Long-wave infrared laser reflector with three-medium structure

Abstract

The invention provides a long-wave infrared laser reflector with a three-medium structure. The long-wave infrared laser reflector structurally comprises a substrate Sub, a transition layer B, a metal layer G, a medium film system C and an air layer A from bottom to top. The dielectric film system C is structurally characterized by being formed by alternately stacking one or more groups of materials with high, medium and low refractive indexes. The invention aims to realize high reflection of a long-wave infrared band. Through meticulous design, three kinds of materials with high, medium and low refractive indexes are reasonably distributed in the reflector. According to the strategy, the absorption of the reflector is effectively reduced by balancing the low absorption of the chalcogenide and the low refractive index of the fluoride, the temperature rise caused by heat absorption is remarkably reduced, and meanwhile, the reflectivity is improved. Therefore, the continuous laser damage threshold value of the reflecting mirror is greatly enhanced theoretically, and the reflecting mirror shows higher stability and tolerance when facing continuous laser irradiation.

Description

Technical Field

[0001] This invention relates to the field of laser technology, specifically a long-wave infrared laser reflector with a three-medium structure, belonging to the field of thin-film optics technology. Background Technology

[0002] Long-wave infrared laser reflectors are crucial for laser transmission, applied both inside and outside the laser tube to promote laser oscillation, shorten tube length, optimize optical path, and improve design efficiency and laser performance. They are typically coated with metal or dielectric films. In radio frequency slab lasers, the reflector is paired with electrodes to form a gain region, where the laser is cyclically amplified to achieve a stable output.

[0003] Currently, the fabrication of long-wavelength infrared laser reflectors primarily employs processes such as single-metal coating, pure dielectric coating, or traditional molybdenum mirror polishing. However, with technological advancements, research into optimizing reflector performance is continuously deepening. For example, patent application (CN111505753A) discloses a carbon dioxide laser reflective film based on a silicon carbide substrate. This film system, through a multi-layer structure design, includes a silicon carbide substrate layer, a diamond-like carbon film layer, a nickel-chromium alloy bonding layer, a metal film, and alternating Ge and ZnS layers, as well as alternating YbF3 and ZnSe layers, achieving a reflectivity of 99.8% in the far-infrared 10.6μm band. Patent application (CN115508930A) explores a method for fabricating infrared high-reflectivity films. This film system, through the stacking of gold films and alternating ZnS and Ge dielectric films, achieves an average reflectivity of over 99.7% in the 3–5μm wavelength range. Patent application (CN116413844A) proposes an innovative design for a carbon dioxide laser reflector. This reflector consists of a silicon substrate, a nickel-chromium alloy transition layer, a metallic silver reflective layer, alternating ZnS and Ge layers, and an outer boron carbide layer. By precisely controlling the thickness of each layer, the reflector achieves an average reflectivity of over 99.5% in the 8-12 μm long-wavelength range. These patents significantly improve the reflectivity of long-wavelength infrared laser reflectors by layering high- and low-refractive-index dielectric layers on a metal film; however, their reflection effect is still limited, failing to fully achieve the 99.9% reflectivity standard under extreme environments. Particularly in continuous laser applications, the significant temperature rise caused by excessive absorption leads to a decrease in the reflector's damage threshold. Summary of the Invention

[0004] To address the shortcomings of existing technologies in terms of reflectivity, and considering the generally low absorption of chalcogenides and the relatively low refractive index of fluorides, this invention proposes a long-wave infrared laser reflector with a three-medium structure. This reflector aims to effectively reduce laser absorption by cleverly combining the low absorption characteristics of chalcogenides and the low refractive index of fluorides, while significantly improving laser reflectivity, thereby reducing the temperature rise effect of the reflector.

[0005] The technical solution provided by this invention is as follows:

[0006] An infrared laser reflector with a three-medium structure is proposed. The structure, from bottom to top, includes a substrate Sub, a transition layer B, a metal layer G, a dielectric film system C, and an air layer A. The dielectric film system C is formed by alternating deposition of one or more dielectric materials with high, medium, and low refractive indices, and the design is optimized based on the initial film system structure. The most important feature of the structure is that the dielectric film system C has the structure (xLyMzH)^n, where L is a low refractive index material with an optical thickness of λ / 4, M is a medium refractive index material with an optical thickness of λ / 4, H is a high refractive index material with an optical thickness of λ / 4, n is the number of periods, and x, y, and z are the film thickness coefficients of the low refractive index, medium refractive index, and high refractive index materials, respectively.

[0007] The number of periods n of the dielectric film is 1-10, and the film thickness coefficients x, y, and z of the low-refractive-index, medium-refractive-index, and high-refractive-index materials are between 0.1 and 3.

[0008] The substrate material is Cu, Mo, Ge, Si, chalcogenide glass, ZnSe, or ZnS.

[0009] The transition layer material is Cr or a chromium-nickel alloy.

