A laser thin film structure and its preparation method

Abstract

This invention discloses a laser thin film structure and its fabrication method. The thin film structure comprises a first dielectric layer / metal layer / second dielectric layer / substrate layer, wherein the second dielectric layer is formed by alternating deposition of a low-refractive-index dielectric material and a high-refractive-index dielectric material; the structural expression of the second dielectric layer is H(LH)^s, where H represents a high-refractive-index dielectric material with an optical thickness of λ / 4, L represents a low-refractive-index dielectric material with an optical thickness of λ / 4, and s represents the number of film periods. This invention can improve camouflage capabilities while ensuring excellent laser protection performance.

Description

Technical Field

[0001] This invention relates to the field of laser thin film technology, and more particularly to an improved DMD thin film. Background Technology

[0002] With the rapid development of various detection technologies, single-band stealth materials are no longer sufficient to meet the demands of evading detection, identification, and attack. Multi-spectrum compatible stealth materials have become an inevitable trend. Camouflage technology is crucial for protecting military equipment and is widely used in various military vehicles (aircraft, ships, tanks, artillery, and armored vehicles, etc.). The design of multi-spectrum compatible stealth materials often faces technical bottlenecks due to conflicting stealth principles across different frequency bands. For example, the requirements for low infrared emission and high visible light transmittance spectral response are mutually restrictive and contradictory. Current detection technologies tend towards multi-source, multi-mode integration, making multi-band compatible camouflage particularly important.

[0003] To meet the requirements of multi-band compatible camouflage, various camouflage technologies have been proposed, such as Fabry-Perot (FP) cavities, photonic crystals, metasurfaces, and multilayer optical coatings. Patent CN106383376A proposes a multilayer thin-film infrared stealth material based on YbF3 and ZnSe, achieving low emissivity in the infrared band for effective infrared stealth while simultaneously maintaining radar stealth capabilities. Patent CN112346162B proposes a metal-dielectric type spectrally selective multi-band stealth film that achieves mid-infrared and 1.064µm laser wavelength compatibility through alternating Si and W layers. These technologies effectively control the absorption or reflection of specific wavelengths of electromagnetic waves by introducing nanostructures. However, most multi-band compatible camouflage films focus on the long-wavelength band, and due to the presence of lossy materials and resonant absorption cavities, their appearance is often opaque or dark.

[0004] To reduce the intensity of the detection signal from equipment, issues such as infrared emissivity, microwave reflection loss, and laser absorption need to be addressed. Currently, research on optical window camouflage with high transmittance in the visible light band and low emissivity in the infrared band is insufficient. The essence of this camouflage is to improve impedance matching in the visible light band, thereby guiding more light into the thin film rather than reflecting it back, and ensuring that the film blocks infrared radiation at the atmospheric window. Improving the camouflage performance of optical windows requires achieving high transmittance in the 380-780 nm wavelength range and suppressing infrared signals to reduce the radiation temperature of the target surface. Furthermore, these characteristics hold promise for combination with visible light camouflage coatings or equipment to extend their infrared camouflage capabilities. However, as infrared camouflage performance improves, a decrease in visible light transparency is inevitable.

[0005] The dielectric / metal / dielectric structure resembles a sandwich, where high transmittance is achieved using two dielectric layers through optical interference and near-perfect impedance matching with free space. Furthermore, the integrated metal layer is crucial for providing enhanced conductivity, thereby suppressing infrared thermal emission. While a thicker metal layer may result in low infrared emissivity, it can also reduce visible light transmittance due to its reflective properties. Conversely, an ultrathin metal layer can lead to increased infrared emissivity due to high plasma resonance absorption, which may also result in decreased conductivity. Current dielectric / metal / dielectric structures are largely limited to transparent conductive films used in optoelectronic devices. By embedding a highly reflective metal layer between two dielectric layers, the structure can suppress visible light reflection from the metal layer, achieving a selective transmission enhancement effect.

[0006] Furthermore, in the complex and ever-changing battlefield environment of modern times, equipment faces threats from various detection and attack methods, including visual, infrared, and laser technologies. If equipment only possesses stealth capabilities but lacks effective protection, it becomes highly vulnerable to destructive attacks once detected, significantly reducing its survivability. Technologies that combine stealth and protection enable equipment to withstand various weapon attacks even when detected, thereby significantly improving its overall survivability. Traditional laser protection materials typically employ metals, ceramics, or polymer composites, relying primarily on strong absorption and scattering to suppress incident laser light and protect underlying equipment from damage. Patent CN108803182A proposes a laser protection film that, based on the properties of liquid crystal polymer materials, offers excellent laser protection, a wide protection angle, and good flexibility. Patent CN207164389U discloses a laser goggle that uses a multi-layered film structure to block harmful blue and infrared light while absorbing ultraviolet light that reflects light, thus protecting the eyes. However, while this energy absorption-based protection mechanism is effective in preventing laser damage to targets, it also faces the problem that its optical properties are difficult to meet stealth requirements.

[0007] Therefore, in order to counter the threats posed by monitoring equipment and laser weapons, it is urgent to develop efficient multi-band compatible stealth and laser protection methods. Summary of the Invention

[0008] In view of this, the purpose of this invention is to propose a laser thin film structure and its preparation method, which can improve camouflage capabilities while ensuring excellent laser protection performance.

