DE102018116993B4 - Optical component with scratch-resistant anti-reflection coating and method for its manufacture - Google Patents

Abstract

Optical component (10) with a substrate (1), provided with a layer stack (2) with several successive layers of different materials and different refractive indices, which forms an anti-reflective coating, wherein the optical component (10) is at least partially transparent in the infrared and visible spectral range , wherein the layers of the layer stack (2) are formed from at least three different materials or combinations of materials, so that the layer stack contains at least one layer of a first, second and third type with at least three different refractive indices, with a layer of the first type (4) having a higher refractive index as a second type layer (3) and a third type layer (5) has a lower refractive index than a second type layer (3), and wherein a top layer (7) and a second top layer are provided, the top layer ( 7) a second type ply (3) and the second top ply a first T ply yps (4) and thus has a refractive index which is higher than the refractive index of the top layer (7) and wherein the layer stack (2) has at least one further layer which is arranged in the layer stack (2) below the two top layers and is a layer of the third type (5) and thus has a refractive index which is lower than the refractive indices of the top two layers.

Description

field of invention

The invention relates generally to an anti-reflective coated optical component, and more particularly to an anti-reflective coated optical component having a substrate and to a method of coating the optical component and use thereof.

Background of the Invention

Antireflection coatings are often used today to improve the transmission of transparent substrates, such as viewing panes, or to reduce disruptive reflections on the substrate. However, depending on the intended use of the substrate, the anti-reflective coating can be subjected to high levels of wear and tear. For example, sand and dust particles hit the outer coating of a vehicle visor at high speed while driving and can wear away the coating over time. A particular stress also arises with such panes when a windshield wiper is run over the dirty pane. The sand and dust particles are not only transported over the windshield, but are also pressed against the windshield by the rubber lip of the windshield wiper. This can cause long scratches in the coating.

Scratches and other damage lead to turbidity due to light scattering, reduce the anti-reflection effect of the coating by changing it and therefore counteract the purpose of an anti-reflection coating.

There is therefore a need for an anti-reflective coating with high resistance to scratching and abrasion.

Abrasion or the formation of scratches typically occurs when an abrasive medium, e.g. B. a grain of sand, caused by lateral movement over the surface or by normal impact cracks in the material, some of which are only nanometric in size. The cracks usually only become visible and optically relevant when additional breakouts occur along the crack edges that scatter light, or even layer detachments occur. The behavior of a surface to form cracks depends on a large number of parameters, such as e.g. E.g. modulus of elasticity, surface roughness, brittleness, surface tension or the tendency of the two materials involved (substrate and abrasive medium) to form covalent bonds. The hardness of the substrate, e.g. B. as measured with an indenter method (e.g. Knoop hardness), is just one of many influencing parameters, albeit one of the most important.

From the U.S. 2005/0074591 A1 a transparent substrate with an abrasion-resistant anti-reflection coating is known. The anti-reflective coating is composed of four layers of alternating high and low refractive index. The low-index layers consist of silicon oxide (SiO ₂ ), the high-index layers of silicon nitride (Si ₃ N ₄ ) or tin oxide (SnO ₂ ). The top layer of the layer stack is formed from a low-index layer. The disadvantage here is that the low-index silicon oxide layer is very soft compared to the high-index materials, in particular compared to Si ₃ N ₄ . The top layer in particular can therefore still wear out quickly. Once the top layer has been removed, a highly refractive layer forms the surface. In the worst case, this leads to a reversal of the anti-reflective effect, so that the layer now acts more like a dielectric (half) mirror at the scratched area.

Furthermore, the CN 101782216A a reflector with a protective coating that consists of three layers and is anti-reflective in different ranges of the visible part of the electromagnetic spectrum. The three layers have different refractive indices. From the surface of the substrate underlying the protective layer to the air, the magnitude of the refractive indices are in the order of high - low - medium. The material of the layers is dielectric.

• - im sichtbaren Wellenlängen-Bereich zwischen ca. 450 nm und ca. 650 nm,
• - bei einer Laserwellenlänge im nahen Infrarotbereich zwischen 1000 nm und 1600 nm, beispielsweise bei den Laserwellenlängen von 1053nm, 1064 nm, 1535 nm oder 1550 nm,
• - im mittleren Infrarotbereich zwischen 3500 nm und 5000 nm, sowie
• - im fernen Infrarotbereich zwischen 7500 nm und 12000 nm

stehen nur wenige Materialien als Substrat für die optische Komponente zur Verfügung.Optical applications exist in various infrared regions of the electromagnetic spectrum. Materials such as sapphire, germanium or silicon are usually used for use in a single spectral range. However, if an optical component is to be functional in several areas of the electromagnetic spectrum at the same time, for example

• - in the visible wavelength range between approx. 450 nm and approx. 650 nm,
• - at a laser wavelength in the near infrared range between 1000 nm and 1600 nm, for example at the laser wavelengths of 1053 nm, 1064 nm, 1535 nm or 1550 nm,
• - in the middle infrared range between 3500 nm and 5000 nm, as well as
• - in the far infrared range between 7500 nm and 12000 nm

only a few materials are available as a substrate for the optical component.

The transmission for a wavelength in the near infrared range between 1000 nm and 1600 nm can be required for a LIDAR or so-called "range finder" application. Range finder whose active laser medium z. B. from ytterbium and erbium doped phosphate glass, such as. B. LG940, LG950 or LG960 (manufactured by SCHOTT AG), emit at 1535 nm.

Examples of suitable materials for such applications are zinc sulfide and zinc selenide. Most materials used for applications in the infrared spectral range do not transmit in at least one or more of the four ranges mentioned above. Although sapphire can be used in the visible, near and middle infrared range, it no longer transmits above 6000 nm. Germanium or silicon, which transmit in the far infrared range, cannot be used as a window in the visible. The choice of substrate materials for use from the visible to the far-infrared range is severely limited, and thus also the availability of any refractive index of possible substrate materials.

However, such materials are often soft or have little abrasion resistance and are brittle and only have a refractive index in the medium to high range (1.7 to 2.5). The relatively high refractive index is associated with a high reflectivity of the surface of the substrate made of such a material. In such cases, therefore, an anti-reflective coating is required. Only a few materials are available for this purpose as well. Zinc sulfide (ZnS), hafnium oxide (HfO ₂ ), scandium oxide (SC ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ) , niobium oxide (Nb ₂ O ₅ ), titanium oxide (TO ₂ ) and cerium oxide (CeO ₂ ). Barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), lanthanum fluoride (LaF ₃ ), neodymium fluoride (NdF ₃ ), ytterbium fluoride (YbF ₃ ), magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), dysprosium fluoride (DyF ₃ ) and yttrium fluoride (YF ₃ ).