[0010] The metal layer material is Au, Ag, or Al.

[0011] The high refractive index medium material is Ge or PbTe.

[0012] The medium refractive index material is ZnSe or ZnS.

[0013] The low-refractive-index medium material is BaF2, YF3, or YbF3.

[0014] Compared with the prior art, the technical effects of this invention are as follows:

[0015] 1. In the design process, compared with the traditional design that only uses two media materials, this invention innovatively introduces three materials with high, medium and low refractive indices. By optimizing the thickness of each layer of material through Macleod, the reflective film forms a stronger interference effect in a specific infrared wavelength range, thereby improving the reflectivity.

[0016] 2. This strategy, by balancing the low absorption of chalcogenide materials and the low refractive index of fluoride materials, significantly reduces the absorption of the mirror film and increases reflectivity, thereby reducing the temperature rise caused by heat absorption. Theoretically, this improvement greatly enhances the damage threshold of the mirror, enabling it to exhibit greater resistance to high-energy lasers. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a three-medium structure long-wave infrared laser reflector according to the present invention.

[0019] Figure 2 This is the final membrane structure of Example 1.

[0020] Figure 3 This is the final membrane structure of Example 2.

[0021] Figure 4 This is the final membrane structure of Example 3.

[0022] Figure 5 The reflectance spectrum curves of the film system in Example 1 in the range of 6-16 μm are shown.

[0023] Figure 6 The reflectance spectrum curves of the film system in Example 2 in the range of 5-15 μm are shown.

[0024] Figure 7 The reflectance spectrum curves of the film system in Example 3 in the range of 5-15 μm are shown. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] The high-reflectivity coating design requirements for Example 1 are: reflectivity >99.9% at 10.6μm and absorption less than or equal to 0.1%.

[0027] The design steps are as follows:

[0028] 1. The initial film structure, from bottom to top, consists of a substrate (Sub), a transition layer (B), a metal layer (G), a dielectric film (C), and an air layer (A). The dielectric film C has the structure (xLyMzH)^n. The substrate (Sub) is made of Cu, the transition layer is made of 20nm Cr, the metal layer (B) is made of 150nm Au, the high-refractive-index material (H) with an optical thickness of λ / 4 is Ge, the medium-refractive-index material (M) with an optical thickness of λ / 4 is ZnSe, and the low-refractive-index material (L) with an optical thickness of λ / 4 is YbF3. The film thickness coefficients x, y, and z are all chosen to be 0.66, and the number of periods is 3.

[0029] 2. The optimization target is set as a reflectivity of ≥99.9% and an absorption of ≤0.1% at 10.6µm.

[0030] 3. Preferably, the Cr layer and Au layer are deposited by magnetron sputtering, the Ge layer and YbF3 are deposited by electron beam heating evaporation, and the ZnSe layer is deposited by resistance heating evaporation.

[0031] 4. Optimization yields the best design result. The optimal membrane structure is as follows: Figure 2 As shown, the specific composition is sub / B0.72G0.70L0.19M1H0.38L0.50M0.98H0.21L0.73M0.97H / A, with a total thickness of 5.85μm and a total of 11 layers. The reflectivity is between 6-16μm. Figure 5 As shown, the reflectivity at 10.6 μm is as high as 99.95%.

[0032] Comparative Example 1: The only difference between this comparative example and Example 1 is that the dielectric film system C lacks the medium refractive index material ZnSe, that is, it only uses the high refractive index material Ge and the low refractive index material YbF3.

[0033] Comparative Example 2: The only difference between this comparative example and Example 1 is that the dielectric film system C lacks the high refractive index material Ge, that is, it only uses the medium refractive index material ZnSe and the low refractive index material YbF3.

[0034] Comparative Example 3: The only difference between this comparative example and Example 1 is that the dielectric film system C lacks the low refractive index material YbF3, that is, it only uses the high refractive index material Ge and the medium refractive index material ZnSe.

[0035] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 10.6µm reflectance 99.95％ 99.91％ 99.62％ 99.92％ 10.6µm absorption rate 0.05％ 0.09％ 0.38％ 0.08％

[0036] Table 1: Comparison of reflectance and absorptivity between Example 1 and Comparative Examples 1-3

[0037] By comparing Example 1 with the comparative example, we found that, while maintaining a consistent optical thickness, the three-medium structure reflective film composed of high, medium, and low refractive index materials exhibits significantly better reflective performance than the reflective film using only any two materials. Simultaneously, its absorptivity is also significantly lower than the latter. Particularly in the long-wave infrared band, absorbed laser energy is converted into heat, increasing the risk of film damage. Taking Comparative Example 3, which has the lowest absorptivity, as an example, it absorbs 60% more heat than Example 1, further highlighting the superiority of the three-medium structure reflective film in Example 1.

[0038] The high-reflectivity coating design requirements for Example 2 are: reflectivity greater than or equal to 99.9% at 9.3 μm and absorption less than or equal to 0.1%.