[0009] According to one aspect of the present invention, a laser thin film structure is provided, the thin film structure being a first dielectric layer / metal layer / second dielectric layer / substrate layer, wherein the second dielectric layer is formed by alternating deposition of a low-refractive-index dielectric material and a high-refractive-index dielectric material; the structure expression of the second dielectric layer is H(LH)^s, where H represents a high-refractive-index dielectric material with an optical thickness of λ / 4, L represents a low-refractive-index dielectric material with an optical thickness of λ / 4, and s represents the number of film system periods.

[0010] In the above technical solution, based on the multiple optical effect coupling mechanism of the D'MD structure, the thin film has high visible light transparency, low infrared emissivity, and excellent laser protection capabilities. It can be attached to the camouflage coating surface of special vehicles to achieve infrared and visible light stealth and protection compatibility, and can also be used in cockpit windows to ensure heat insulation and temperature control while achieving infrared stealth effects without affecting visibility.

[0011] In some embodiments, the refractive index of the high-refractive-index medium material is 1.6-4.0;

[0012] The low-refractive-index medium material has a refractive index of 1.0-1.6.

[0013] In the above technical solution, in the dielectric material of the D'MD thin film structure, materials with a refractive index n of 1.6-4.0 can be used as high refractive index materials H (such as titanium dioxide (Tio2), tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), niobium pentoxide (Nb2O5), zirconium dioxide (ZrO2), yttrium trioxide (Y2O3), hafnium dioxide (HfO2), etc.), while materials with a refractive index n of 1.0-1.6 can be used as low refractive index materials L (such as silicon dioxide (SiO2), magnesium fluoride (MgF2), etc.). The reflection bandwidth increases with the increase of the refractive index ratio nH / nL. That is to say, the larger the refractive index ratio, the higher the reflectivity and the wider the reflection bandwidth.

[0014] In some embodiments, the material of the metal layer includes one or more of silver, gold, aluminum, and copper.

[0015] In the above technical solution, the intermediate metal layer plays a crucial role in visible light transmission and infrared reflection, and can be selected from materials such as silver (Ag), gold (Au), aluminum (Al), and copper (Cu).

[0016] According to another aspect of the present invention, a laser thin film structure is provided, the thin film structure being a first dielectric layer / a first metal layer / a second dielectric layer / a second metal layer / a third dielectric layer, wherein the second dielectric layer is formed by alternating deposition of a low-refractive-index dielectric material and a high-refractive-index dielectric material; the structure expression of the second dielectric layer is H(LH)^s, where H represents a high-refractive-index dielectric material with an optical thickness of λ / 4, L represents a low-refractive-index dielectric material with an optical thickness of λ / 4, and S represents the number of film system periods.

[0017] According to another aspect of the present invention, a method for preparing a laser thin film structure is provided, the method being used to prepare the aforementioned thin film structure;

[0018] High refractive index material, low refractive index material, and metal layer material are selected; the number of film system cycles is determined based on the number of cycles in which the reflectivity of the thin film to the center wavelength within the reflection band is greater than or equal to 99% and the difficulty of thin film preparation; the thin film is prepared by deposition based on the parameters determined above.

[0019] In the above technical solution, under normal incidence, the average reflectivity in the 1000-1100nm range reaches over 99%, and the 50% reflectivity bandwidth is over 250nm, which can achieve laser protection. Therefore, when selecting the number of cycles, it is necessary to consider that the reflectivity at the center wavelength remains above 99%, and determine the selectable number of cycles based on this premise. The final number of cycles is then determined by considering the fabrication difficulty. Thin films can be fabricated using physical vapor deposition (PVD) methods, including combinations of different techniques such as ion beam sputtering deposition (IBS), magnetron sputtering deposition (MS), electron beam evaporation (EB), or electron beam evaporation ion-assisted deposition (EBD-IAD). Alternatively, chemical vapor deposition (CVD) or liquid-phase coating methods for pearlescent thin films can also be used to prepare the films. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Schematic diagrams of the D'MD membrane structure (left) and the DMDMD' membrane structure (right);

[0022] Figure 2 The standing wave electric field distribution of a 33-layer TiO2 / SiO2 high reflectivity film (HL)^16H is shown.

[0023] Figure 3A comparison of the reflectance spectra before and after the outer layer of the D'MD film peels off;

[0024] Figure 4 A comparison of the visible light transmission spectra of the D'MD structure and monolayer metal;

[0025] Figure 5 A comparison of the initial design spectrum of the thin film and the spectrum when the error threshold is 5%;

[0026] Figure 6 A comparison of the reflectance spectra of the D'MD structure and conventional dielectric / metal / dielectric structures;

[0027] Figure 7 The infrared absorption spectrum of a visible-infrared stealth and laser protection compatible thin film structure is shown in one embodiment.

[0028] Figure 8 A comparison of the reflectance spectra of a visible-infrared stealth and laser protection compatible thin film structure as an example, showing the periodic variation.

