Laser film structure and preparation method thereof

Abstract

The invention discloses a laser film structure and a preparation method thereof. Wherein the thin film structure comprises a first dielectric layer, a metal layer, a second dielectric layer and a base material layer, and the second dielectric layer is formed by alternately depositing a dielectric material with a low refractive index and a dielectric material with a high refractive index; the structural expression of the second dielectric layer is H (LH) s, H represents a high-refractive-index dielectric material with the optical thickness of lambda / 4, L represents a low-refractive-index dielectric material with the optical thickness of lambda / 4, and s represents the number of cycles of the film system. According to the invention, the camouflage capability is improved, and the excellent laser protection performance is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of laser thin films, and in particular to an improved DMD thin film. Background Art

[0002] With the rapid development of various detection technologies, single-band stealth material technology has been unable to meet the needs of evading detection, identification and attack. Multi-spectrum compatible stealth materials have become an inevitable development trend. Camouflage technology is crucial in protecting military equipment and is widely used in various types of military equipment (aircraft, ships, tanks, artillery vehicles and armored vehicles, etc.). The design of multi-spectrum compatible stealth materials usually has technical bottlenecks due to conflicts in stealth principles in different frequency bands. For example, the spectral response requirements such as low infrared emission and high visible light perspective have opposite mutual constraints. Current detection technology tends to be multi-source and multi-mode combined, and multi-band compatible camouflage is particularly important.

[0003] In order to meet the requirements of multi-band compatible camouflage, camouflage technologies such as Fabry-Perot (FP) cavity, photonic crystal, metasurface, and multilayer optical coating have been proposed. Patent CN106383376A proposes a multilayer thin film structure infrared stealth material based on YbF3 and ZnSe materials, which can achieve low emissivity in the infrared band, thereby achieving an effective infrared stealth effect and compatible with radar stealth. Patent CN112346162B proposes a metal-dielectric spectrally selective multi-band stealth film, which achieves compatible stealth in the mid-infrared band and 1.064um laser wavelength through alternating superposition of Si layers and W layers. These technologies effectively control the absorption or reflection of electromagnetic waves of specific wavelengths by introducing nanostructures. However, most multi-band compatible camouflage films are concentrated in the long-wave band, and their appearance presents opaque or dark characteristics due to the presence of lossy materials and resonant absorption cavities.

[0004] In order to reduce the detection signal intensity of the device, it is necessary to deal with the problems of infrared emissivity, microwave reflection loss and laser absorption. At present, the research on optical window camouflage with high transmittance in the visible light band and low emissivity in the infrared band is not sufficient. The essence of this camouflage is to improve the impedance matching in the visible light band, thereby guiding more light into the film instead of reflecting it back, and ensuring that the film blocks infrared radiation at the atmospheric window. To improve the camouflage performance of the optical window, it is necessary to achieve high transmittance in the wavelength range of 380-780nm, and it is necessary to suppress infrared signals to reduce the radiation temperature of the target surface. In addition, these features are expected to be combined with visible camouflage coatings or devices to expand their infrared camouflage functions. However, with the improvement of infrared camouflage performance, it will inevitably lead to a decrease in visible light transparency.

[0005] The dielectric / metal / dielectric structure is similar to a sandwich, where two dielectric layers are used to achieve high transmittance through optical interference and near-perfect impedance matching with free space. In addition, the integrated metal layer is essential to provide enhanced conductivity, thereby suppressing infrared thermal emission. Although a thicker metal layer may result in low infrared emissivity, it may also reduce visible light transmittance due to its reflective properties. Conversely, ultra-thin metal layers can lead to increased infrared emissivity caused by high plasma resonance absorption, and may also lead to reduced conductivity. Current dielectric / metal / dielectric structures are mostly limited to transparent conductive films used in optoelectronic devices. By embedding a highly reflective metal layer between two dielectric layers, the structure can suppress the visible light reflection properties from the metal layer, achieving a selective transmission enhancement effect.