In particular, the low-index layer materials have the disadvantage that they are soft. With anti-reflective coatings, it is typically necessary to apply a low index layer on the very outside as the last layer. This is particularly necessary when the anti-reflection coating is complex, i.e. when it is highly anti-reflective (substrate materials with a high refractive index) or is to be effective in several spectral ranges. Therefore, a fluoride layer is often used as the top layer. In particular, however, the low-index layer materials have the disadvantage that they are soft and therefore not scratch-resistant. In optical designs, an attempt is typically made to compensate for a lack of scratch resistance, at least to a small extent, by making the last layer very thick or by making the optical effectiveness of the coating less dependent on the thickness of the top layer.

The reduced scratch resistance of the soft top layer is disadvantageous when the respective optical component is used outdoors, for example as a sensor window in military vehicles and aircraft. When used in desert areas, for example, the disadvantage of the lack of scratch resistance increases due to the high sand content in the air. Fluoride layers made from the compounds listed above are therefore unsuitable for such conditions of use. Due to their water solubility, some of the oxides listed above are also not suitable for such uses.

In order to protect surfaces of optical elements from scratching, it is known to provide the surface with a hard coating. From the EP 2492251 A1 a hard anti-reflective coating is known.

In general, high refractive index infrared materials, e.g. B. germanium, with an extremely hard DLC layer (diamond-like carbon) are anti-reflective, since the refractive index of the substrate is significantly higher than that of the layer. In order to anti-reflection on a substrate surface with a single layer against air as the adjacent medium, as is the case in some applications with DLC, e.g. B. on germanium or with a fluoride layer (e.g. MgF ₂ ) on some glasses, the refractive index of the layer should ideally be close to the square root of the refractive index of the substrate. In the case of materials having a refractive index in the range of ZnS or ZnSe and below, but for multiple spectral ranges including the visible, DLC is unsuitable.

Brief description of the invention

The invention has for its object to provide an optical component for use in multiple spectral ranges with an anti-reflection coating compared to the Coatings according to the prior art has improved abrasion resistance.

This object is solved by the subject matter of the independent claims. Advantageous developments and embodiments of the invention are defined in the dependent claims.

The optical component according to the invention comprises a substrate provided with a layer stack with several successive layers of different materials and different refractive indices, which forms an anti-reflective coating, the optical component (10) being at least partially transparent in the infrared and visible spectral range, the layers of the layer stack consisting of at least three different materials or material combinations are formed, so that the layer stack contains at least one layer of a first, second and third type with at least three different refractive indices, a first-type layer having a higher refractive index than a second-type layer and a third-type layer having a lower refractive index as a second type layer, and wherein a top layer and a second top layer are provided, the top layer being a second type layer and the second top layer being a first type layer and thus a Has a refractive index which is higher than the refractive index of the top layer, and wherein the layer stack has at least one further layer which is arranged in the layer stack below the two top layers and is a layer of the third type and thus has a refractive index which is lower than the refractive indices of the top two layers.

In a preferred embodiment of the invention, the top layer, or the layer of the second type, is an oxide layer. This is advantageous because certain oxides, such as those listed below, exhibit a combination of high abrasion resistance and moderate to high refractive index.

Furthermore, the layer with the highest refractive index can consist of the same material as the substrate, e.g. B. from ZnS. This can e.g. B. can be an advantage when it comes to using a different layer material for the first layer, which shows good adhesion properties on the substrate and as a consequence can potentially be combined very well with the corresponding layer material.

• - im Bereich von 450 nm bis 650 nm,
• - bei einer oder mehreren Wellenlängen im Bereich von 1000 nm bis 1600 nm,
• - im Bereich von 3500 nm bis 5000 nm,
• - im Bereich von 7500 nm bis 12000 nm.

In order to be able to be used in several wavelength ranges of the electromagnetic spectrum, the substrate and the layer stack are at least partially transparent in the infrared and visible spectral range. In particular, the wavelength range from 450 nm to 650 nm comes into consideration as the visible spectral range. According to one embodiment of the invention, the interference layer system can now be designed in such a way that the substrate and the layer stack are at least partially transparent in at least one, preferably several, in particular all of the following wavelength ranges:

• - in the range from 450 nm to 650 nm,
• - at one or more wavelengths in the range from 1000 nm to 1600 nm,
• - in the range from 3500 nm to 5000 nm,
• - in the range from 7500 nm to 12000 nm.

Typically, more than three layers of the layer stack are useful for good antireflection properties, even in several wavelength ranges. In this case it is preferred to design the layer stack as an alternating layer system with layers of the first and third type alternating with one another and to provide a layer of the second type as the top layer. Finally, a layer of the second type is deposited, so that, as provided according to the invention, the second-top layer is a layer of the first type with a high refractive index. The second-top layer can be a layer of the third type if its layer thickness is preferably less than 300 nm, more preferably less than 100 nm and most preferably less than 20 nm. Alternatively, additional layers of the third type can be replaced by a layer of the second type, so that the replaced layer of the second type is enclosed on both sides by a layer of the first type. This can be advantageous since the material of the second type according to the invention is harder than the material of the third type and the scratch resistance depends not only on the properties of a surface but also on the stability of underlying materials and layers that support the layer at the surface. The reverse phenomenon is also commonly known as the so-called "chocolate kiss effect," where an inherently relatively hard surface (chocolate) can collapse into underlying, softer material (sugar foam). In order to counteract this effect, in which the top two layers of the second and first type collapse into the third-top layer of the third material, it is advantageous if not only the top layer consists of a material of the second type, but also the third- top and possibly also the fifth top. For the sake of simplicity, the layers made of materials of the second type are even made of the same material and such a layer system can be deposited with only three materials.

In general, it is advantageous if the stack of layers has a plurality of layers of the first type and a plurality of layers of the third type (each at least two layers) and only a single layer of the second type, which closes the stack of layers or forms the top layer of the stack of layers.

In a further preferred embodiment of the invention, the substrate of the optical component consists of zinc sulphide. This substrate also satisfies the characteristic of being transparent at the wavelengths specified above.

If the layer of the second type and thus the top layer is an oxide layer, it preferably contains a material that is taken from the group consisting of hafnium oxide (HfO ₂ ), scandium oxide (SC ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ), aluminum oxide (Al ₂ O ₃ ), and cerium oxide (CeO ₂ ) and mixed oxides of these oxides. The reason for this selection is that the listed materials or mixtures have medium to high refractive index. The refractive index of these materials ranges from 1.7 to 2.2.

