A film structure and preparation method for considering stealth and laser protection

Abstract

The application belongs to the technical field of thin film materials, and particularly relates to a thin film structure and a preparation method, which give consideration to stealth and laser protection, comprising a multilayer thin film arranged on a substrate and a phase change reflection layer arranged on the multilayer thin film, wherein the multilayer thin film is composed of high-refractive-index material layers and low-refractive-index material layers arranged alternately, and the phase change reflection layer comprises a phase change film layer and a phase compensation medium layer arranged on the multilayer thin film in sequence, and the material of the phase compensation medium layer is Si, Ge, ZnS, ZnSe, SiO2, CaF2 or Al2O3. The application can simultaneously have the effects of good laser protection, laser stealth and infrared stealth, and has a good heat management effect.

Description

Technical Field

[0001] This invention belongs to the field of thin film materials technology, specifically relating to a thin film structure and preparation method that combines stealth and laser protection. Background Technology

[0002] Laser detection and laser destruction have long been potential technological fields for lasers. Both fields are closely related to infrared targets, leading to two application needs: infrared laser stealth and laser protection. To date, there is no feasible solution that is compatible with both infrared laser stealth and laser protection.

[0003] Research on Laser Protective Thin Films with Visible Light Stealth Function, Chen Hao, Master's Thesis, Xiamen University, 2021. To improve the laser damage resistance of laser protective thin films, traditional design methods mainly utilize the high reflectivity of metals to achieve protection: leveraging the characteristic of phase change materials such as V₂O₅ that transition from a semiconductor to a metallic state at high temperatures, high reflectivity can be achieved with fewer film layers. This paper describes an omnidirectional reflective thin film designed and fabricated using a one-dimensional photonic crystal, making it possible to simultaneously possess high reflectivity and almost omnidirectional reflectivity. Furthermore, the laser protective thin film exhibits different colors depending on the environment, thus achieving visible light stealth. However, it can only achieve visible light stealth and cannot achieve infrared or laser stealth.

[0004] Application publication number CN 116299822 A discloses a silicon-based photonic crystal capable of infrared / laser / visible light compatible stealth and its fabrication method. From bottom to top, the crystal consists of a substrate, an infrared band film, and a visible light band film. The infrared band film is composed of alternatingly sputtered thin films of different thicknesses of high and low refractive index materials. The outermost visible light band film consists of a single layer of low refractive index material. The total number of layers in this silicon-based photonic crystal is 12-16. The high refractive index materials in the infrared band film include Ge, Te, and Si, while the low refractive index materials include MgF2, CaF2, YbF3, SiO2, TiO2, ZnS, and ZnSe. The matching of the high and low refractive index materials must satisfy the condition nH / nS ≥ 1.92. The low refractive index materials in the outermost visible light band film include MgF2, CaF2, YbF3, SiO2, TiO2, ZnS, and ZnSe. It uses two film layers to achieve infrared / visible light compatible stealth.

[0005] To achieve both infrared laser stealth and laser protection compatibility, it is necessary to have stealth performance (high transmittance / high absorption) when detecting low-power lasers, while reducing absorption performance when damaged by high-power lasers to avoid damage to military targets. This requires the same material to have two completely different absorption properties at different powers, and these properties should not have any adverse effects on each other, which brings great difficulties to the design. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a thin film structure and preparation method that takes into account both stealth and laser protection, which can simultaneously have good laser protection, laser stealth and infrared stealth effects, and also has good thermal management effect.

[0007] This invention provides a thin film structure that combines stealth and laser protection, including a multilayer thin film disposed on a substrate and a phase change reflective layer disposed on the multilayer thin film. The multilayer thin film is composed of alternating high refractive index material layers and low refractive index material layers. The phase change reflective layer includes a phase change film layer and a phase compensation medium layer disposed sequentially on the multilayer thin film. The material of the phase compensation medium layer is Si, Ge, ZnS, ZnSe, SiO2, CaF2, or Al2O3.

[0008] As one embodiment, the substrate is a dielectric material or a flexible substrate.

[0009] As one embodiment, the substrate material is Si, SiO2, aerogel, PMMA, PET, or PI.

[0010] As one embodiment, it also includes a reflective separator disposed between the substrate and the multilayer thin film, the reflective separator being made of a metallic material.