[0006] In addition, in the complex and ever-changing battlefield environment of modern times, equipment faces threats from various detection and attack methods such as vision, infrared and laser. If it only has stealth function but lacks effective protection ability, the equipment will be extremely vulnerable to destructive attacks once it is detected, and its survivability will be greatly reduced. The technology with both stealth and protection enables the equipment to resist various weapon attacks even if it is detected, thereby significantly improving the overall survivability. Traditional laser protection materials usually use metals, ceramics or polymer composite materials, which mainly rely on strong absorption and scattering to suppress the incident laser, thereby protecting the lower equipment from damage. Patent CN108803182A proposes a laser protection film, which has good laser protection effect based on the characteristics of liquid crystal polymer materials, and has the advantages of large protection angle and good flexibility. Patent CN207164389U discloses a laser goggles, which blocks harmful blue light and infrared light through a multi-layer film structure, and absorbs ultraviolet rays with reflected light to achieve the purpose of protecting glasses. However, although this protection mechanism based mainly on energy absorption is effective in preventing laser damage to the target, it also faces the problem that its optical properties are difficult to meet the stealth requirements.

[0007] Therefore, in order to deal with 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 the present invention is to propose a laser film structure and a preparation method thereof, which can improve the camouflage ability while ensuring excellent laser protection performance.

[0009] According to one aspect of the present invention, a laser thin film structure is provided, which 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 second dielectric layer structure is expressed as H(LH)^s, wherein 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 film has high visible light transparency, low infrared emissivity, and excellent laser protection. It can be attached to the camouflage coating surface of special vehicles to achieve infrared and visible light stealth and protection compatibility, and can be used for cockpit windows to ensure that the field of vision is not affected to achieve the effects of heat insulation, temperature control and infrared stealth.

[0011] In some embodiments, the high refractive index dielectric material has a refractive index of 1.6-4.0;

[0012] The refractive index of the low-refractive-index dielectric material is 1.0-1.6.

[0013] In the above technical solution, among the dielectric materials of the D'MD thin film structure, the refractive index n in the range of 1.6-4.0 can be used as high refractive index material 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.), and the refractive index n in the range of 1.0-1.6 can be used as low refractive index material L (such as silicon dioxide (SiO2), magnesium fluoride (MgF2), etc.), and 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 vital role in visible light transmission and infrared reflection, and silver (Ag), gold (Au), aluminum (Al), copper (Cu) and the like may be selected.

[0016] According to another aspect of the present invention, a laser thin film structure is provided, which 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 second dielectric layer structure is expressed as H(LH)^s, wherein 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 above-mentioned thin film structure;

[0018] Select high refractive index materials, low refractive index materials and metal layer materials; determine the number of film system periods according to the number of periods in which the reflectivity of the film to the central wavelength in the reflection band is greater than or equal to 99% and the difficulty of preparing the film; prepare the film by deposition method based on the above-determined parameters.

[0019] In the above technical solution, at normal incidence, the average reflectivity at 1000-1100nm is more than 99%, and the 50% reflectivity bandwidth is more than 250nm, which can achieve laser protection. Therefore, when selecting the number of periods here, it is necessary to consider that the reflectivity of the central wavelength is always maintained above 99%, and determine the optional number of periods on this premise, and then further determine the final number of periods based on the difficulty of preparation. The preparation of thin films can be achieved by physical vapor deposition (PVD) methods, including ion beam sputtering deposition (IBS), magnetron sputtering deposition (MS), electron beam evaporation (EB) or electron beam evaporation ion assisted deposition (EBD-IAD) and other different technologies. In addition, chemical vapor deposition (CVD) methods or pearlescent thin film liquid phase coating methods can also be used to prepare thin films. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 Schematic diagram of D'MD film structure (left) and DMDMD' film structure (right);

[0022] Figure 2 The standing wave electric field distribution diagram of 33-layer TiO2 / SiO2 high reflective film (HL)^16H;

[0023] Figure 3This is a comparison of the reflection spectra before and after the outer layer of the D'MD film falls off;

[0024] Figure 4 Comparison of visible light transmission spectra of D'MD structure and single-layer metal;