Furthermore, an embodiment of the optical component is preferred in which the further layer is a fluoride layer. Due to the refractive indices of the fluorides used, this also further improves the anti-reflection behavior of the coating of the optical component. Furthermore, many fluorides are transparent in large parts of the wavelength ranges listed.

In this case, the further layer contains a fluoride taken from the group consisting of barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), lanthanum fluoride (LaF ₃ ), neodymium fluoride (NdF ₃ ), ytterbium fluoride ( YbF ₃ ), magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), dysprosium fluoride (DyF ₃ ) and yttrium fluoride (YF ₃ ). The refractive indices of these materials range from 1.3 to 1.9.

The second top layer contains a material which has a higher refractive index than the material taken from the group of chalcogenides, in particular the group of oxides, sulfides or selenides (which together with the tellurides are called chalcogenides) and in the corresponding wavelength ranges is transparent, e.g. B. the sulfide ZnS. The second-top layer can be a layer of the third type if its layer thickness is preferably less than 300 nm, more preferably less than 100 nm and most preferably less than 20 nm.

Furthermore, an embodiment of the coating is possible in which a material is selected for the first layer which exhibits particularly good adhesion properties or at least better adhesion properties with the substrate than the material of the third type. The main purpose of this layer is to promote adhesion between the substrate and the coating. The layer thus fulfills a chemical-mechanical and not an optical purpose. For this purpose, the thickness of this first layer can be only a few nanometers. For example, the layer thickness for this can be between 1 nm and 15 nm. On the other hand, in some applications with corresponding transmission requirements, it is also possible to use layer materials which transmit less well in the relevant wavelength ranges than the materials of the first, second and third types mentioned. As such an adhesion promoter z. B. aluminum oxide (Al ₂ O ₃ ) is known.

In a special embodiment of this version with improved layer adhesion, the adhesion-promoting layer consists of a material of the second type, e.g. B. HfO ₂ . Since in this case the material can be used as an optical layer material due to its transparency properties, the thickness of the adhesion promoter layer can again be so large that it fulfills a task as a component of the optical design.

Various methods can be used to coat the optical component according to the invention. In particular, the top layer can be deposited by a method taken from the group consisting of ion plating, ion implantation, ion assist/advanced plasma, magnetron sputtering, ion beam sputtering, cathodic arc deposition and atomic layer deposition. Especially the ion or plasma support is advantageous to increase the density, hardness and compressive stress of the top layer and thus make it more resistant to abrasion.

The top layer of the coating of the optical component according to the invention can also be deposited using a different method than the other layers of the layer stack. It is also possible, if more than one layer consists of the material of the last layer, for the last layer to be deposited using one method and the other or further layers of the same material using a different method. This is particularly advantageous when using a method to increase the density, hardness or compressive stress of the top layer which is not compatible with another layer material.

In a particular embodiment of the invention, the layer stack with the exception of the top most layer, which itself consists of two or more materials, is deposited by means of classic electron beam evaporation and an ion or plasma process is additionally switched on for the last layer, e.g. B. Ion Plating, Ion Assist or Advanced Plasma.

It can be advantageous to start depositing the top layer first without the additional ion or plasma process in order to protect the underlying material of the second top layer from the ion or plasma process with the first nanometers of material. This splits the top layer into two sub-layers of the same material, which have a similar refractive index, but not the same. Typically, the part that has been additionally deposited with the ion or plasma process has a slightly higher refractive index than the part that has been deposited without the additional process.

In a further embodiment, this protective layer, which protects the former second-top layer from the ion or plasma process, can consist of a further material. The layer fulfills a mechanical or radiation-related purpose and not an optical purpose. For this purpose, the thickness of this first layer can be only a few nanometers. On the other hand, in some applications with corresponding transmission requirements, it is also possible to use layer materials which transmit less well in the relevant wavelength ranges than the materials of the first, second and third types mentioned. For such a protective layer z. B. aluminum oxide (Al ₂ O ₃ ) but also use the materials of the third type.

The layer stack can have such an alternating layer sequence that there is at least one further layer with the same material as one of the three uppermost layers.

The bottom layer 9 can be a layer of the third layer type 5 with the lowest refractive index.

According to one embodiment, the stack of layers has a total of between seven and thirty layers, with four layers of the type of the further layer alternating with those of the type of the second top layer, or four layers of the first type with four layers of the second type. In addition, there is the top layer as the final layer, which at the same time closes off the stack of layers from the environment. It has been found that the anti-reflection properties are particularly good in this configuration.

According to the invention, the optical component is used in the single or multispectral visible and infrared range of the electromagnetic spectrum.

In the following, the invention will be described in more detail with reference to the accompanying drawings, in which the same reference numbers designate the same elements.

In a further embodiment, so-called needles are inserted in at least one layer, which is typically comparatively thick. Needles are layers with a thickness of a few nanometers, preferably from 2 nm to approx. 50 nm. The lower limit of the layer thickness of the needles is usually limited by the coating technology. With electron beam vapor deposition, layers with a thickness of less than 5 - 10 nm are usually not closed or too heterogeneous to be used for the application, depending on the layer material. Some CVD processes, such as B. ALD (Atomic Layer Deposition), however, allows usable layers of z. B. 2 or 3 nm.

Needles bring various benefits. For example, they interrupt B. crystal growth and limit grain boundaries. The layers are statistically more amorphous and show fewer defects and less light scattering. Another advantage is that layer stress can be reduced and compensated. The substrate shows less coating-induced warping (Reflected Wavefront Distortion) and the risk of delamination either at the interface to the substrate or between coating layers is reduced. It is often even optically advantageous and the spectral performance of a coating can be increased without significantly increasing the overall thickness of the coating layer stack. This is advantageous for the duration of the coating and thus for the costs of the coating. Needles are well known to those skilled in the art of optical coating design. They are particularly useful in the inventive coatings of this disclosure since relatively thick layers must be used due to the fact that the coating is to be optically transparent over a very large range of wavelengths up to the far infrared.