[0029] Figure 9 This is the representation of the film color in the CIE 1931 chromaticity diagram as the thickness of the top dielectric varies (20-200 nm) according to Example 5. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] This invention provides a laser thin film structure and its preparation method, which can improve camouflage capabilities while ensuring excellent laser protection performance. The specific mechanism is as follows:

[0032] The D'MD structure is a composite optical thin film. The laser protection component requires high reflectivity and excellent resistance to laser damage. The basic structure of the high-reflectivity film is H(LH)^s (where H is a high-refractive-index material, L is a low-refractive-index material, and s is the film period), and its reflectivity for the center wavelength within the reflection band is generally no less than 99%. The stealth component utilizes the Stefan-Boltzmann law and Kirchhoff's laws. An infrared high-reflectivity layer reduces surface emissivity, effectively suppressing the target's thermal radiation and minimizing the radiation difference between the target and the environment. This makes the target difficult or impossible to detect by infrared detectors. In the visible light band, visible light stealth can be achieved by increasing transmittance, combined with camouflage coatings and electrochromic coatings.

[0033] Metals possess mirror-like properties, effectively blocking the propagation of electromagnetic waves and making them ideal materials for suppressing infrared signals. However, the high extinction coefficients of most metals, coupled with their high reflectivity in the optical band, make them unsuitable for achieving the desired transparent appearance. Metal thin films such as Au, Ag, and Cu exhibit strong effects in suppressing infrared radiation, but their light transmittance and thermal stability are poor. By stacking semiconductor dielectric layers with high optical transmittance and good thermal stability on both sides of the metal film, with the inner layer using a high refractive index n... H and low refractive index n L A periodic multilayer film composed of alternating stacks of two materials, with dielectric layers on both sides suppressing visible light reflection from the metal layer, achieves a selective transmission enhancement effect. The dielectric layers play a crucial role in altering impedance to induce more light transmission onto the film, requiring them to possess high transparency and a suitable refractive index. This forms... Figure 1 The diagram shows an alternating stacked dielectric / metal / dielectric (D'MD) structure (Material A is a high-refractive-index material, Material B is a low-refractive-index material, and Material C is a metal) and a symmetrical (D'MDMD') structure. The D'MD structure possesses the high visible light transmittance and low infrared emissivity characteristics of the traditional dielectric / metal / dielectric structure while also offering excellent laser protection. By designing the film material system, we can obtain optimal optical performance and achieve synergistic gains in optical effects such as visible light transmission induction, infrared radiation suppression, and high laser reflectivity.

[0034] Based on thin-film optics theory, the influence mechanism of D'MD structural characteristics on visible light transmission and infrared reflection spectra is analyzed using the transmission matrix theory calculation method. If a light wave with wavelength λ enters the composite thin-film structure from an air layer with refractive index n0 at an incident angle θ0, the light wave propagating in the thin-film dielectric layer can be regarded as the superposition of a down-going wave and an up-going wave. If d l n l θ l When the thickness, refractive index, and refraction angle of the l-th medium are respectively, the characteristic matrix M of the light wave propagating in the l-th medium is... l for:

[0035]

[0036] In the formula, admittance η l for:

[0037]

[0038] Meanwhile, n of each layer in the membrane structure l and θ l It conforms to Snell's Law, that is:

[0039] n l sinθ l =n0sinθ0

[0040] The characteristic matrix M of the D'MD structure all for:

[0041]

[0042] If the air admittance is η0 and the base admittance is η k+1 Then the reflectivity R and transmittance T of the incident surface of the D'MD structure are respectively:

[0043]

[0044] Based on the target requirement of D'MD configuration thin films to achieve both high transparency in visible light and low emissivity in infrared, a film structure performance optimization function Z, as shown in the expression, is constructed to facilitate further optimization design of the film structure.

[0045] Z = T vis (1-ε(T))

[0046] In the formula T vis The visible light integrated transmittance, ranging from 0.38 to 0.78 μm, can be expressed as:

[0047]

[0048] Where T(λ) is the spectral transmittance of the film structure, and D λ Let V(λ) be the relative spectral power distribution of the D65 standard light source, V(λ) be the human eye's visibility coefficient, and ε(T) be the 3–14 μm infrared integrated emissivity, which can be expressed as:

[0049]

[0050] Where R(λ) is the spectral reflectance of the film structure, E λ , b (λ, T) is the blackbody spectral emission power, C1 = 3.742 × 10⁻⁶ 8 W·μm 4 ·m -2 C2 = 1.439 × 10 4 μm·K, temperature T is 300K.

[0051] High-reflectivity films are made of high refractive index n H and low refractive index n L For a periodic multilayer film composed of two materials stacked alternately with an optical thickness of λ / 4, the reflectivities of the odd-numbered 2s+1 high-reflectivity film are as follows:

[0052]

[0053] The wavelength width of the high reflectivity band is:

[0054]

[0055] In the formula, n0 is the refractive index of the incident medium, n g Let n be the refractive index of the substrate material. Equations (1) and (2) show that when the number of periods s is fixed and the refractive indices of the incident medium and the substrate material remain constant, the reflectivity and high-reflection bandwidth of the high-reflection film increase with the refractive index ratio n. H / n L The higher the refractive index ratio, the higher the reflectivity and the wider the reflection bandwidth.

[0056] In the dielectric materials of D'MD thin film structures, materials with a refractive index n of 1.6-4.0 can be used as high refractive index materials (H, such as titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), niobium pentoxide (Nb2O5), zirconium dioxide (ZrO2), yttrium trioxide (Y2O3), hafnium dioxide (HfO2), etc.), while materials with a refractive index n of 1.0-1.6 can be used as low refractive index materials (L, such as silicon dioxide (SiO2), magnesium fluoride (MgF2), etc.). The reflection bandwidth varies with the refractive index ratio n. H / n L The higher the refractive index ratio, the higher the reflectivity and the wider the reflection bandwidth. The intermediate metal layer plays a crucial role in visible light transmission and infrared reflection, and can be made of materials such as silver (Ag), gold (Au), aluminum (Al), and copper (Cu).