[0025] Figure 5 This is a comparison chart of the initial design spectrum of the film and the spectrum when the error threshold is 5%;

[0026] Figure 6 The comparison diagram of the reflection spectra of the D'MD structure and the conventional dielectric / metal / dielectric structure;

[0027] Figure 7 An infrared absorption spectrum diagram of a structure of a visible light infrared stealth and laser protection compatible film in one embodiment;

[0028] Figure 8 A comparison diagram of the reflection spectrum of a structure of a visible light infrared stealth and laser protection compatible film as it changes with period in one embodiment;

[0029] Fig. 9 This is the representation of the film color of Example 5 as the top dielectric thickness changes (20-200nm) in the CIE 1931 chromaticity diagram. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Similarly, the following examples are only partial embodiments of the present invention rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0031] The present invention provides a laser film structure and a preparation method thereof, which can improve the camouflage capability while ensuring excellent laser protection performance. The specific mechanism is as follows:

[0032] The D'MD structure is a composite optical film. Among them, the laser protection part needs to have high reflectivity and excellent resistance to laser damage. The basic structure of the high-reflective film is H(LH)^s (H is a high refractive index material, L is a low refractive index material, and s is the film period). The reflectivity of the central wavelength in the reflection band is generally not less than 99%. The stealth part is based on the Stefan-Boltzmann law and Kirchhoff's law. The infrared high reflectivity layer can reduce the surface emissivity, thereby effectively suppressing the thermal radiation of the target and reducing the radiation difference between the target and the environment, so that the infrared detector cannot or is not easy to detect the target. In the visible light band, visible light stealth can be achieved by increasing the transmittance and cooperating with camouflage coatings and electrochromic.

[0033] Metals have mirror properties and can effectively block the propagation of electromagnetic waves, making them ideal materials for suppressing infrared signals. However, the high extinction coefficient of most metals, coupled with their high reflectivity in the optical band, makes them unfavorable for achieving the desired transparent appearance. Metal films such as Au, Ag, and Cu show 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 the upper and lower sides of the metal film, the inner side is made of a high refractive index n H and low refractive index n L The periodic multilayer film is formed by alternating two materials. The dielectric film system on both sides can suppress the visible light reflection characteristics from the metal layer, achieving a selective transmission enhancement effect. For the dielectric layer, they play an important role in changing the impedance to induce more light to be transmitted to the film, which requires them to have high transparency and suitable refractive index. Figure 1 The 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 the symmetrical (D'MDMD') structure are shown. The D'MD structure has the high visible light transmittance and low infrared emissivity characteristics of the traditional dielectric / metal / dielectric structure, while being compatible with excellent laser protection. By designing the film material system, we can obtain the best optical performance and achieve the synergistic gain of optical effects such as visible light transmission induction, infrared radiation suppression, and laser high reflection.

[0034] According to the thin film optical theory, the transfer matrix theory calculation method is used to analyze the influence mechanism of D'MD structural characteristics on visible light transmission and infrared reflection spectra. If a light wave with a wavelength of λ enters the composite thin film structure from the air layer with a refractive index of n0 at an incident angle θ0, the light wave transmitted in the thin film dielectric layer can be regarded as the superposition of the downlink wave and the uplink wave. l , n l ,θ l When are the thickness, refractive index and refraction angle of the lth layer of medium respectively, the characteristic matrix M of the light wave transmitted in the lth layer of medium is l for:

[0035]

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

[0037]

[0038] At the same time, the n of each layer in the film structure l and θ l It complies with 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, the base admittance is η k+1 , then the reflectivity R and transmittance T of the incident D'MD structure surface are:

[0043]

[0044] According to the target requirements of D'MD configuration film for high visible light transparency and low infrared radiation dual function compatibility, a film structure performance optimization function Z shown in the expression is constructed to facilitate further optimization design of its film structure:

[0045] Z=T vis (1-ε(T))

[0046] Where T vis It is the integrated transmittance of visible light from 0.38 to 0.78 μm, which can be expressed as:

[0047]

[0048] Where T(λ) is the spectral transmittance of the film structure, D λ is the relative spectral power distribution of the D65 standard light source, V(λ) is the visual coefficient of the human eye; ε(T) is the 3-14μm 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 8 W·μm 4 ·m -2 , C2=1.439×10 4 μm·K, the temperature T is 300K.