[0011] In one embodiment, the material of the reflective interlayer is Ti, Cr, Ni, Ag, Au, or Al.

[0012] In one embodiment, the high refractive index material layer is made of Si, Ge, or Ge2Sb2Te5, the low refractive index material layer is made of YbF3, ZnS, ZnSe, SiO2, CaF2, or Al2O3, and the phase change film layer is made of Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1, or In3SbTe2.

[0013] In one embodiment, the substrate is made of SiO2, the high-refractive-index material is Si, the low-refractive-index material is SiO2, the phase change film is made of VO2 with a thickness of 200 nm, the phase compensation dielectric layer is made of Ge with a thickness of 80 nm, and the multilayer film, from top to bottom, is SiO2 / Si / SiO2 / Si / SiO2 / Si / SiO2 / Si with thicknesses of [missing information].

[0014] 279 / 360 / 973 / 101 / 956 / 987 / 729 / 953nm.

[0015] In one embodiment, the reflective interlayer is made of Ti or Cr. The substrate is made of SiO2, the high-refractive-index material is Si, the low-refractive-index material is YbF3, the phase change film is made of VO2 with a thickness of 200 nm, the phase compensation dielectric layer is made of Si with a thickness of 110 nm, and the multilayer film, from top to bottom, is YbF3 / YbF3 / Si / YbF3 / Si / YbF3 / Si / Si with thicknesses of 257 / 359 / 244 / 933 / 947 / 910 / 688 / 218 nm respectively.

[0016] This invention provides a method for preparing a thin film structure that combines stealth and laser protection. The method involves depositing a multilayer thin film on a substrate using a thermal evaporation method, then preparing a phase change film layer using a magnetron sputtering method, and finally depositing a phase compensation dielectric layer using a thermal evaporation method.

[0017] The beneficial effects of this invention are that it uses a genetic algorithm to design an infrared stealth multilayer thin film structure based on phase-deformable materials, achieving compatibility between infrared laser stealth and laser protection, which is of great significance for expanding the application of infrared stealth.

[0018] This invention proposes an intelligent infrared stealth coating and its design / manufacturing method, thereby achieving compatibility of laser protection, laser stealth, and infrared stealth. For a transparent multilayer film, the multilayer film is deposited on a quartz substrate. Under normal temperature conditions, this coating possesses capabilities such as infrared stealth, thermal management, and laser stealth. Specific performance indicators are as follows: low emissivity of the mid-infrared atmospheric window in both mid-wave and long-wave infrared bands, and low reflectivity (high absorption) of 1.06μm and 10.6μm dual-band lasers, thus achieving compatibility between infrared thermal stealth and laser stealth. As the incident laser power increases, the multilayer film characteristics transition from laser stealth to laser protection, and the proposed intelligent infrared stealth coating also intelligently shifts from laser reflection suppression to laser reflection enhancement, further solving the compatibility problem between infrared thermal stealth and infrared laser protection. For a non-transparent multilayer film with a metal reflective layer, under normal temperature conditions, this coating possesses capabilities such as infrared stealth and laser stealth. Furthermore, it can also achieve adaptive switching between laser stealth and laser protection, further solving the compatibility problem between infrared stealth and infrared laser protection.

[0019] The phase compensation layer is used to compensate for the reflection phase of the vanadium dioxide thin film during laser protection, thereby achieving high reflectivity for 1.06μm and 10.6μm lasers. Ge and Si are preferred as phase compensation layers because Ge and Si, as high refractive index materials, can meet the phase compensation requirements with thinner layers. If CaF2 or SiO2 is used as phase compensation, a thickness of 2-3 times is required. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the optimal film structure in Embodiment 1 of the present invention.

[0021] Figure 2 The final optimized structure of Embodiment 1 of the present invention is compatible with the infrared spectrum in infrared stealth mode.

[0022] Figure 3 The final optimized structure of Embodiment 1 of the present invention is compatible with the infrared spectrum under laser protection mode.

[0023] Figure 4 The final optimized structure of Embodiment 1 of the present invention is compatible with the electric field distribution inside the thin film at a wavelength of 1.06 μm in infrared stealth mode.

[0024] Figure 5 The final optimized structure of Embodiment 1 of the present invention is compatible with the electric field distribution inside the thin film at a wavelength of 10.6 μm in infrared stealth mode.