An example of a coating with needles according to the invention is the following: Zinc sulfide (ZnS) with a refractive index of 2.24, yttrium fluoride (YF ₃ ) with a refractive index of 1.47, and hafnium oxide are used as layer materials for a coating on a zinc sulfide substrate (HfO ₂ ) with a refractive index of 2.01, all used at 1000 nm wavelength. The coating is carried out by means of electron beam evaporation. The top layer is made of hafnium oxide The process is divided into two: The first 10 nanometers are deposited using normal electron beam evaporation - the rest of the layer using APS (Advanced Plasma Source). The layer thicknesses are as follows: substrate (ZnS), (1.) 10 nm HfO ₂ , (2.) 25 nm YF ₃ , (3.) 25 nm ZnS, (4.) 225.8 nm YF ₃ , (5 .) 10 nm ZnS, (6.) 250 nm YF ₃ , (7.) 10 nm ZnS, (8.) 250 nm YF ₃ , (9.) 10 nm ZnS, (10.) 250 nm YF ₃ , ( 11.) 10 nm ZnS, (12.) 150 nm YF ₃ , (13.) 10 nm ZnS, (14.) 50 nm YF ₃ , (15.) 60 nm ZnS, (16.) 65 nm HfO ₂ , Air. This example is an anti-reflective coating for the visible spectral range and the far infrared from 8 to 11 microns. Such a structure can be interpreted in two ways: (1) thick layers of one material alternate with thin layers of another material. Or (2) a very thick low-index part is interrupted by very thin high-index needles: A thick low-index part of 225.8 nm + 250 nm + 250 nm + 250 nm + 150 nm +50 nm = 1175.8 nm YF ₃ is broken by 5 needles interrupted, each consisting of 10 nm ZnS. For the light, in particular the long-wave radiation in the far infrared range (FIR), the optical path length and thus the phase change within the needle is negligible. The interaction with the matter is mainly determined by the reflectivity at the two interfaces. The embodiment with the needles thus generally represents, without being restricted to the above example, an alternating layer system as part of the coating, in which layers of two types alternate, the layers of one type being thicker than the layers of the other type. This alternating layer system preferably comprises at least a total of four consecutive layers. Preferably, the layers of one type are consistently at least a factor of ten thicker than the layers of the other type. In particular, the thin layers can continue to be those of the first type (ie with a high refractive index) and the thick layers can be those of the third type (ie with a low refractive index). Corresponding to the above thickness specification for the needles, the thinner layers also preferably have a layer thickness in the range from 2 nm to 50 nm.

In a coating according to the invention, any number of areas with a thickness of 100 nm or more can be interrupted by needles: next to none at all, between one and all. Any region of material 100 nm or more thick may be interrupted by one or more needles, besides none at all. Different areas with a thickness of 100 nm or more can be interrupted by different numbers of needles. Both areas of a material with a thickness of 100 nm or more can be interrupted by needles of another or several other materials, and areas of different materials with a thickness of 100 nm can be interrupted by needles of another or several other materials. Some or all of the needles may be made of a third material, which differs from the two materials that mainly make up the layer system as high and low refractive index layers. If you release a coating design for optimization in optimization software that either already contains needles, or if you release a coating design that already contains needles for optimization in the optimization software, it may be possible that an optimized design contains needles , which not only make it mechanically advantageous, but that the design also has a higher quality spectrally and optically than a comparable optimized design without needles.

In a particular embodiment, it is advantageous to protect layers that have already been deposited by needling a third material before the deposition process of the subsequent layer with a relevant optical thickness. This is e.g. B. the case when supporting plasma processes of a layer to be deposited damaged an already deposited layer and z. B. breaks covalent bonds or releases atoms of a species from which the underlying layer consists, and the material at the surface in a stoichiometrically unfavorable composition changes, so that these z. B. shows a higher absorption. In this case, it is advantageous to deposit a needle only on a layer of material that is sensitive to the deposition process of the other material. In another case, however, it can also be possible that two materials could be used together for a design that is optically advantageous, but the two materials are not compatible with each other for other reasons. Examples of incompatibilities are e.g. B. lack of layer adhesion or the chemical change of a layer material in that one of its atomic species reacts with a species from the other material at the interface to another optically unfavorable material. Such a reaction can either happen immediately during the coating process, during a subsequent tempering process (thermal annealing) or later as a result of an accelerated or additional aging or degradation process. In the example given above, a needle was deposited directly as the first layer on the substrate to serve as an adhesion promoter between the substrate and the rest of the coating. In particular, it makes sense to use a needle to protect the penultimate "thick" layer from a plasma process, which can be used for the last layer to make it and thus the entire coating particularly abrasion-resistant.

In a further embodiment, so-called nanolaminates can be used as individual layers. Publications that describe "nanolaminates", i.e. very thin layers in a thickness range of 2 to 10 nm, for example, are J. Meyer, et al.: "Al ₂ O ₃ /ZrO ₂ Nanolaminates as Ultrahigh Gas-Diffusion Barriers - A Strategy for Reliable Encapsulation of Organic Electronics”, in: Advanced Mater. 2009, 21 1845-1849, Wiley-VCH Verlag Weinheim, 2009 or J. Meyer: "The origin of low water vapor transmission rates through Al ₂ O ₃ /ZrO ₂ nanolaminate gas-diffusion barriers grown by atomic layer deposition", in: Applied Physics Letters 96, 243308 (2010), American Institute of Physics, 2010.

Nanolaminates are layers that are made up of a large number of very thin layers, which usually consist of two alternating materials. For example, a nanolaminate layer can be constructed from Al ₂ O ₃ and HfO ₂ or from Al ₂ O ₃ and Ta ₂ O ₅ . Of course, it is also possible to construct such nanolaminates from more than just two materials. The individual layers are usually a few nanometers thick. Such a nanolaminate acts optically like a thick layer that has an average refractive index and can thus be integrated into an interference multilayer coating with further thicker layers of one or more other materials. Such nanolaminates are usually used because of their advantageous mechanical properties. A nanolaminate could be interpreted as a stack of layers made up exclusively of needles.
Nanolaminates get their properties from the large number of interfaces and very thin layers, where bulk properties are sometimes negligible. Parameters that significantly influence the properties of nanolaminates and that do not exist for monolithic layers are e.g. B. the so-called "duty cycle", ie the ratio of the layer thicknesses of the individual needles to each other. Typical examples are 3 nm Al ₂ O ₃ and Ta ₂ O ₅ each or alternating 3 nm Al ₂ O ₃ and 10 nm Ta ₂ O ₅ . Such layer thicknesses cannot be produced homogeneously with classic electron beam vapor deposition processes. But there are other methods, such as B. Atomic Layer Deposition (ALD) used in the cited publications. It is even possible to build up layers other than the coating using ALD. In the examples given, ZnS and YF ₃ are used. Both materials can also be deposited using ALD: JRBakke, et.al.: "Atomic layer deposition of ZnS via in situ production of H ₂ S", in Thin Solid Films, Volume 518, Issue 19, 2010, 5400-5408 and Tero Pilvi, et al.: "ALD of YF3 Thin Films from TiF4 and Y(thd)3 Precursors" in Chemical Vapor Deposition, Volume15, Issue1-3, 2009, 27-32.