[0051] High reflective film is made of high refractive index n H and low refractive index n L The periodic multilayer film formed by alternating two materials with an optical thickness of λ / 4 has a reflectivity of:

[0052]

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

[0054]

[0055] Where n0 is the refractive index of the incident medium, n g is the refractive index of the substrate material. Equations (1) and (2) show that when the period number s is fixed and the refractive index of the incident medium and the substrate material remains unchanged, the reflectivity and high reflection bandwidth of the high reflection film increase with the refractive index ratio n. H / n L That is to say, the larger the refractive index ratio, the higher the reflectivity and the wider the reflection bandwidth.

[0056] In the dielectric materials of D'MD thin film structure, the refractive index n between 1.6 and 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.), and the refractive index n between 1.0 and 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 refractive index ratio n. H / n L The larger the refractive index ratio, the higher the reflectivity and the wider the reflection bandwidth. The intermediate metal layer plays a vital role in visible light transmission and infrared reflection, and can be selected from silver (Ag), gold (Au), aluminum (Al), copper (Cu), etc.

[0057] When the laser passes through the dielectric film, interference occurs between the reflected light and the incident light. The result of the interference superposition between the reflected light and the incident light is the formation of standing waves in the dielectric film. The standing wave electric field distribution of a 33-layer TiO2 / SiO2 high reflective film (HL)^16H is shown in the figure. Figure 2 As shown, the standing wave antinode is at the membrane interface, and the maximum intensity is 4n0 2 / n H 2 , and by ratio n L 2 / n H 2 It decreases proportionally, and the deeper into the membrane layer, the smaller the standing wave field strength.

[0058] In the visible light region and near infrared region, 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 interface absorption of the film layer is much larger than the absorption of the film layer itself. From the distribution of electric field intensity, it can be concluded that the peak value of electric field intensity is located at each H / L interface, and the ratio nL 2 / n H 2 decreases when the refractive index n of the low refractive index material L When the refractive index of the high refractive index material n is constant, H The larger it is, the faster the peak value of the electric field strength decreases.

[0059] The film structure adopts a composite design, with the inner layer being a laser protection film, and the whole can also achieve stealth function. In close-range combat, its visible light stealth and laser protection functions can be used; in long-range combat, its infrared stealth effect can be used to avoid detector reconnaissance; when the target is hit or damaged, the outer layer (M layer and D layer) will be damaged first, exposing the inner laser protection film (D' layer). The reflection spectrum comparison before and after the outer layer falls off is shown in the figure below. Figure 3 As shown. The inherent advantages of the film structure are fully utilized, which not only improves the overall service life and damage resistance, but also greatly enhances the comprehensive protection performance of the stealth equipment. This integrated design can effectively solve the problem that traditional stealth materials are easily damaged and lack protection performance. Even if the stealth layer is damaged, it can achieve a smooth transition from "stealth" to "protection", ensuring that the facility can continue to perform its due functions in harsh environments, providing strong guarantees for applications in related fields.

[0060] The present invention also proposes a symmetrical DMD'MD film structure, which has the same spectral characteristics and electric field distribution characteristics when the incident light comes from the front or back of the film system, so that the dual-band compatible camouflage film can be prepared into a micro-element reflector, and then prepared into a dual-band compatible camouflage coating material, which can be applied to the surface of drones, tanks, aircraft, satellites or other facilities that need to be protected by spraying, scraping, brushing, etc. This structure can maintain the characteristics of visible light infrared stealth and laser protection, and can be widely used on irregular object surfaces, without being limited by coating equipment and the shape and size of workpieces.

[0061] In order to take into account the performance of high visible light transmittance, low infrared emission and high laser reflection, the present invention proposes a new structure of asymmetric D'MD and symmetric DMD'MD, where D' represents a high refractive index n H and low refractive index n L A multilayer dielectric material in which two dielectric materials are alternately stacked. M represents metal material and D represents dielectric material.