[0025] Figure 6 This illustrates the relationship between the number of iterations and population quality in Embodiment 1 of the present invention.

[0026] Figure 7 The infrared reflection spectrum of the overall structure with and without the phase change reflective layer C in Embodiment 1 of the present invention is shown.

[0027] Figure 8 This is a schematic diagram of the optimal film structure of Embodiment 2 of the intelligent infrared stealth multilayer film of the present invention.

[0028] Figure 9 The final optimized structure of Embodiment 2 of the present invention is compatible with the infrared spectrum in infrared stealth mode.

[0029] Figure 10 The final optimized structure of Embodiment 2 of the present invention is compatible with the infrared spectrum under laser protection mode.

[0030] Figure 11 The final optimized structure of Embodiment 2 of the present invention is compatible with the electric field distribution inside the thin film at a wavelength of 1.06 μm in infrared stealth mode.

[0031] Figure 12 The final optimized structure of Embodiment 2 of the present invention is compatible with the electric field distribution inside the thin film at a wavelength of 10.6 μm in infrared stealth mode.

[0032] Figure 13 This illustrates the relationship between the number of iterations and population quality in Embodiment 2 of the present invention.

[0033] Figure 14 The infrared reflection spectrum of the overall structure with and without the phase change reflective layer C in Embodiment 2 of the present invention.

[0034] Figure 15 This is a schematic diagram of the structure of Embodiment 3 of the present invention.

[0035] Figure 16 The infrared reflectance spectra of Embodiment 3 of the present invention are obtained under two different modes. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] In the initial structure, we designed a transparent multilayer thin film structure on substrate A, which consists of two parts. The upper part is a phase-change reflective layer C used to generate dual-band laser reflection at high energy levels for laser protection compatibility, while the lower part consists of multiple high- and low-refractive-index thin films as a smart algorithm optimization layer B (i.e., multilayer thin films) for compatibility with infrared thermal stealth, laser stealth, and thermal management at room temperature. Based on a genetic algorithm (GA), we optimized the materials and thicknesses of the eight thin films, which consist of two infrared high- and low-refractive-index materials with thicknesses ranging from 0 to 1000 nanometers.

[0039] A thin-film structure that combines stealth and laser protection includes a substrate A, which can be a dielectric material or a flexible substrate, such as Si, SiO2, aerogel, PMMA, PET, PI, etc. An intelligent algorithm optimization layer B is provided on top, consisting of eight layers of infrared high / low refractive index media with thicknesses ranging from 0 to 1000 nm. Suitable high refractive index media include Si, Ge, Ge2Sb2Te5, etc., and suitable low refractive index media include ZnS, ZnSe, SiO2, CaF2, YbF3, Al2O3, etc. A phase-change reflective layer C is also included, consisting of a phase compensation medium layer and a phase-change film layer. The phase compensation medium layer can be made of Si, Ge, ZnS, ZnSe, SiO2, CaF2, Al2O3, etc., and the phase-change film layer can be made of Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1, In3SbTe2, etc.

[0040] In this embodiment 1, the thin film composition and thickness of the algorithm optimization layer B are optimized by a genetic algorithm to achieve ideal infrared stealth performance, specifically including: 1.06μm / 10.6μm dual-wavelength infrared laser stealth, 3-5μm / 8-14μm dual-band mid-infrared atmospheric window thermal stealth, and 5-8μm non-infrared atmospheric window band radiative thermal management.

[0041] Specifically, in this embodiment 1, the substrate A is made of SiO2 with a thickness greater than 0.3 mm; the intelligent algorithm optimization layer B consists of 8 layers of infrared high / low refractive index medium Si / SiO2 with a thickness in the range of 0 to 1000 nm; the top phase change reflective layer C consists of two thin film structures of Ge and VO2 with thicknesses of 80 nm and 200 nm, respectively.

[0042] The thickness and material of the optimized layer in this invention are designed using an intelligent genetic algorithm, which includes the following steps:

[0043] Step 1: Determine the function of the device. Define the quality factor function representing the device's function:

[0044] FOM=a×(1-R1)+b×R2+c×(1-R3)+d×R4+e×(1-R5)

[0045] In the formula, R1, R2, R3, R4, and R5 each correspond to a performance index, including reflectivity at 1.06 μm; average reflectivity in the 3-5 μm wavelength range; average reflectivity in the 5-8 μm wavelength range; average reflectivity in the 8-14 μm wavelength range; and reflectivity at 10.6 μm. Here, a, b, c, d, and e represent weighting factors corresponding to different performance indices, which can be used to emphasize infrared stealth, laser stealth, and thermal management performance, respectively. In this embodiment, a, b, c, d, and e are all set to 0.2 in order to obtain a smart infrared stealth structure with higher compatibility.