[0057] When a laser beam passes through a dielectric thin film, interference occurs between the reflected and incident light. The superposition of this opposing interference between the reflected and incident light results in a standing wave within the dielectric film. The standing wave electric field distribution of a 33-layer TiO2 / SiO2 high-reflectivity film (HL)^16H is shown below. Figure 2 As shown, the standing wave antinodes are located at the film interface, with a maximum intensity of 4n0. 2 / n H 2 And according to the ratio n L 2 / n H 2 The intensity of the standing wave field decreases proportionally, and the intensity decreases further into the membrane layer.

[0058] In the visible and near-infrared regions, the absorption coefficient of high-refractive-index materials is generally one or two orders of magnitude larger than that of low-refractive-index materials, and the interfacial absorption of the film is much greater than the absorption of the film itself. From the distribution of the electric field intensity, it can be concluded that the peak electric field intensity is located at every H / L interface, and according to the ratio n...L 2 / n H 2 Decrease when the refractive index n of a low-refractive-index material L When constant, the refractive index n of high refractive index materials H The larger the value, the faster the peak electric field strength decreases.

[0059] This thin-film structure employs a composite design, with an inner laser-protective film while also achieving overall stealth capabilities. In close-range combat, it can utilize its visible light stealth and laser protection functions; in long-range combat, it can leverage its infrared stealth to evade detector detection; when the target is attacked or damaged, the outer layers (M and D layers) will be damaged first, exposing the inner laser-protective film (D' layer). A comparison of the reflectance spectra before and after the outer layer detaches is shown in the figure. Figure 3 As shown, this design fully leverages the inherent advantages of the thin-film structure, not only improving the overall service life and damage resistance but also significantly enhancing the comprehensive protective performance of stealth equipment. This integrated design effectively solves the problems of traditional stealth materials being easily damaged and lacking in protective performance. Even if the stealth layer is damaged, a smooth transition from "stealth" to "protection" can be achieved, ensuring that the facility can continue to function properly in harsh environments, providing strong support for applications in related fields.

[0060] This invention also proposes a symmetrical DMD'MD thin film structure. Based on the fact that incident light has the same spectral and electric field distribution characteristics when coming from either the front or back of the film system, a dual-band compatible camouflage film can be fabricated into a micro-element mirror, and further into a dual-band compatible camouflage coating material. This material can then be applied to the surfaces of drones, tanks, aircraft, satellites, or other facilities requiring protection via spraying, scraping, or brushing. This structure maintains visible light and infrared stealth and laser protection characteristics and can be widely applied to irregular object surfaces, without being limited by coating equipment or the shape and size of the workpiece.

[0061] To achieve a balance between high visible light transmission, low infrared emission, and high laser reflectivity, this invention proposes novel asymmetric D'MD and symmetric DMD'MD structures, where D' represents a high refractive index n. H and low refractive index n L Multilayer dielectric materials consisting of alternating layers of two dielectric materials, where M represents a metallic material and D represents a dielectric material.

[0062] One of the advantages of this invention is:

[0063] The thin film, designed with this novel D'MD structure, is compatible with both visible and infrared stealth and laser protection, and has the following advantages:

[0064] 1. Compared with traditional structures, the D'MD structure utilizes a high refractive index n H and low refractive index n L The periodic multilayer film formed by alternating stacking of two materials replaces the traditional single-layer dielectric film, which can meet the requirements of multi-band stealth and laser protection compatibility. This capability provides strong protection for the survivability of covert combat equipment and platforms.

[0065] 2. Compared to single-layer metals, the D'MD structure improves visible light transmittance, such as... Figure 4 As shown, the color of the film can be changed by altering the thickness of the metal and the top dielectric layer, exhibiting excellent visible light transparency while also possessing good eye-friendly properties under strong light irradiation.

[0066] 3. When incident at a certain angle (0-45°), the reflectivity is above 90%, the average transmittance of visible light is above 80%, and the average emissivity of infrared light is below 4.5%, exhibiting low angle effect;

[0067] 4. It possesses high-level background perspective reproduction and high-temperature infrared radiation suppression capabilities. While maintaining low emissivity in the infrared band, it also provides important laser protection. This research provides a new approach for the design and application of multi-band compatible stealth and laser protection materials.

[0068] 5. This design uses only three materials, and the manufacturing process is relatively simple. Compared to traditional stealth and protective layers that require stacked membrane layers, it has fewer layers, lower cost, and is more direct and convenient, making it suitable for mass production;

[0069] 6. This film system can be designed with a symmetrical structure, maintaining its visible light and infrared stealth and laser protection characteristics, and can be widely applied to irregular object surfaces. It is not limited by the coating equipment or the shape and size of the workpiece.

[0070] 7. This film system exhibits good robustness, meaning that certain errors during film preparation have minimal impact on its spectral characteristics. A comparison of the initial designed spectrum and the spectrum at an error threshold of 5% is shown in the figure. Figure 5 As shown, the reflectivity of the center wavelength remains above 99%, thus retaining its visible light infrared stealth capability.