[0062] One of the benefits of the present invention is:

[0063] The D'MD new structure design of visible light infrared stealth and laser protection compatible film has the following advantages:

[0064] 1. Compared with the traditional structure, the D'MD structure uses a high refractive index n H and low refractive index n L The periodic multilayer film formed by alternating 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 a strong guarantee for the survivability of concealed combat equipment and platforms.

[0065] 2. Compared with single-layer metal, D'MD structure improves visible light transmittance, such as Figure 4 As shown, by changing the thickness of the metal and top dielectric layers, the color of the film can be changed, and while having excellent visible light transparency, it also has good eye-friendly properties under strong light illumination;

[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 infrared emissivity is below 4.5%, with low angle effect;

[0067] 4. It has a high level of background perspective reproduction and high-temperature infrared radiation suppression capabilities. While having a low emissivity in the infrared band, it also has 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 preparation process is relatively simple. Compared with the traditional stealth layer and protective layer stacking, the number of film layers is less, the cost is low, it is more direct and convenient, and it is suitable for large-scale production;

[0069] 6. The film system can be designed as a symmetrical structure, which can maintain the characteristics of visible light infrared stealth and laser protection, and can be widely used on irregular object surfaces. It is not limited by the coating equipment and the shape and size of the workpiece;

[0070] 7. The film system has good robustness, that is, the error in the film preparation process has little effect on the spectral characteristics of the film system. The comparison between the initial design spectrum of the film and the spectrum when the error threshold is 5% is shown in the figure below. Figure 5 As shown, the reflectivity of the central wavelength always remains above 99%, and it still has the visible light infrared stealth function;

[0071] The present invention is beneficial in two aspects:

[0072] Based on the basic structure of D'MD, compared with conventional camouflage films and protective films, its beneficial effects are as follows:

[0073] 1. At normal incidence, the average reflectivity at 1000-1100nm is over 99%, and the 50% reflectivity bandwidth is over 250nm, which can achieve laser protection;

[0074] 2. The average emissivity in the infrared band is lower, which can better reduce the reflection of detection light of detection and perception technology, such as infrared detection, laser radar, infrared guidance, etc., and has better camouflage ability, achieving "undetectable" or increasing the detection distance of stealth;

[0075] 3. The transmittance of visible light remains above 85%. The high transmittance in the visible light band makes it transparent in glass windows, inspection windows, lenses or other optical windows, and its application scenarios are more extensive, such as laser protective glasses, fighter cockpit covers, drone camera protective covers, etc.

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

[0077] 5. The film system has multi-band compatibility with stealth and laser protection, and has the characteristics of camouflage film and protective film, which 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 be explained with specific examples and experimental data. In this specific embodiment, the preparation of the film can be achieved by physical vapor deposition (PVD) method, including ion beam sputtering deposition (IBS), magnetron sputtering deposition (MS), electron beam evaporation (EB) or electron beam evaporation ion assisted deposition (EBD-IAD) and other different technologies. In addition, the chemical vapor deposition (CVD) method or the pearlescent film liquid phase coating method can also be used to prepare the film.

[0079] The substrate material is made of polished glass, polished stainless steel, polycarbonate / polymethyl methacrylate composite material (PC / PMMA), fluoroethyl propylene (FEP), polyvinyl difluoride (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), triacetyl cellulose (TAC), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB). A release layer material is coated on the substrate, and these materials can be fluorides and chlorides that are easily soluble in water, or organic materials and organic solvents that are soluble in water, such as polyvinyl alcohol, acrylic resin, polyvinyl acetate, and chlorides or fluorides. The details are as follows:

[0080] Embodiment 1

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

[0082] The laser protection film has a total of 17 layers and a central wavelength of 1030nm. Here D represents H, which is a high refractive index material tantalum pentoxide (Ta2O5), M represents a metal material silver (Ag), D' represents (HL)^7H, and L represents a low refractive index material silicon dioxide (SiO2). (HL)^7H is a 15-layer reflective film stack, which forms a D'MD structure with silver and tantalum pentoxide.