[0046] Step 2: Set the optimization range and features of the optimization layer. For the 8 layers of material in the intelligent algorithm optimization layer B, the material composition can be selected as Si or SiO2. The thickness of each layer can be any integer value within the range of 0–1000 nm.

[0047] Step 3: Genetic Algorithm Optimization. The initial population consists of 2000 individuals, each represented by 16 parameters (eight bits representing the material parameters of each of the eight-layer structure, and the other eight bits representing the thickness parameters of each of the eight layers). The 2000 individuals are sorted, and the optimal individual with the highest FOM (Form of Mean Occurrence) ranking becomes the parent, with 1000 parent individuals. Except for the optimal individual, which is retained in the next generation, the remaining offspring are generated through crossover and mutation processes. The crossover process involves randomly selecting a crossover point between the binary codes of two parents and replacing and recombining them to form new individuals. One iteration is the process of performing a single FOM calculation on all 2000 individuals to derive the next generation's parents. The entire algorithm iterates 35 times, terminating when an individual in the offspring has a FOM greater than 99%. The mutation probability (Mutation_rate) is set to 0.3. The mutation process involves the random mutation point of the binary code of the new individuals generated by the crossover process changing (i.e., a code of 0 mutates to 1, and a code of 1 mutates to 0).

[0048] Step 4: Obtain the final structure. After 35 iterations, the parameter features of the final sample structure are as follows: Figure 1 As shown, this includes the components and thickness of each layer of the structure.

[0049] Specifically, the material composition and thickness (from top to bottom) of each layer of the final sample structure are as follows:

[0050] SiO2 / Si / SiO2 / Si / SiO2 / Si / SiO2 / Si;

[0051] 279 / 360 / 973 / 101 / 956 / 987 / 729 / 953nm.

[0052] Figure 2The infrared spectrum obtained through numerical calculation includes reflectance R, transmittance T, and absorptivity A. The solid black line represents infrared reflectance R, the solid gray line represents transmittance T, and the dashed gray line represents absorptivity A. Absorptivity A is given by the formula A(λ) = 1 - R(λ) - T(λ), where λ represents wavelength. The conversion efficiency between laser stealth and laser protection is determined by the difference in reflectance before and after the phase transition at a specified wavelength, as shown in the following expression:

[0053]

[0054]

[0055] Wherein, Trans represents the conversion efficiency of laser stealth to laser protection, R represents spectral reflectivity, the superscript high indicates high power operation, the superscript low indicates low power operation, and the subscript indicates the corresponding operating wavelength.

[0056] Combination Figure 2 and Figure 3 The performance indicators are as follows: as shown by the gray line in the figure, R 1.06μm =18.1%; R 10.6μm =1.2%; R 3-5μm =90.5%, R 5-8μm =76.4%; R 8-14μm =45.4%. At high temperatures, as shown by the black line in the figure, the laser protection performance shows reflection efficiencies of 0.74 and 0.73 for the 1.06μm and 10.6μm dual-band lasers, respectively. Laser stealth-laser protection conversion efficiency Trans 1.06μm =55.9%, Trans 10.6μm =71.8%.

[0057] Step 5: Processing and Preparation. First, a Si / SiO2 multilayer thin film structure is physically deposited using thermal evaporation. If two adjacent film layers have the same material composition, they can be merged into a single thin film structure for deposition. The vacuum level is 10. -3 The deposition rate was 1 nm / s at Pa. The upper VO2 thin film was then prepared using magnetron sputtering, with a vacuum level of 10 Pa during the preparation process. -1 The deposition rate was 0.2 nm / s. After deposition, the film was annealed for 1 hour at a pressure of 1 Pa and a temperature of 450 °C. Then, a Ge thin film was deposited on the top layer using thermal evaporation as described above. Finally, a transparent intelligent infrared stealth multilayer film sample optimized by the above-mentioned intelligent algorithm was obtained.