[0071] The second advantage of this invention is:

[0072] Based on the basic structure of D'MD, its advantages over conventional camouflage and protective films are as follows:

[0073] 1. When incident normally, the average reflectivity in the 1000-1100nm range is over 99%, and the 50% reflectivity bandwidth is over 250nm, which can achieve laser protection;

[0074] 2. It has a lower average emissivity in the infrared band, which can better reduce the reflection of detection light by detection and sensing technologies, such as infrared detection, lidar, and infrared guidance. It has a better camouflage capability and can achieve "undetectable" or stealth by increasing the detection range.

[0075] 3. With a visible light transmittance of over 85%, its high transmittance in the visible light band makes it transparent in glass windows, inspection windows, lenses, or other optical windows, thus broadening its application scenarios, such as laser protective glasses, fighter jet cockpit canopies, and drone camera protective covers.

[0076] 4. Compared to the most commonly used infrared camouflage metal coatings, the D'MD film exhibits a lower coefficient of friction during scratching compared to single-layer metal. In other words, the D'MD film can withstand friction and abrasion without significantly sacrificing its camouflage performance;

[0077] 5. The membrane system is compatible with multiple bands for stealth and laser protection, and has the characteristics of both camouflage and protective films. It solves the problem of multi-functional compatibility and can effectively deal with the risk of being attacked by laser weapons due to the failure of stealth effect in actual combat.

[0078] Based on the above mechanism, the following will illustrate the process with specific embodiments and experimental data. In this specific embodiment, the thin film can be prepared using physical vapor deposition (PVD) methods, including combinations of different techniques such as ion beam sputtering deposition (IBS), magnetron sputtering deposition (MS), electron beam evaporation (EB), or electron beam evaporation ion-assisted deposition (EBD-IAD). Alternatively, chemical vapor deposition (CVD) or liquid-phase coating methods for pearlescent thin films can also be used to prepare the thin film.

[0079] The substrate material includes polished glass, polished stainless steel, polycarbonate / polymethyl methacrylate (PC / PMMA) composite material, fluoroethyl propylene (FEP), polyvinyl difluoroethylene (PVDF), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinyl butyral (PVB), polyurethane elastomer (TPU), polyimide (PI), polished mirror aluminum, polymethyl methacrylate (PMMA), ethylene vinyl acetate copolymer (EVA), polypropylene (PP), cellulose triacetate (TAC), polytetrafluoroethylene (PTFE), and polyvinyl butyral (PVB). A release layer material is coated on the substrate. These materials can be water-soluble fluorides or chlorides, or water-soluble organic materials and solvents, such as polyvinyl alcohol, acrylic resins, polyvinyl acetate, and chlorides or fluorides. Specifically:

[0080] Example 1

[0081] In this example, the structure of the visible infrared stealth and laser protection compatible film is: D' / M / D.

[0082] The laser protective film has a total of 17 layers and a center wavelength of 1030nm. Here, D represents H, which is the high refractive index material tantalum pentoxide (Ta2O5), M represents the metallic material silver (Ag), D' represents (HL)^7H, L represents the low refractive index material silicon dioxide (SiO2), and (HL)^7H is a stack of 15 reflective films, which together with silver and tantalum pentoxide form the D'MD structure.

[0083] The reflection spectra of the novel D'MD structure compared to those of conventional dielectric / metal / dielectric structures are as follows: Figure 6 As shown, by using a high refractive index n H and low refractive index n L A periodic multilayer film composed of alternating stacks of two materials replaces the traditional single-layer dielectric film, resulting in a reflectance of 99.23% at a center wavelength of 1030 nm, a 50% reflectance bandwidth of 899.17-1208.3 nm, and a 90% reflectance bandwidth of 920.13-1171.6 nm. Furthermore, it maintains an average transmittance of 88.32% in the visible light (380-780 nm) spectrum, and its infrared absorption spectrum is as follows... Figure 7 According to Kirchhoff's laws, the absorptivity of an object is always equal to its emissivity, meaning the intensity of absorbed radiation is equal to the intensity of emitted radiation. The average emissivity in the infrared band (3000-14000nm) is 3.94%, meeting the requirements for visible light stealth, infrared stealth, and laser protection.

[0084] The thickness of each layer of the membrane system in this embodiment is given in Table 1.

[0085] Table 1. Thickness of each layer of the film system (unit: nm)

[0086] Example Layer1 Layer2 Layer 3 Layer 4 Layer 5 Layer 6 1 122.62 176.79 122.62 176.79 122.62 176.79 Layer 7 Layer8 Layer9 Layer 10 Layer11 Layer 12 Layer 13 122.62 176.79 122.62 176.79 122.62 176.79 122.62 Layer 14 Layer 15 Layer 16 Layer 17 176.79 122.62 9 40

[0087] Example 2

[0088] This embodiment uses one example to illustrate the specific preparation method:

[0089] Based on the basic structure of D'MD thin films, different materials, thicknesses, and number of periods will have varying effects on visible light stealth, infrared stealth, and laser protection. By rationally designing the thicknesses of the dielectric and metal layers according to the material properties, a balance point for performance can be achieved. The specific design steps are as follows:

[0090] S1. The high refractive index material and low refractive index material of the reflective film stack have been determined as tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2) respectively. Because silicon dioxide has good optical properties, thermal stability and chemical stability, it is widely used in high-energy laser weapon systems. Tantalum pentoxide has a relatively wide bandgap, low extinction coefficient in the visible and near-infrared bands, and both the materials silicon dioxide and tantalum pentoxide have high laser damage thresholds and excellent anti-laser damage performance.