[0083] The reflectance spectrum of the new D'MD structure compared with the conventional dielectric / metal / dielectric structure is as follows Figure 6 As shown, by using a high refractive index n H and low refractive index n L The periodic multilayer film formed by alternating the two materials replaces the traditional single-layer dielectric film, making the reflectivity at the central wavelength of 1030nm 99.23%, the 50% reflectivity bandwidth of 899.17-1208.3nm, the 90% reflectivity bandwidth of 920.13-1171.6nm, and maintaining the average transmittance of 88.32% in the visible light (380-780nm). The infrared absorption spectrum is as follows Figure 7 According to Kirchhoff's law, the absorptivity of an object is always equal to its emissivity, that is, the intensity of the absorbed radiation is equal to the intensity of the emitted radiation. The average emissivity in the infrared band (3000-14000nm) is 3.94%, which meets the requirements of visible light stealth, infrared stealth and laser protection.

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

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

[0086] Example Layer1 Layer2 Layer3 Layer4 Layer5 Layer6 1 122.62 176.79 122.62 176.79 122.62 176.79 Layer7 Layer8 Layer9 Layer10 Layer11 Layer12 Layer13 122.62 176.79 122.62 176.79 122.62 176.79 122.62 Layer14 Layer15 Layer16 Layer17 176.79 122.62 9 40

[0087] Embodiment 2

[0088] This embodiment takes one of the embodiments as an example to explain the specific preparation method:

[0089] Based on the basic structure of D'MD film, choosing different materials, different thicknesses, and different number of cycles will have different effects on visible light stealth, infrared stealth, and laser protection. According to the characteristics of the material, the thickness of the dielectric layer and the metal layer can be reasonably designed to achieve a balance point of performance balance. 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 of silicon dioxide and tantalum pentoxide have high laser damage thresholds and excellent anti-laser damage performance.

[0091] S2. Different numbers of periods affect the laser protection effect. For example, Figure 8 , as the number of periods increases, the increment of the reflectivity at the central wavelength of 1030 nm 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 = 1030 nm, 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 thickness of the silver film layer is too thin, it is difficult to grow in the form of a continuous film. Silver undergoes electrical permeation at 3nm, which greatly improves the conductivity, while in the range of 3-5nm, the nanoparticles coalesce and fuse with each other. Once a dense, continuous film is formed, the film resistance does not change significantly, and the film can show low emissivity in the infrared band. Therefore, the film has a lower threshold at 6nm.

[0096] As the thickness of the silver layer increases, the transmittance shows a clear linear decay. When the silver film layer increases to 20nm, the reflection and absorption in the visible light band will be significantly enhanced, thus affecting the light transmission performance. Therefore, the thickness of the silver film layer is between 6-20nm to obtain the best effect. Although all thicknesses are potential candidates for visible-infrared compatibility, 9nm thickness is optimal because it lacks plasma-induced coloring, which negatively affects transmittance, making it the best choice for applications that require high visibility and low infrared emissivity. Reasonable design of the thickness of the dielectric layer and the metal layer can achieve a balance point of performance balance.

[0097] S5. With the increase of the thickness of the top dielectric layer of tantalum pentoxide (Ta2O5), the transmittance at medium wave gradually decreases, but the transmittance at long wave and short wave gradually increases, and the transmission peak at long wave produces red shift, which makes the visible light transmission spectrum curve tend to be flat, so the high transmittance frequency domain gradually widens. At the same time, with the increase of the thickness of the top tantalum pentoxide, the average transmission of visible light first increases and then gradually decreases. In general, when the thickness of the top tantalum pentoxide is 30-50nm, the light transmission effect of the entire visible light band is better, and the equivalent admittance matching of the D'MD film structure composed of the Ag film with a thickness of 6-15nm is better, and the induced transmission effect is more significant. In addition, with the increase of the thickness of the top tantalum pentoxide film, the optical path difference of the interference effect of light in the film structure increases, causing the transmission peak to shift toward the long-wave direction.