In a coating according to the invention, one or more of the layers can be constructed as a nanolaminate. Both high-index layers and low-index layers as well as medium-index layers can be nanolaminates. In particular, it can be advantageous to construct the last layer as a nanolaminate consisting of an oxide and a fluoride. This combines the advantage of the relatively greater hardness of the oxide compared to the fluoride with the advantage that such a nanolaminate has a lower average optically relevant refractive index compared to the hard oxide. It is for the optical quality of a coating design, which should exhibit low reflectivity, if the final layer has an index of refraction that is as low as possible. It is also possible to optimize the duty cycle in such a way that the nanolaminate consists of more fluoride than oxide and the refractive index is therefore lower than that of a nanolaminate that consists of 50% fluoride and 50% oxide. but at the same time has a significantly greater hardness or abrasion resistance than a pure fluoride.

In general, without being restricted to specific examples, it is therefore provided according to one embodiment of the invention that at least one of the layers of the coating is a nanolaminate made up of a large number of layers with thicknesses between 2 nm and 10 nm and these layers consist of at least two alternating materials .

According to further embodiments, as stated, the top layer of the coating represents such a nanolaminate. As explained above, this can in particular comprise an alternating layer system of fluoride and oxide layers.

Furthermore, from the disclosures CH 709 524 A2 ("Hard anti-reflective coatings and their production and use") and DE 10 2016 125 689 A1 (“Substrate comprising anti-reflection coating system with hard material coating and method for its production”) that a higher abrasion resistance of a multi-layer coating can also be achieved if the top layer is not changed, but the layers underneath are significantly harder or more stable be made. This phenomenon can now also be applied to the coating according to the invention, in that a layer which lies below the top layer, designed as a nanolaminate, has a greater hardness. For example, the last layer, which includes ZnS, can be constructed together with an oxide as a nanolaminate and thus by supporting the give the final low-index layer greater stability.

character list

• 1 eine schematische Darstellung des erfindungsgemäßen Schichtstapels der optischen Komponente,
• 2 ein Diagramm der Transmission einer 4-Band Anti-Reflexionsbeschichtung auf einem 4 mm dicken Substrat aus ZnS.
• 3 eine schematische Darstellung des erfindungsgemäßen Schichtstapels der optischen Komponente aus 1, versehen mit einer zusätzlichen Haftvermittlerschicht,
• 4 eine schematische Darstellung des erfindungsgemäßen Schichtstapels der optischen Komponente aus 1, wobei die oberste Schicht in zwei Unterschichten aufgeteilt ist,
• 5 eine schematische Darstellung des erfindungsgemäßen Schichtstapels der optischen Komponente aus 1, versehen mit einer zusätzlichen Schutzschicht,
• 6 schematische Darstellung des erfindungsgemäßen Schichtstapels der optischen Komponente aus 1, versehen mit Nadeln, beziehungsweise dünnen Zwischenschichten, und
• 7 eine schematische Darstellung des erfindungsgemäßen Schichtstapels der optischen Komponente aus 1, versehen mit einem Nanolaminat.

In the drawings is

• 1 a schematic representation of the layer stack of the optical component according to the invention,
• 2 a diagram of the transmission of a 4-band anti-reflection coating on a 4 mm thick ZnS substrate.
• 3 a schematic representation of the layer stack according to the invention of the optical component 1 , provided with an additional adhesion promoter layer,
• 4 a schematic representation of the layer stack according to the invention of the optical component 1 , where the top layer is divided into two sublayers,
• 5 a schematic representation of the layer stack according to the invention of the optical component 1 , provided with an additional protective layer,
• 6 schematic representation of the layer stack according to the invention of the optical component 1 , provided with needles or thin intermediate layers, and
• 7 a schematic representation of the layer stack according to the invention of the optical component 1 , provided with a nanolaminate.

Without being restricted to the layer structure shown, shows 1 a schematic representation of the layer sequence of the layer stack 2 of an optical component 10 as a section, the layer stack 2 serving as an anti-reflection coating.

An optical component 10 with an anti-reflection coating according to the invention is produced using a method in which a substrate 1 is provided with a layer stack 2 with a plurality of successive layers of different materials and different refractive indices, which forms an anti-reflection coating, the layers of the layer stack 2 consisting of at least three different materials or combinations of materials are deposited successively, so that the layer stack produced by the successive deposition contains at least one layer of a first, second and third type with at least three different refractive indices, with a first-type layer having a higher refractive index than a second-type layer and a third type layer has a lower refractive index than a second type layer, and wherein a top layer and a second top layer are provided, the top layer 7 being a second type layer 3 and the second top layer ei ne layer of the first type 4 and thus has a refractive index which is higher than the refractive index of the top layer, and wherein the layer stack 2 has at least one further layer which is arranged in the layer stack 2 under the two top layers and a layer of the third type 5 and thus has a refractive index which is lower than the refractive indices of the two uppermost layers.

The substrate 1 of the example shown is provided with a layer stack 2, which here consists of a total of nine consecutive layers of different materials and different refractive indices. The layers of the layer stack 2 are formed from at least three different materials or combinations of materials, so that the layer stack has at least one layer of a first, second and third type. The types of layers differ with regard to their refractive index, so that the layer stack contains layers with at least three different refractive indices. A first-type layer 4 has a higher refractive index than a second-type layer 3 and a third-type layer 5 has a lower refractive index than a second-type layer 3 . The top layer 7 of the layer stack 2 is in contact with the environment and is therefore exposed to environmental influences and should therefore consist of a material that is as abrasion-resistant as possible.