[0039] The design steps are as follows:

[0040] 1. The initial film structure, from bottom to top, consists of a substrate (Sub), a transition layer (B), a metal layer (G), a dielectric film (C), and an air layer (A). The dielectric film C has the structure (xLyMzH)^n. The substrate (Sub) is made of Si, the transition layer is 20nm Cr, the metal layer (B) is 150nm Ag, the high-refractive-index material (H) with an optical thickness of λ / 4 is Ge, the medium-refractive-index material (M) with an optical thickness of λ / 4 is ZnS, and the low-refractive-index material (L) with an optical thickness of λ / 4 is YF3. The film thickness coefficients x, y, and z are all chosen to be 0.66, and the number of periods is 3.

[0041] 2. The optimization target is set as a reflectivity of 9.3µm greater than or equal to 99.9% and an absorption of less than or equal to 0.1%.

[0042] 3. Preferably, the Cr layer and the Ag layer are deposited by magnetron sputtering, the Ge layer and YF3 are deposited by electron beam heating evaporation, and the ZnS layer is deposited by resistance heating evaporation.

[0043] 4. Optimization yields the best design result. The optimal membrane structure is as follows: Figure 3 As shown, the specific structure is sub / B0.72G0.83L0.17M1.01H0.53L0.25M1.03H0.38L0.41M1.04H / A, with a total thickness of 5.64μm and a total of 11 layers. The reflectivity in the 5-15μm range is as follows... Figure 6 As shown, the reflectivity at 9.3 μm is as high as 99.94%, and the absorption is less than 0.06%.

[0044] The high-reflectivity coating design requirements for Example 3 are: reflectivity greater than or equal to 99.9% at 9.3 μm and absorption less than or equal to 0.1%.

[0045] The design steps are as follows:

[0046] 1. The initial film structure, from bottom to top, consists of a substrate (Sub), a transition layer (B), a metal layer (G), a dielectric film system (C), and an air layer (A). The dielectric film system C has the structure (xLyMzH)^n. The substrate (Sub) is made of Mo, the transition layer is a 20nm chromium-nickel alloy, the metal layer (B) is made of 150nm Al, the high-refractive-index material (H) with an optical thickness of λ / 4 is Ge, the medium-refractive-index material (M) with an optical thickness of λ / 4 is ZnS, and the low-refractive-index material (L) with an optical thickness of λ / 4 is BaF2. The film thickness coefficients x, y, and z are all chosen to be 0.66, and the number of periods is 2.

[0047] 2. The optimization target is set as a reflectivity of 9.3µm greater than or equal to 99.9% and an absorption of less than or equal to 0.1%.

[0048] 3. Preferably, the chromium-nickel alloy layer and the Al layer are deposited by magnetron sputtering, the Ge layer and BaF2 are deposited by electron beam heating evaporation, and the ZnS layer is deposited by resistance heating evaporation.

[0049] 4. Optimization yields the best design result. The optimal membrane structure is as follows: Figure 4 As shown, the specific structure is sub / B0.96G0.84L0.08M1.01H0.56L0.23M1.05H / A, with a total thickness of 4.04μm and a total of 8 layers. The reflectivity is between 5-15μm. Figure 7 As shown, the reflectivity at 9.3 μm is as high as 99.93%, and the absorption is less than 0.07%.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A long-wave infrared laser reflector with a three-dielectric structure, characterized in that, The mirror consists of a substrate Sub, a transition layer B, a metal layer G, a dielectric film system C, and an air layer A from bottom to top. The dielectric film system C is formed by alternating deposition of one or more dielectric materials with high, medium, and low refractive indices, and the design is optimized based on the initial film system structure. The dielectric film system C has the structure (xLyMzH)^n, where L is a low-refractive-index material with an optical thickness of λ / 4, M is a medium-refractive-index material with an optical thickness of λ / 4, H is a high-refractive-index material with an optical thickness of λ / 4, n is the number of periods, and x, y, and z are the thickness coefficients of the low-refractive-index, medium-refractive-index, and high-refractive-index material films, respectively.

2. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1, characterized in that, The number of dielectric film cycles n is 1-10, and the film thickness coefficients x, y, z are between 0.1 and 3.

3. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1 or 2, characterized in that, The substrate material is Cu, Mo, Ge, Si, chalcogenide glass, ZnSe, or ZnS.

4. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1 or 2, characterized in that, The transition layer material is Cr or a chromium-nickel alloy.

5. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1 or 2, characterized in that, The metal layer material is Au, Ag, or Al.

6. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1 or 2, characterized in that, The high refractive index medium material is Ge or PbTe.

7. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1 or 2, characterized in that, The medium refractive index material is ZnSe or ZnS.

8. The long-wave infrared laser reflector with a three-dielectric structure according to claim 1 or 2, characterized in that, The low-refractive-index medium material is BaF2, YF3, or YbF3.

Images