[0098] Embodiment 3

[0099] Based on the basic structure of D'MD film, different materials, different thicknesses, different number of cycles, designs with different central wavelengths, different reflection bandwidths, and different protection effects can be used to achieve broadband protection or narrowband protection. The reflection bandwidth increases with the refractive index ratio n. H / n L That is to say, 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 1064nm has a structure of: D'MD.

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

[0101] The visible light infrared stealth and laser protection compatible film shown in this embodiment has a wider reflection bandwidth, with a 50% reflectivity bandwidth of 874.58-1252.6nm and a 90% reflectivity bandwidth of 885.24-1231.4nm, which can effectively address the problem of reflectivity drop at angle incidence. At a certain angle (0-40°) of incidence, the reflectivity is above 90%, the average visible light transmittance is above 70%, and the average infrared emissivity is below 9%. The thickness of each layer of the film system is given in Table 2.

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

[0103] Example Layer1 Layer2 Layer3 Layer4 Layer5 Layer6 3 115.30 189.27 115.30 189.27 115.30 189.27 Layer7 Layer8 Layer9 Layer10 Layer11 Layer12 Layer13 115.30 189.27 115.30 189.27 115.30 189.27 115.30 Layer14 Layer15 Layer16 Layer17 Layer18 Layer19 189.27 115.30 189.27 115.30 9 30

[0104] Embodiment 4

[0105] The structure of a symmetrical visible light infrared stealth and laser protection compatible film is: D / M / D' / M / D. The total number of layers of the laser protection film is 19, where D represents H, which is a high refractive index material zirconium dioxide (ZrO2), M represents a metal material gold (Au), D' represents (HL)^7H, and L represents a low refractive index material magnesium fluoride (MgF2). The physical thickness of each layer of the film system is given in Table 3.

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

[0107] Example Layer1 Layer2 Layer3 Layer4 Layer5 Layer6 4 31 10 130.71 192.71 130.71 192.71 Layer7 Layer8 Layer9 Layer10 Layer11 Layer12 Layer13 130.71 192.71 130.71 192.71 130.71 192.71 130.71 Layer14 Layer15 Layer16 Layer17 Layer18 Layer19 192.71 130.71 192.71 130.71 10 31

[0108] The camouflage film compatible with visible light infrared dual-band stealth and laser protection is designed to have a symmetrical structure, and has the same spectral characteristics and electric field distribution characteristics for incident light from the front or back of the film system. Therefore, the dual-band compatible camouflage film can be prepared into a micro-element reflector, and then prepared into a dual-band compatible camouflage coating material, which can be applied to the surface of drones, tanks, airplanes, satellites or other facilities that need to be protected by spraying, scraping, brushing, etc.

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

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

[0111] Embodiment 5

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

[0113] The total number of layers of the laser protection film is 19, and the central 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 metal material gold (Au), D' represents (HL)^8H, and L represents the low refractive index material silicon dioxide (SiO2). (HL)^8H is a 17-layer reflective film stack, which constitutes a D'MD structure with silver and hafnium dioxide.

[0114] By adjusting the thickness of the top hafnium dioxide film (20-200nm) to control the reflection in the visible spectrum, the designed structure can show different colors, represented in the CIE 1931 chromaticity diagram as follows Fig. 9 As shown. At the same time, its reflectivity at 1030nm is always maintained above 97% at normal incidence, and the average emissivity in the infrared band of 3000-14000nm is always less than 9%. Changing the D thickness does not affect the laser protection and infrared stealth effects. The visible light transmittance of the film can always be maintained above 80%, and it will have a slight color, which is conducive to shielding unnecessary sunlight in the optical windows of aircraft windows and other equipment. Therefore, the D'MD film not only has excellent visible light transparency, but also has good eye-friendly properties under strong light irradiation, and also has the effects of infrared stealth and laser protection. The physical thickness of each layer is given in Table 4.