[0058] exist Figure 4 Further analysis was conducted on the electric field distribution inside the thin film at a wavelength of 1.06 μm at room temperature (low laser energy threshold), revealing that electric field loss mainly occurs in the Ge film layer.

[0059] exist Figure 5 Further analysis was conducted on the electric field distribution inside the thin film at a wavelength of 10.6 μm at room temperature (low laser energy threshold). It was found that the electric field loss mainly occurred in the SiO2 substrate layer, and the intelligent algorithm optimization layer and phase change layer mainly played the role of anti-reflection to enhance the electric field distribution reaching the SiO2 substrate layer.

[0060] like Figure 6 The figure shows the changes in the population mean and the optimal population value over 50 iterations. It can be seen that the population mean continuously increases throughout the process, indicating that the population quality is constantly improving and evolving in the direction required by the FOM (Form of Mean). Specifically, it increases from 0.5 to above 0.65. The optimal population value converges in the 41st generation and remains there until the genetic algorithm completes its iterations. The optimal sample FOM is 0.743.

[0061] Figure 7 Comparing the infrared reflectance spectra of the overall structure with and without the phase-change reflective layer C reveals a strict matching mechanism for the multilayer film structure designed in this invention. After removing the phase-change reflective layer C, multiple resonance peaks at 1.06 μm and 10.6 μm shift. Furthermore, most resonance peaks are distorted, such as interference peaks in the 3-5 μm and 5-8 μm wavelength ranges. At low energy thresholds, the phase-change reflective layer C, substrate layer A, and intelligent algorithm optimization layer B exhibit phase matching, resulting in high-performance infrared stealth-compatible thermal management. At high energy thresholds, the phase-change reflective layer C acts as an intelligent conversion layer, enabling the multilayer film to transition from infrared stealth-compatible thermal management to laser protection functionality. Therefore, the structure described in this invention is unified, and each film layer cannot function independently.

[0062] Example 2

[0063] In the initial structure, we designed a non-transparent multilayer thin film structure on substrate A. The upper part of the substrate consists of three multilayer thin films: a reflective barrier layer B, closely attached to the substrate, to block (reflect) all infrared light from propagating downwards; a phase-change reflective layer D at the top, used to generate dual-band laser reflection at high energy levels for laser protection compatibility; and a middle part between the top and bottom, consisting of a multilayer high- and low-refractive-index thin film structure as a smart algorithm optimization layer C, compatible with infrared thermal stealth and laser stealth at room temperature. Based on a genetic algorithm (GA), we optimized the materials and thicknesses of the eight thin films, using two types of infrared high- and low-refractive-index materials with thicknesses ranging from 0 to 1000 nanometers.

[0064] A smart infrared stealth multilayer thin film structure includes a substrate A, which can be a dielectric material or a flexible substrate, such as Si, SiO2, aerogel, PMMA, PET, PI, etc.; a reflective separator B is provided on the upper part, which can be a metallic material such as Ti, Cr, Ni, Ag, Au, Al, etc.; and a smart algorithm optimization layer C, which consists of 8 layers of infrared high and low refractive index media with a thickness in the range of 0 to 1000 nm. The high refractive index media can include Si, Ge, Ge2Sb2Te5, etc., and the low refractive index media can include ZnS, ZnSe, SiO2, CaF2, YbF3, Al2O3, etc. The phase change reflective layer D consists of two thin film structures: a phase compensation medium and a phase change film. The phase compensation medium can be made of materials such as Si, Ge, ZnS, ZnSe, SiO2, CaF2, Al2O3, etc., while the phase change film can be made of materials such as Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1, In3SbTe2, etc.

[0065] In this embodiment 2, the thin film composition and thickness of the algorithm optimization layer C are optimized by a genetic algorithm to achieve ideal infrared stealth performance, specifically including: infrared laser stealth with dual wavelengths of 1.06μm and 10.6μm, and mid-infrared atmospheric window thermal stealth with dual bands of 3-5μm and 8-14μm.

[0066] Specifically, in this embodiment 2, the substrate A is made of SiO2 with a thickness greater than 0.3 mm; the reflective interlayer B is made of metallic Ti with a thickness of 100 nm; the intelligent algorithm optimization layer C consists of eight layers of infrared high / low refractive index dielectric Si / SiO2 with thicknesses ranging from 0 to 1000 nm. The top phase change reflective layer D consists of two thin film structures, Ge and VO2, with thicknesses of 80 nm and 200 nm, respectively.