[0091] S2. Different number of periods affects the laser protection effect. For example Figure 8 , as the number of periods increases, the increment of the reflectivity at the central wavelength of 1030nm gradually decreases (s = 4, R λ＝1030nm = 91.85%, s = 5, R λ＝1030nm = 95.97%, s = 6, R λ＝1030nm = 98.01%, s = 7, R λ＝1030nm = 99.02%, s = 8, R λ＝1030nm = 99.50%, s = 9, R λ＝1030nm = 99.74%). Considering the preparation difficulty of the thin film, the basic number of periods s = 7, the central wavelength λ = 1030nm, and the thickness of each material is the optical thickness of λ / 4 are finally determined.

[0092] S3. When selecting the intermediate functional layer, we consider that the absorption rate of silver (Ag) thin film in the visible light band is less than 5%, with low intrinsic loss and high conductivity, and at the same time has high infrared reflectivity in a wide band. The infrared reflectivity is proportional to the conductivity of the metal layer. Assuming n (refractive index) << k (extinction coefficient) in the solar infrared wavelength region, we can obtain the following formula:

[0093]

[0094] Where μ is the magnetic permeability, c is the speed of light in vacuum, ρ is the resistivity, and τ is the average free time between carrier collisions. Since the magnetic permeability of non-ferromagnetic metals is basically constant, its influence on the reflectivity can be ignored. Materials with high τ and low ρ will exhibit high reflectivity. The resistivity of the material depends on the thickness and surface morphology. For metals at room temperature, silver has the lowest resistivity ρ and the highest average free time τ, indicating the highest reflectivity. Therefore, the silver film layer is considered the most suitable choice for the intermediate metal in the D’MD structure.

[0095] S4. When the silver film is too thin, it is difficult to grow it as a continuous film. Silver undergoes electroosmosis at 3 nm, which greatly increases the conductivity. In the 3-5 nm range, nanoparticles aggregate and fuse together. Once a dense, continuous film is formed, the film resistance does not change significantly, and the film can exhibit low emissivity in the infrared band. Therefore, this film has a low threshold at 6 nm.

[0096] As the silver layer thickness increases, the transmittance exhibits a significant linear decrease. When the silver film thickness reaches 20 nm, both reflection and absorption in the visible light band increase significantly, thus affecting the transmittance performance. Therefore, a silver film thickness between 6-20 nm yields optimal results. While all thicknesses are potential candidates for visible-infrared compatibility, a thickness of 9 nm is optimal because it lacks plasma-induced coloration, which negatively impacts transmittance, making it the best choice for applications requiring high visibility and low infrared emissivity. A well-designed balance between the dielectric and metal layer thicknesses can achieve a optimal performance balance.

[0097] S5. As the thickness of the top tantalum pentoxide (Ta2O5) dielectric layer increases, the transmittance in the mid-wavelength range gradually decreases, while the transmittance in the long and short wavelengths gradually increases. Furthermore, a redshift occurs in the transmission peak at the long wavelength, causing the visible light transmission spectrum curve to flatten, thus broadening the high-transmittance radio frequency domain. Simultaneously, as the thickness of the top tantalum pentoxide layer increases, the average visible light transmittance initially increases and then gradually decreases. Overall, a top tantalum pentoxide layer with a thickness of 30–50 nm exhibits good transmittance across the entire visible light band and shows good equivalent admittance matching with the D'MD film structure composed of a 6–15 nm thick Ag film, resulting in a significant induced transmission effect. In addition, as the thickness of the top tantalum pentoxide film increases, the optical path difference due to light interference in the film structure increases, causing the transmission peak to shift towards the long wavelength direction.

[0098] Example 3

[0099] Based on the basic structure of D'MD thin films, different materials, thicknesses, number of periods, and designs with different center wavelengths can be used to achieve broadband or narrowband protection with varying reflection bandwidths and protective effects. The reflection bandwidth varies with the refractive index ratio n. H / n L The larger the refractive index ratio, the higher the reflectivity and the wider the reflection bandwidth. A laser protection dual-band compatible camouflage film designed for the near-infrared laser band of 1064nm has the structure: D'MD.

[0100] This laser-protective film has a total of 19 layers. The selected center wavelength of the reflection band is 1064nm. Here, D represents H, which is the high-refractive-index material titanium dioxide (TiO2), M represents the metallic material aluminum (Al), D' represents (HL)^8H, and L represents the low-refractive-index material magnesium fluoride (MgF2). (HL)^8H is a stack of 17 reflective layers, which, together with aluminum and titanium dioxide, form a D'MD structure. The average transmittance in the visible light band of 400-780nm is 75.69%, the reflectance at 1064nm under normal incidence is 99.94%, and the average emissivity in the infrared band of 3000-14000nm is 11%. It can simultaneously achieve infrared stealth, visible light stealth, and laser protection.