The top layer 7 is a layer of the second type 3 and the second top layer is a layer of the first type 4 and thus has a refractive index which is even higher than the refractive index of the top layer 7. The layer stack 2 has at least one further layer which is arranged in the layer stack 2 under the two uppermost layers and is a layer of the third type 5 and therefore has a refractive index which is lower than the refractive indices of the two uppermost layers of the first and second type 4,3. Below the sequence of the top layer 7, the second top layer 4 and the further layer 5, layers alternate which consist of the same material as the second top layer 4 and the further layer 5.

in the in 1 In the exemplary embodiment shown, four layers of the second-top layer 4 and the further layer 5 alternate below the top layer 7, so that the layer stack shown has a total of nine layers, taking into account the top layer 7, which corresponds to a preferred embodiment of the anti-reflection coating since the anti-reflection behavior is particularly good in this configuration. the alternating layers of the first and third types 4, 5 form an alternating layer system. The stack of layers is then completed with a single ply of the second type as the top layer. Since the refractive index of the top layer is lower than the refractive index of the second top layer, an antireflection effect is achieved on the one hand and high mechanical resistance on the other hand, despite the higher refractive indices compared to layers of the first type.

In particular, the substrate 1 can consist of zinc sulfide. In one embodiment, the second-top layer 4 consists of the same material as the substrate 1, ie in particular zinc sulfide, ZnS.

One of the following oxides is particularly suitable as the material for the uppermost layer 7 or for the layer of the second type: hafnium oxide (HfO ₂ ), scandium oxide (SC ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ) , niobium oxide (Nb ₂ O ₅ ), yttria (Y ₂ O ₃ ), titanium oxide (TiO ₂ ), alumina (Al ₂ O ₃ ) and cerium oxide (CeO ₂ ). The reason for this selection is the combination of refractive indices and hardness of these materials. An increased hardness of the top layer 7 is also produced in that the top layer 7 is applied particularly hard using special techniques. The following methods can be used for this: ion plating, ion implantation, ion assist/advanced plasma, magnetron sputtering, ion beam sputtering, cathodic arc deposition and atomic layer deposition. It is not necessary to use the same method for applying all the layers of the layer stack 2 . Different methods can also be combined with one another. For example, according to one embodiment, all layers apart from the top layer 7 can be thermally vapor-deposited, while the top layer 7 is applied by means of a sputtering process. Changing the coating process is still economical if you only have to change the top layer.

One of the following fluorides is particularly suitable as the material for the one or more layers of the third type 5: barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), lanthanum fluoride (LaF ₃ ), neodymium fluoride (NdF ₃ ), ytterbium fluoride (YbF ₃ ), magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), dysprosium fluoride (DyF ₃ ) and yttrium fluoride (YF ₃ ). The material of the layer of the third type 5 is selected in such a way that the refractive index of the individual layers increases from the further layer 5 via the second-top layer 4 to the top layer 7 .

The overall arrangement of substrate 1 and layer stack 2 is in the infrared and visible spectral range at wavelengths from 450 nm to 650 nm, at one or more wavelengths between 1000 nm and 1600 nm, at wavelengths between 3500 nm to 5000 nm and in the far infrared at wavelengths from 8 µm to 12 µm at least partially transparent, so that it can be used, for example, as a window for cameras that are sensitive in the wavelength ranges mentioned.

The invention is particularly suitable for infrared optics, including lens systems. Such infrared optics can then be combined with several sensors that are sensitive in the visible and infrared spectral range. Examples of this are so-called range finders or thermal cameras. A preferred application is use as a cover window for an infrared camera, for example in an airplane, tank, automobile or drone.

In 2 the transmission of an anti-reflection coating, which is at least partially transparent for four frequency ranges, of a 4 mm thick substrate 1 made of ZnS is plotted against the wavelength, with a logarithmic scaling being chosen for the wavelength. The diagram of 2 shows the course of the transmission as a percentage of the incident radiation.

The course of transmission of an uncoated substrate is represented by graph 22 . This increases with increasing wavelength at a wavelength of about 380 nm almost vertically to 65% and at a wavelength of about 1000 nm it changes to a horizontal section at 74%.

The transmission of a substrate coated on both sides according to the invention, represented by the line 21, follows a transmission specification in four sections 21a, 21b, 21c, 21d. In the section 21a, between 420 nm and 720 nm, the visible wavelength range, the transmission is everywhere about 20% above the graph 22 for an uncoated substrate. At 1530-1550 nm, the wavelength of so-called "eye-safe" LIDARS or range finders, the transmission curve has another section 21b, which shows a peak of well over 90% at that wavelength and thus also around 20% over the transmission of the uncoated substrate. The transmission of a substrate coated according to the invention has a further section of high transmission. This increases steeply at a wavelength of approx. 3000 nm. At a wavelength of approx. 13,000 nm, the transmission falls off sharply. Typically, two wavelength ranges are used in this region of technical applications, on the one hand the range 21c from 3500 nm to 5000 nm for the detection of objects with a high temperature, such as e.g. B. Jet engines or combustion engines, on the other hand, the area 21d from 7500 nm to 11500 nm for body temperature detection. In these two areas, too, the transmission profile 21 of the coated substrate shows a transmission that is approximately 20% higher than the line 22 of the uncoated substrate.

The coating is therefore a 4-band anti-reflection coating. This is transparent and anti-reflective for wavelengths in the visible spectral range, for a so-called "eye safe" range finder, as well as for thermal radiation from engines and living bodies.

The example of a coating according to the invention consists of the three layer materials YF ₃ , ZnS and HfO ₂ . In the example shown, the three layer materials have the following refractive indices: material coating technology Refractive index at 1000 nm YF ₃ E beam 1.49 ZnS E beam 2.28 HfO ₂ E beam 1.90 HfO ₂ ion plating 2.11

The last two layers in this example each consist of HfO ₂ . However, the first half is deposited using a standard electron beam vapor deposition process (e-beam). The second half is deposited using ion plating. In this way, the last non-oxidic layer is protected by the first HfO ₂ partial layer from the ion plating process, which would damage the underlying non-oxidic layer and impair its transmission or absorption within the meaning of the invention. The layer structure is as follows: substrate, 20.1 nm YF ₃ , 36.1 nm ZnS, 60.3 nm YF ₃ , 25.8 nm ZnS, 42.7 nm YF ₃ , 243.6 nm ZnS, 168 .5 nm YF ₃ , 89.2 nm ZnS, 170.2 nm YF ₃ , 46.1 nm ZnS, 35.6 nm HfO ₂ (e-beam), 35.6 nm HfO ₂ (ion plating), air. The result for a double-sided coating with this design on a 10 mm thick ZnS substrate is the measured transmission spectrum 21.