[0067] The thickness and material of the optimized layer in this invention are designed using an intelligent genetic algorithm, which includes the following steps:

[0068] Step 1: Determine the function of the device. Define the quality factor function representing the device's function:

[0069] FOM=a×(1-R1)+b×R2+c×(1-R3)+d×R4

[0070] In the formula, R1, R2, R3, and R4 each correspond to a performance index, including reflectivity at 1.06 μm; average reflectivity in the wavelength range of 3-5 μm; reflectivity at 10.6 μm; and average reflectivity in the wavelength range of 8-14 μm. a, b, c, and d represent weighting factors corresponding to different performance indices, which can be used to improve the emphasis on infrared stealth, laser stealth, and thermal management performance, respectively. In this embodiment, a, b, c, and d are all set to 0.25 in order to obtain a smart infrared stealth structure with higher compatibility.

[0071] Step 2: Set the optimization range and features for the optimization layer. For the 8 layers of material in the intelligent algorithm optimization layer C, the material composition can be selected as Ge or ZnS. The thickness of each layer can be any integer value within the range of 0–1000 nm.

[0072] Step 3: Genetic Algorithm Optimization. The initial population consists of 2000 individuals, each represented by 16 parameters (eight bits representing the material parameters of each of the eight-layer structure, and the other eight bits representing the thickness parameters of each of the eight layers). The 2000 individuals are sorted, and the best individual with the highest FOM (Form of Mean Occurrence) ranking becomes the parent, with 1000 parent individuals. Except for the best individual, which is retained in the next generation, the remaining offspring are generated through crossover and mutation processes. The crossover process involves randomly selecting a crossover point between the binary codes of two parents and replacing and recombining them to form a new individual. One iteration is the process of performing a single FOM calculation on all 2000 individuals to derive the next generation's parents. The entire algorithm iterates 40 times, terminating when there are offspring individuals with a FOM greater than 99%. The mutation probability is set to 0.3. The mutation process involves the random mutation point of the binary code of the new individuals generated by the crossover process changing (i.e., a code of 0 mutates to 1, and a code of 1 mutates to 0).

[0073] Step 4: Obtain the final structure. After 40 iterations, the parameter features of the final sample structure are as follows: Figure 8 As shown, this includes the components and thickness of each layer of the structure.

[0074] Specifically, the material composition and thickness of each layer of the final sample structure are as follows:

[0075] Si / SiO2 / Si / SiO2 / SiO2 / Si / Si / SiO2;

[0076] 177 / 153 / 242 / 562 / 611 / 30 / 210 / 479nm.

[0077] Figure 9The infrared spectrum obtained through numerical calculation includes reflectance R, transmittance T, and absorptivity A. The solid black line represents infrared reflectance R, the solid gray line represents transmittance T, and the dashed gray line represents absorptivity A. Absorptivity A is given by the formula A(λ) = 1 - R(λ) - T(λ), where λ represents wavelength. The conversion efficiency between laser stealth and laser protection is determined by the difference in reflectance before and after the phase transition at a specified wavelength, as shown in the following expression:

[0078]

[0079]

[0080] Wherein, Trans represents the conversion efficiency of laser stealth to laser protection, R represents spectral reflectivity, the superscript high indicates high power operation, the superscript low indicates low power operation, and the subscript indicates the corresponding operating wavelength.

[0081] Combination Figure 9 and Figure 10 The performance indicators are as follows: as shown by the gray line in the figure, R 1.06μm =17.3%; R 10.6μm =5.2%; R 3-5μm =88.2%, R 8-14μm =67.4%. At high temperatures, as shown by the black line in the figure, the laser protection performance shows reflection efficiencies of 0.74 and 0.73 for the 1.06μm and 10.6μm dual-band lasers, respectively. Laser stealth-laser protection conversion efficiency Trans 1.06μm =56.7%, Trans 10.6μm =67.8%.