[0101] The visible-infrared stealth and laser protection compatible film shown in this embodiment has a wider reflectance bandwidth, with a 50% reflectance bandwidth of 874.58-1252.6 nm and a 90% reflectance bandwidth of 885.24-1231.4 nm. This effectively addresses the issue of reflectance degradation at angled incidence, maintaining a reflectance above 90% at certain angles (0-40°), an average visible light transmittance above 70%, and an average infrared emissivity below 9%. The thicknesses of each layer in the film system are given in Table 2.

[0102] Table 2. Thickness of each layer of the film system (unit: nm)

[0103] Example Layer1 Layer2 Layer 3 Layer 4 Layer 5 Layer 6 3 115.30 189.27 115.30 189.27 115.30 189.27 Layer 7 Layer8 Layer9 Layer 10 Layer11 Layer 12 Layer 13 115.30 189.27 115.30 189.27 115.30 189.27 115.30 Layer 14 Layer 15 Layer 16 Layer 17 Layer 18 Layer 19 189.27 115.30 189.27 115.30 9 30

[0104] Example 4

[0105] A symmetrical visible-infrared stealth and laser protection compatible thin film has the structure: D / M / D' / M / D. This laser protection thin film has a total of 19 layers, where D represents H (zirconium dioxide, ZrO2), M represents gold (Au), D' is represented by (HL)^7H, and L represents magnesium fluoride (MgF2), a low-refractive-index material. The physical thicknesses of each layer are given in Table 3.

[0106] Table 3. Thickness of each layer of the film system (unit: nm)

[0107] Example Layer1 Layer2 Layer 3 Layer 4 Layer 5 Layer 6 4 31 10 130.71 192.71 130.71 192.71 Layer 7 Layer8 Layer9 Layer 10 Layer11 Layer 12 Layer 13 130.71 192.71 130.71 192.71 130.71 192.71 130.71 Layer 14 Layer 15 Layer 16 Layer 17 Layer 18 Layer 19 192.71 130.71 192.71 130.71 10 31

[0108] The camouflage film, which is compatible with both visible and infrared dual-band stealth and laser protection, is designed with a symmetrical structure. It has the same spectral characteristics and electric field distribution characteristics for incident light from either the front or back of the film system. Therefore, the dual-band compatible camouflage film can be fabricated into a micro-element mirror, and then into a dual-band compatible camouflage coating material. This material can then be coated onto the surface of drones, tanks, aircraft, satellites, or other facilities that need protection by means of spraying, scraping, or brushing.

[0109] For a normally incident 1064nm laser, its reflectivity is 99.11%, its average transmittance in the 400-780nm visible light band is 63.16%, and its average emissivity in the 3000-14000nm infrared band is 10.56%, enabling infrared and visible light stealth and laser protection.

[0110] This embodiment provides a symmetrical visible light infrared stealth and laser protection compatible thin film and its design method. While maintaining visible light infrared stealth and laser protection, it can be widely used on irregular object surfaces and is not limited by coating equipment and workpiece shape and size.

[0111] Example 5

[0112] Based on the D'MD basic structure, different visible light reflectivities are obtained by changing the thickness of the top layer, thus achieving different colors. The structure is: D' / M / D

[0113] The laser protective film has a total of 19 layers. The center wavelength of the selected reflection band is 1030nm. Here, D represents H, which is the high refractive index material hafnium dioxide (HfO2), M represents the metallic material gold (Au), D' is represented by (HL)^8H, L represents the low refractive index material silicon dioxide (SiO2), and (HL)^8H is a stack of 17 reflective films, which together with silver and hafnium dioxide form the D'MD structure.

[0114] By adjusting the thickness of the top hafnium dioxide film (20-200 nm) to control the reflection in the visible spectrum, the designed structure can exhibit different colors, as shown in the CIE 1931 chromaticity diagram. Figure 9 As shown in Table 4, the film maintains a reflectivity of over 97% at 1030nm under normal incidence, and an average emissivity of less than 9% in the infrared band (3000-14000nm). Changing the D thickness does not affect the laser protection and infrared stealth effects. The visible light transmittance of the film remains above 80%, and it exhibits a slight tint, which is beneficial for shielding unwanted sunlight from aircraft windows and other equipment optical windows. Therefore, the D'MD film not only possesses excellent visible light transparency and good eye-friendliness under strong light, but also provides infrared stealth and laser protection. The physical thicknesses of each layer are given in Table 4.

[0115] Table 4. Thickness of each layer of the film system (unit: nm)

[0116] Example Layer1 Layer2 Layer 3 Layer 4 Layer 5 Layer 6 5 140.31 181.98 140.31 181.98 140.31 181.98 Layer 7 Layer8 Layer9 Layer 10 Layer11 Layer 12 Layer 13 140.31 181.98 140.31 181.98 140.31 181.98 140.31 Layer 14 Layer 15 Layer 16 Layer 17 Layer 18 Layer 19 181.98 140.31 181.98 140.31 10 20-200

[0117] Example 6

[0118] Based on the D'MD basic structure, different visible light reflectivities are obtained by changing the metal thickness, thus achieving different colors. The structure is as follows:

[0119] D' / M / D

[0120] The laser-protective film has a total of 19 layers, with the selected center wavelength of the reflection band at 1030 nm. Here, D represents H, which is the high-refractive-index material yttrium trioxide (Y₂O₃), M represents the metallic material silver (Ag), D' represents the stacking medium (HL)₈H, and L represents the low-refractive-index material silicon dioxide (SiO₂). (HL)₈H is a stack of 17 reflective layers, forming a D'MD structure with silver and yttrium trioxide. As the Ag layer thickness increases from 2 nm to 15 nm, the color changes from blue to yellowish-brown, and then to transparent. This phenomenon can be attributed to the Volmer-Weber mode growth of the silver layer at a thinner thickness, leading to nanoparticle formation and cracks, resulting in localized surface plasmon resonance and multiple scattering effects, causing color changes due to interaction with light. This effect is mitigated when the separated nanoparticles connect and grow to form a dense film.