3 1 shows an embodiment in which an additional adhesion promoter layer 6 is applied to the substrate 1 in order to increase the adhesion of the layer stack 2 to the substrate 1. This adhesion promoter layer 6 is generally characterized in that its adhesion to the substrate 1 is better than the adhesion of a layer 4 of the third type. According to a first development of the invention, the adhesion promoter layer 6 can be kept so thin that optically it has little or no effect on the reflection properties of the layer stack. In this case, the layer thickness is preferably at least 1 nm and/or preferably less than 10 nm. In general, with a thin layer, a material can also be used which has a higher absorption coefficient in the visible and/or infrared spectral range than the materials of the layers first, second and third type. This is because, due to the small layer thickness, the overall transmission is not significantly reduced because of the small layer thickness. A suitable material for the adhesion promoter layer, which provides high adhesion to many substrate materials, is aluminum oxide, Al ₂ O ₃ .

According to another embodiment of the invention, the adhesion promoter layer 6 can also simultaneously be an optically active component of the layer stack 2, which contributes to the anti-reflection effect. For this purpose, the adhesion promoter layer 6 can in particular be a layer of the second type.

In the embodiment according to 4 the top layer 7 is divided into a first sub-layer 11 and a second sub-layer 12 , with the second sub-layer 12 forming the surface of the layer stack 2 . The first sub-layer 11 is applied without a supporting ion or plasma process; such a supporting process is used during the deposition of the second sub-layer 12 . In this way it is avoided that the high-energy ions during the ion-assisted deposition chemically or physically damage the underlying layer 4 of the first type. In contrast, the ion support leads to a dense layer structure of the second sub-layer 12. The two sub-layers 11, 12 are thus made of the same material, but differ in terms of their density. Typically, the density of the second sub-layer 12 and hence its refractive index is greater. The ion support leads to a dense and resistant surface.

In the embodiment according to 5 an additional protective layer 13 is applied below or in front of the top layer 7 in order to protect the material of the layer 4 from the ion or plasma process during the deposition of the top layer 7 . Accordingly, it is generally provided in this embodiment that the protective layer is deposited in front of the uppermost layer 7 and the uppermost layer 7 is deposited on the protective layer and in contact with it. In the embodiment according to 6 the optical component 10 has an alternating layer system in which layers 4 made of material of the third type alternate with layers 5 made of material of the first type. The thickness of the layers 4 is greater than the thickness of the layers 5 by at least a factor of 10. The latter Layers in the form of very thin intermediate layers are also referred to as "needles".

In the embodiment according to 7 one of the two layers 5 is designed as a so-called nanolaminate 50 . This layer comprises several consecutive thin layers with thicknesses between 2 nm and 10 nm.

The coating according to the invention was subjected to two standard tests in order to check its scratch or abrasion resistance. The first standard test was the so-called Bayer test according to ASTM F735-11, TABER. Quartz sand is used as the abrasive medium, which has the following properties: grading 5/9 roundness: 0.6+ sphericity 0.6+ hardness 7.0 SG 2.65 loss on ignition 0.1 MP 2800°/3100° colour brown/white PH value 6.9-7.0

The typical chemical composition of the quartz sand used in weight percent is as follows: SiO ₂ 99.48% by weight _{Fe2O3 _} 0.06% by weight _{Al2O3 _} 0.21% by weight MgO <0.01% by weight

Such quartz sand can be purchased commercially from Rimer Silica, Texas, USA.

Another relevant test for such applications and coatings is the so-called wiper test, sometimes also called the washability test, according to the TS1888 standard.

The coated sample is mounted in a holder and the outer, coated surface is added for 5 minutes at 1000 wipe cycles per hour (2000 strokes per hour) with a standard car windshield wiper blade at a wiper load of 20 grams per cm a mixture of sand and water (1 cm ³ sand according to DEF STAN 07-55 type C, in 10 milliliters of water).

At the end of the test, the sample must show no visible signs of scratching when visually inspected.

The layer thickness of a standard coating with a fluoride as the top, final layer was reduced by an average (macroscopically) 70 nm in this test, while the reduction in the thickness of the coating according to the invention was on average (macroscopically) only 12 nm. Both coatings had the same spectral specification. To analyze these reduced layer thicknesses, reverse engineering was carried out with regard to the optical layer design of the reflection spectra measured before and after abrasion.

The so-called windshield wiper test with dirty water in accordance with the TS 1888 standard (windshield wiper test) was used as a further standard test for checking the abrasion resistance. The windscreen wiper exerts a pressure of 22 N and performs 100 movements per minute over an angular range of 60 degrees. The percent haze change is measured at appropriate intervals according to the ASTM D 1003 standard. Once the average haze of the mid-range reaches 5%, it is generally considered to be at the end of its useful life.

Other options for checking abrasion resistance are a modified Bayer test with corundum sand and sand and dust abrasion according to MIL-STD-810G method %10.5. An eraser abrasion test according to DIN ISO 9211-4-01-03 can also be used.

• - Menge der Oberflächendefekte nach ISO10110,
• - Größe der Oberflächendefekte nach ISO10110,
• - Lichtstreuung, gemessen auf Basis des Hazewertes,
• - Reflexion in einem definierten Wellenlängenbereich,
• - Transmission in einem definierten Wellenlängenbereich, oder
• - Schärfe des durch die Komponente transmittierten Bildes (Distinctness of Image (DOI)).

The abrasion resistance is measured in such a way that at least one of the following parameters is measured before and after carrying out at least one of the test methods described:

• - Amount of surface defects according to ISO10110,
• - size of surface defects according to ISO10110,
• - light scattering, measured on the basis of the haze value,
• - Reflection in a defined wavelength range,
• - Transmission in a defined wavelength range, or
• - Sharpness of the image transmitted through the component (Distinctness of Image (DOI)).

Comparing an optical component according to the invention with a component with the The same substrate material and a coating that is comparable in terms of optical behavior, but in which the top layer consists of a fluoride, there is a significant improvement in the abrasion resistance of a component according to the invention. Compared to an optical component as described above with an uppermost fluoride layer, it has been shown that with a component according to the invention there is also a deterioration in the above-mentioned parameters (amount of surface defects according to ISO10110, their size, etc.), but this by at least 20%. is reduced compared to the optical component with the top fluoride layer.