[0082] Step 5: Fabrication. First, a Ti / Si / SiO2 multilayer thin film structure is physically deposited using thermal evaporation to fabricate the two functional layers: the reflective interlayer B and the intelligent algorithm optimization layer C. If two adjacent film layers have the same material composition, they can be merged into a single thin film structure for deposition. The vacuum level is less than 10. -3 The deposition rate was 1 nm / s at Pa. The upper VO2 thin film was then prepared using magnetron sputtering, with a vacuum level greater than 10 Pa during the preparation process. -1 The deposition rate was 0.2 nm / s. After deposition, the film was annealed for 1 hour at a pressure of 1 Pa and a temperature of 450 °C. Then, a Ge film was deposited on the top layer using thermal evaporation as described above. Finally, a non-transparent intelligent infrared stealth film sample optimized by the aforementioned intelligent algorithm was obtained.

[0083] exist Figure 11Further analysis was conducted on the electric field distribution inside the thin film at a wavelength of 1.06 μm at room temperature (low laser energy threshold), revealing that electric field loss mainly occurs in the Ge film layer.

[0084] exist Figure 12 Further analysis was conducted on the electric field distribution inside the thin film at a wavelength of 10.6 μm at room temperature (low laser energy threshold). It was found that the electric field loss mainly occurred in the metal separator, and the intelligent algorithm optimization layer and phase change layer mainly played the role of anti-reflection to enhance the electric field distribution reaching the titanium metal reflective separator.

[0085] like Figure 13 The figure shows the changes in the population mean and the optimal population value over 50 iterations. It can be seen that the population mean continuously increases throughout the process, indicating that the population quality is constantly improving and evolving towards the set FOM (Frame of Mean). Specifically, it increases from 0.54 to over 0.66. The optimal population value converges in the 22nd generation and remains there until the genetic algorithm completes its iterations. The optimal sample FOM is 0.779.

[0086] Figure 14 The infrared reflectance spectra of the overall structure with and without the phase change reflective layer D were compared, showing that the non-transparent multilayer film structure designed in the invention also has a strict matching mechanism. After removing the phase change reflective layer D, multiple resonance peaks at 1.06 μm and 10.6 μm, among others, drifted. Furthermore, most resonance peaks were distorted, such as interference peaks in the 3-5 μm and 5-8 μm wavelength ranges. These drifts or distortions will lead to a decrease or failure of the multilayer optical film's function. Therefore, the metal reflective layer B, the intelligent algorithm optimization layer C, and the phase change reflective layer D in the thin film are a unified whole and work together to achieve their functions. At low energy thresholds, the phase change reflective layer D, the metal reflective layer B, and the intelligent algorithm optimization layer C have a phase matching effect, thus bringing high-performance compatibility between infrared thermal stealth and laser stealth. At high energy thresholds, the phase reflective layer C acts as an intelligent conversion layer, enabling the multilayer film to transform from compatibility with infrared thermal stealth and laser stealth to laser protection functionality. Therefore, the structure described in the invention is unified, and each film layer cannot function independently. Of course, it should be noted that due to the presence of the metal reflective layer B, the incident electromagnetic waves are blocked in this layer, therefore the substrate material does not interact with the structure. The aforementioned opaque smart infrared multilayer film system is a substrate-insensitive structure; when other substrate materials are replaced, the structure can still perfectly match existing functions.

[0087] Example 3

[0088] Structure as Figure 15 As shown, its substrate is a quartz substrate with a thickness greater than 0.3 mm. The composition and thickness of each of the remaining layers are as follows:

[0089] Si / VO2 / YbF3 / YbF3 / Si / YbF3 / Si / YbF3 / Si / Si / Cr;

[0090] 110 / 200 / 257 / 359 / 244 / 933 / 947 / 910 / 688 / 218 / 200nm.

[0091] The substrate is made of SiO2, the reflective separator B is made of Cr, the high refractive index material is Si, the low refractive index material is YbF3, the phase change film is made of VO2 and has a thickness of 200 nm; the phase compensation dielectric layer is made of Si and has a thickness of 110 nm.

[0092] In our preferred selection, we chose Si as both the high-refractive-index material layer and the phase-compensation dielectric layer because Si has a wider photonic bandgap compared to high-refractive-index materials such as Ge, thus ensuring relatively higher optical transparency (extremely low extinction coefficient) in the 1-14 μm infrared wavelength range. We chose YbF3 as the low-refractive-index material because, compared to SiO2, it does not exhibit phonon polarization near the 10 μm wavelength, thereby ensuring low loss over a wide infrared wavelength range. Furthermore, YbF3 has a lower refractive index (1.48–1.52) and a wider transparency bandwidth (0.6–12 μm) compared to other infrared low-refractive-index materials.