[0121] Surface plasmon polaritons (SPPs) can be excited at the interface between the dielectric and the metal, effectively concentrating the electric field. D'MD thin films can significantly compress free-space wavelengths, thereby enhancing transmission. The electric field distribution shows that the upper and lower surfaces of Ag support the SPPs asymmetrically, leading to faster energy degradation in the horizontal direction. Therefore, when the photon energy is unsuitable for exciting SPPs, the field concentration capability decreases, the surface electromagnetic field dissipates rapidly, and transparency deteriorates.

[0122] Therefore, the color change of the film is mainly attributed to plasmonic resonance absorption caused by the island-like growth of the ultrathin silver layer, resulting in low infrared absorption and increased transmission, rather than simply the thickness. The visible light transmittance of the film can consistently remain above 90%, and it exhibits a slight tint, which is beneficial for shielding unwanted sunlight from aircraft windows and other equipment optical windows. Thus, the D'MD film not only possesses excellent visible light transparency and good eye-care properties under strong light, but also offers infrared stealth and laser protection. The physical thicknesses of each layer are given in Table 5.

[0123] Table 5. Thickness of each layer of the film system (unit: nm)

[0124] Example Layer1 Layer2 Layer 3 Layer 4 Layer 5 Layer 6 4 149.46 181.98 149.46 181.98 149.46 181.98 Layer 7 Layer8 Layer9 Layer 10 Layer11 Layer 12 Layer 13 149.46 181.98 149.46 181.98 149.46 181.98 149.46 Layer 14 Layer 15 Layer 16 Layer 17 Layer 18 Layer 19 181.98 149.46 181.98 149.46 2-20 40

[0125] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A laser thin film structure, characterized in that, The thin film structure is a first dielectric layer / metal layer / second dielectric layer / substrate layer, wherein the second dielectric layer is formed by alternating deposition of a low refractive index dielectric material and a high refractive index dielectric material; the structure expression of the second dielectric layer is H(LH)^s, where H represents a high refractive index dielectric material with an optical thickness of λ / 4, L represents a low refractive index dielectric material with an optical thickness of λ / 4, and s represents the number of film system periods.

2. The laser thin film structure as described in claim 1, characterized in that, The high-refractive-index medium material has a refractive index of 1.6-4.0; The low-refractive-index medium material has a refractive index of 1.0-1.

6.

3. A laser thin film structure as described in claim 1 or 2, characterized in that, The high refractive index dielectric material includes one or more of the following: titanium dioxide, tantalum pentoxide, aluminum oxide, niobium pentoxide, zirconium dioxide, yttrium oxide, and hafnium dioxide; The low-refractive-index dielectric material includes one or more of silicon dioxide and magnesium fluoride.

4. The laser thin film structure as described in claim 1, characterized in that, The material of the metal layer includes one or more of the following: silver, gold, aluminum, and copper.

5. A laser thin film structure, characterized in that, The thin film structure is a first dielectric layer / first metal layer / second dielectric layer / second metal layer / third dielectric layer, wherein the second dielectric layer is formed by alternating deposition of a low refractive index dielectric material and a high refractive index dielectric material; the structure expression of the second dielectric layer is H(LH)^s, where H represents a high refractive index dielectric material with an optical thickness of λ / 4, L represents a low refractive index dielectric material with an optical thickness of λ / 4, and s represents the number of film system periods.

6. The laser thin film structure as described in claim 5, characterized in that, The high-refractive-index medium material has a refractive index of 1.6-4.0; The low-refractive-index medium material has a refractive index of 1.0-1.

6.

7. A laser thin film structure as described in claim 5 or 6, characterized in that, The high refractive index dielectric material includes one or more of the following: titanium dioxide, tantalum pentoxide, aluminum oxide, niobium pentoxide, zirconium dioxide, yttrium oxide, and hafnium dioxide; The low-refractive-index dielectric material includes one or more of silicon dioxide and magnesium fluoride.

8. A laser thin film structure as described in claim 5, characterized in that, The material of the metal layer includes one or more of the following: silver, gold, aluminum, and copper.

9. A method for preparing a laser thin film structure, characterized in that, This method is used to prepare the thin film structure as described in any one of claims 1-8; High refractive index material, low refractive index material, and metal layer material are selected; the number of film system cycles is determined based on the number of cycles in which the reflectivity of the thin film to the center wavelength within the reflection band is greater than or equal to 99% and the difficulty of thin film preparation; the thin film is prepared by deposition based on the parameters determined above.

10. The method for preparing a laser thin film structure as described in claim 9, characterized in that, The metal layer material is silver; the thickness of the metal layer material is 6-15 nm; the material of the first dielectric layer is tantalum pentoxide; the thickness of the first dielectric layer material is 30-50 nm.

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