structure based on conductivity difference coating as described in any one of claims 1 to 9.

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