[0093] like Figure 16 The image shows the reflectance spectra from near-infrared to mid-infrared (1–14 μm). Under ambient temperature and low-energy threshold detection laser irradiation, R… 1.06μm =8%; R 10.6μm =2%; R 3-5μm =91%, R 8-14μm =81%. At high temperatures, the spectral characteristics of dual-band lasers shift from high absorption to high reflection, thus achieving the purpose of laser protection. The reflection efficiencies of 1.06μm and 10.6μm dual-band lasers are 77% and 72%, respectively. Laser stealth-laser protection conversion efficiency Trans 1.06μm =69%, Trans 10.6μm =70%.

[0094] In low-power mode, the overall device performance (FOM) reaches 90%, significantly higher than the Si / SiO2 high / low refractive index film combination in Example 2 (83%). Furthermore, the selection of YbF3 as the low refractive index material, compared to Example 2 (R... 8-14μm =67.4%) Long-wave infrared stealth performance has been significantly improved (R 8-14μm =81%), making the device more practical in the field of infrared stealth.

[0095] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0096] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A thin-film structure that combines stealth and laser protection, characterized in that, The invention includes a multilayer thin film disposed on a substrate and a phase change reflective layer disposed on the multilayer thin film. The multilayer thin film is composed of alternating layers of high refractive index material and low refractive index material. The phase change reflective layer includes a phase change film layer and a phase compensation dielectric layer disposed sequentially on the multilayer thin film. The material of the phase compensation dielectric layer is Si or Ge. The high refractive index material layer is made of Si, Ge, or Ge2Sb2Te5, and the low refractive index material layer is made of ZnS, ZnSe, SiO2, CaF2, YbF3, or Al2O3; the phase change film layer is made of Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1, or In3SbTe2.

2. The thin-film structure that combines stealth and laser protection as described in claim 1, characterized in that, The substrate is a dielectric material or a flexible substrate.

3. The thin-film structure that combines stealth and laser protection as described in claim 2, characterized in that, The substrate material is Si, SiO2, aerogel, PMMA, PET, or PI.

4. The thin-film structure that combines stealth and laser protection as described in claim 1 or 2, characterized in that, It also includes a reflective separator disposed between the substrate and the multilayer thin film, wherein the reflective separator is made of a metallic material.

5. The thin-film structure that combines stealth and laser protection as described in claim 4, characterized in that, The material of the reflective interlayer is Ti, Cr, Ni, Ag, Au or Al.

6. The thin-film structure combining stealth and laser protection as described in any one of claims 1-3, characterized in that, The substrate is made of SiO2, the high-refractive-index material is Si, the low-refractive-index material is SiO2, the phase change film is made of VO2 and has a thickness of 200 nm; the phase compensation dielectric layer is made of Ge and has a thickness of 80 nm; in the multilayer film, from top to bottom, the layers are SiO2 / Si / SiO2 / Si / SiO2 / Si / SiO2 / Si and the thicknesses are 279 / 360 / 973 / 101 / 956 / 987 / 729 / 953 nm respectively.

7. The thin-film structure that combines stealth and laser protection as described in claim 5, characterized in that, The material of the reflective layer is Ti or Cr.

8. The thin-film structure that combines stealth and laser protection as described in claim 7, characterized in that, The substrate is made of SiO2, the high refractive index material is Si, the low refractive index material is YbF3, the phase change film is made of VO2 and has a thickness of 200 nm; the phase compensation dielectric layer is made of Si and has a thickness of 110 nm; in the multilayer film, from top to bottom, the layers are YbF3 / YbF3 / Si / YbF3 / Si / YbF3 / Si / Si and the thicknesses are 257 / 359 / 244 / 933 / 947 / 910 / 688 / 218 nm respectively.

9. A method for preparing a thin film structure that combines stealth and laser protection as described in any one of claims 1-8, characterized in that, Multilayer thin films were deposited on the substrate using thermal evaporation, followed by the preparation of a phase change film layer using magnetron sputtering, and finally the deposition of a phase compensation dielectric layer using thermal evaporation.

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