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

[0116] Example Layer1 Layer2 Layer3 Layer4 Layer5 Layer6 5 140.31 181.98 140.31 181.98 140.31 181.98 Layer7 Layer8 Layer9 Layer10 Layer11 Layer12 Layer13 140.31 181.98 140.31 181.98 140.31 181.98 140.31 Layer14 Layer15 Layer16 Layer17 Layer18 Layer19 181.98 140.31 181.98 140.31 10 20-200

[0117] Embodiment 6

[0118] Based on the basic structure of D'MD, different visible light reflectances are obtained by changing the metal thickness to achieve different colors. The structure is:

[0119] D' / M / D

[0120] The total number of layers of the laser protection film is 19, and the central wavelength of the selected reflection band is 1030nm. Here D represents H, which is a high refractive index material yttrium trioxide (Y2O3), M represents a metal material silver (Ag), D' represents a stacked medium (HL)^8H, L is a low refractive index material silicon dioxide (SiO2), (HL)^8H is a 17-layer reflective film stack, and it forms a D'MD structure with silver and yttrium trioxide. As the thickness of the Ag layer increases from 2nm to 15nm, the color changes from blue to khaki and then to transparent. This phenomenon can be attributed to the Volmer-Weber mode growth of the silver layer at a thin thickness, which leads to nanoparticle formation and cracks, resulting in local surface plasmon resonance and multiple scattering effects, resulting in color changes due to interaction with light. This effect is alleviated when the separated nanoparticles are interconnected and grow to form a dense film.

[0121] Surface plasmons (SPPs) can be excited at the interface between the dielectric and the metal, which can effectively concentrate the electric field. D'MD films can significantly compress the free space wavelength, thereby enhancing transmission. From the electric field distribution, it can be seen that the upper and lower surfaces of Ag support SPPs in an asymmetric manner, resulting in faster energy degradation in the horizontal direction. Therefore, when the photon energy is not suitable for exciting SPPs, the field concentration ability decreases, the surface electromagnetic field dissipates quickly, and the transparency performance deteriorates.

[0122] Therefore, the color change of the film is mainly attributed to the plasma resonance absorption caused by the island growth of the ultra-thin silver layer, resulting in low infrared absorption and increased transmission, rather than just thickness. The visible light transmittance of the film can always be maintained above 90%, and it will have a slight color, which is beneficial for shielding unnecessary sunlight in the optical windows of aircraft windows and other equipment. Therefore, the D'MD film not only has excellent visible light transparency, but also has good eye-friendly properties under strong light irradiation, and also has the effects of infrared stealth and laser protection. The physical thickness of each layer is given in Table 5.

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

[0124] Example Layer1 Layer2 Layer3 Layer4 Layer5 Layer6 4 149.46 181.98 149.46 181.98 149.46 181.98 Layer7 Layer8 Layer9 Layer10 Layer11 Layer12 Layer13 149.46 181.98 149.46 181.98 149.46 181.98 149.46 Layer14 Layer15 Layer16 Layer17 Layer18 Layer19 181.98 149.46 181.98 149.46 2-20 40

[0125] The above descriptions are only some embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent device or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A laser thin film structure, characterized in that: The 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 second dielectric layer structure expression is H(LH)^s, wherein 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. A laser thin film structure according to claim 1, characterized in that: The refractive index of the high refractive index medium material is 1.6-4.0; The refractive index of the low-refractive-index dielectric material is 1.0-1.

6.

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

4. A laser thin film structure according to claim 1, characterized in that: The material of the metal layer includes: one or more of 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 second dielectric layer structure expression is H(LH)^s, wherein 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. A laser thin film structure as claimed in claim 5, characterized in that: The refractive index of the high refractive index medium material is 1.6-4.0; The refractive index of the low-refractive-index dielectric material is 1.0-1.

6.

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

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

9. A method for preparing a laser thin film structure, characterized in that: The method is used to prepare the thin film structure as claimed in any one of claims 1 to 8; Select high refractive index materials, low refractive index materials and metal layer materials; determine the number of film system periods according to the number of periods in which the reflectivity of the film to the central wavelength in the reflection band is greater than or equal to 99% and the difficulty of preparing the film; prepare the film by deposition method based on the above-determined parameters.

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

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