Reference List

1

substrate

2

layer stack

3

position of the second type

4

position of the third type

5

location of the first type

6

Additional adhesion promoter layer

7

top layer

9

lowest position

10

Optical component

11

Second sub-class of 7

12

First subclass of 7

13

Additional layer of protection

21a,b,c,d

Transmission curve with anti-reflection coating

22

Transmission curve without anti-reflection coating

50

nanolaminate

Claims (26)

Optical component (10) with a substrate (1), provided with a layer stack (2) with several successive layers of different materials and different refractive indices, which forms an anti-reflective coating, wherein the optical component (10) is at least partially transparent in the infrared and visible spectral range , wherein the layers of the layer stack (2) are formed from at least three different materials or combinations of materials, so that the layer stack contains at least one layer of a first, second and third type with at least three different refractive indices, with a layer of the first type (4) having a higher refractive index as a second type layer (3) and a third type layer (5) has a lower refractive index than a second type layer (3), and wherein a top layer (7) and a second top layer are provided, the top layer ( 7) a second type layer (3) and the second top layer a first T layer yps (4) and thus has a refractive index which is higher than the refractive index of the top layer (7) and wherein the layer stack (2) has at least one further layer which is arranged in the layer stack (2) below the two top layers and is a layer of the third type (5) and thus has a refractive index which is lower than the refractive indices of the top two layers. Optical component according to the preceding claim, wherein a low-index layer with a thickness between 2 nm and 50 nm is inserted under the top layer. An optical component (10) according to any one of the preceding claims, wherein the top layer is an oxide layer. An optical component (10) according to any one of the preceding claims, wherein the layer (4) with the highest refractive index consists of the same material as the substrate (1). Optical component (10) according to one of the preceding claims, wherein the layer stack (2) is designed as an alternating layer system of layers of the first and third type alternating with one another and a layer of the second type is provided as the top layer. Optical component (10) according to one of the preceding claims, wherein the layer stack (2) comprises a plurality of layers of the first type and a plurality of layers of the third type (4, 5) and a single layer of the second type (3) which is the top layer of the layer stack (2) forms. Optical component according to one of the preceding claims, in which the layer stack (2) comprises an adhesion-promoting layer (6) which has better adhesion to the substrate (1) than a layer of the third type. Optical component after claim 6 , wherein the adhesion promoter layer (6) contains a material which is taken from the group comprising aluminum oxide and hafnium oxide, or which is a layer of the second type. An optical component as claimed in any preceding claim, wherein the top layer (7) comprises a first sub-layer (12) and a second sub-layer (11) of the same material but of different refractive index. Optical component according to one of the preceding claims, in which a protective layer (13) is deposited in front of the top layer (7) and the top layer (7) is deposited on and in contact with the protective layer (13), the protective layer (13) being a layer is of the third type and its layer thickness is less than 300 nm. Optical component according to one of the preceding claims, wherein the layer stack comprises an alternating layer system in which layers of two types alternate, the layers of one type being thicker than the layers of the other type, wherein at least one of the following features applies: - the alternating shift system comprises at least four consecutive shifts, - the layers of one type are at least ten times thicker than the layers of the other type, - the thin layers are layers of the first type and the thick layers are layers of the third type, - the thin layers have a thickness between 2 nm and 50 nm. Optical component according to one of the preceding claims, wherein at least one of the layers of the layer stack (2) forms a nanolaminate from a multiplicity of layers with thicknesses between 2 nm and 10 nm and these layers consist of at least two alternating materials. Optical component according to one of the preceding claims, characterized in that the substrate and the layer stack are at least partially transparent in at least one of the following wavelength ranges: - in the wavelength range from 400 nm to 650 nm, - one or more wavelengths in the range from 1000 nm to 1600 nm, - in the wavelength range from 3500 nm to 5000 nm, - in the wavelength range from 7500 nm to 12000 nm. An optical component (10) according to any one of the preceding claims, wherein the substrate (1) is made of zinc sulphide or zinc selenide. Optical component (10) according to one of the preceding claims, in which the layer of the second type (3) contains a material taken from the group consisting of hafnium oxide (HfO ₂ ), scandium oxide (SC ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantala (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), yttria (Y ₂ O ₃ ), titania (TiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), and mixtures thereof. An optical component (10) according to any one of the preceding claims, wherein the further layer (5) is a fluoride layer. Optical component (10) according to the preceding claim, wherein the further layer (5) contains a fluoride taken from the group consisting of barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), lanthanum fluoride (LaF ₃ ), neodymium fluoride (NdF ₃ ), ytterbium fluoride (YbF ₃ ), magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), dysprosium fluoride (DyF ₃ ), yttrium fluoride (YF ₃ ), and mixtures thereof. Optical component (10) according to one of the preceding claims, in which the top layer (3) is applied by means of a different method than the other layers of the layer stack (2). Optical component (10) according to one of the preceding claims, wherein the layer stack (2) has such an alternating layer sequence that at least one further layer is present with the same material as one of the three uppermost layers. An optical component (10) according to any one of the preceding claims, wherein the bottom layer (9) is a layer of the third layer type with the lowest refractive index. Optical component (10) according to one of the preceding claims, wherein the layer stack (2) has a total of between seven and thirty layers. Optical component (10) according to any one of the preceding claims, wherein the optical component shows no visible signs of scratches on the surface after a slide wiper test according to standard TS1888 and the amount of surface defects according to ISO10110 compared to an optical component with a fluoride top layer by at least 20% reduced. Method for producing an optical component (10) with an anti-reflective coating, the optical component being at least partially transparent in the infrared and visible spectral range, in which a substrate (1) with a layer stack (2) with a plurality of successive layers of different materials and different refractive indices, which forms an anti-reflection coating, the layers of the layer stack (2) consisting of at least three different materials or combinations of materials being deposited successively, so that the layer stack produced by the successive deposition has at least one layer of a first, second and third type with at least three under contains different refractive indices, a first-type layer having a higher refractive index than a second-type layer and a third-type layer having a lower refractive index than a second-type layer, and wherein a top layer and a second top layer are provided, the top layer (7th ) is a layer of the second type (3) and the second-top layer is a layer of the first type (4) and thus has a refractive index which is higher than the refractive index of the top layer, and wherein the layer stack (2) has at least one further layer which is arranged in the layer stack (2) below the two top layers and is a layer of the third type (5) and thus has a refractive index which is lower than the refractive indices of the two top layers. Method according to the preceding claim, in which the layer of the second type (3) is applied using one of the following methods: ion plating, ion implantation, ion assist/advanced plasma, magnetron sputtering, ion beam sputtering, cathodic arc deposition and atomic layer deposition. Method according to the preceding claim, characterized in that the layer of the second type is applied in the form of two sub-layers (11, 12), the second sub-layer (11) being applied without a supporting plasma or ion process and the first sub-layer (12) with a supporting plasma or ion process. Use of the optical component (10) according to one of Claims 1 until 22 in the single or multispectral visible and infrared regions of the electromagnetic spectrum.

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