IL267969B2

IL267969B2 - Optical component with scratch-resistant anti-reflection coating and method for producing same

Info

Publication number: IL267969B2
Application number: IL267969A
Authority: IL
Original assignee: Schott Ag
Priority date: 2018-07-13
Filing date: 2019-07-10
Publication date: 2025-02-01
Also published as: AU2019205016A1; FR3083739B1; DE102018116993A1; AU2019205016B2; FR3083739A1; IL267969B1; GB201909990D0; GB2575554A; IL267969A; GB2575554B; DE102018116993B4

Description

17SGL0242ILPSCHOTT AGP 4713IL OPTICAL COMPONENT WITH SCRATCH-RESISTANT ANTI-REFLECTION COATING AND METHOD FOR PRODUCING SAME Field of the Invention The invention generally relates to an optical component provided with an anti-reflection coating, and more particularly to an optical component provided with an anti-reflection coating with a substrate, and to a method for coating the optical component, and to the use thereof.

Background of the Invention Anti-reflection coatings are widely used nowadays to improve the transmission of transparent substrates such as viewing windows, and on the other hand to mitigate disturbing reflections on the substrate. However, depending on the intended use of the substrate, the anti-reflection coating may be subject to high wear loads. For example, an exterior coating of a vehicle's windshield will be subjected to sand and dust particles that impact at high speed during driving, which may wear off the coating over time. A special load moreover arises for such windshields when a windshield wiper is passed over the dirty windshield. The sand and dust particles are not only conveyed over the windshield, but are at the same time pressed against the windshield by the rubber lip of the windshield wiper. This may cause long scratches in the coating.

Scratches and other damage lead to haze due to light scattering, reduce the antireflective effect of the coating by altering it, and thus counteract the purpose of an anti-reflection coating.

Therefore, there is a need for an anti-reflection coating that exhibits a high resistance against scratching and abrasion.

Abrasion or the formation of scratches is typically caused by an abrasive medium, such as a grain of sand, causing cracks of partly only nanometer-scale size in the material by laterally moving over the surface or by normal impact. The cracks mostly not become visible and visually relevant before additional break-outs occur along the edges of the cracks, which scatter light, or before even delamination occurs. The behavior of a surface to form cracks depends on a variety of 17SGL0242ILPSCHOTT AGP 4713IL parameters such as Young's modulus, surface roughness, brittleness, near-surface stress, or the tendency of the two involved materials (substrate and abrasive medium) to form covalent bonds. The hardness of the substrate, as measured using an indenter test method (e.g. Knoop hardness) is only one of many influencing parameters, albeit one of the most important ones.

From US 2005/0074591 A1, a transparent substrate with an abrasion-resistant anti-reflection coating is known. The anti-reflection coating is composed of four layers of alternating high and low refractive indices. The low refractive index layers consist of silicon oxide (SiO2), the high refractive index layers consist of silicon nitride (Si3N4) or tin oxide (SnO2). The uppermost layer of the layer stack is formed by a low refractive index layer. A drawback hereof is that the low refractive index silicon oxide layer is very soft compared to the high-index materials, in particular when compared with Si3N4. Therefore, it is especially the uppermost layer that still can wear out quickly. When the uppermost layer has been worn off, then a high-index layer forms the surface. In the worst case this results in a reversal of the anti-reflection effect, so that the layer is then rather effective as a dielectric (half) mirror at the scratch point.

There are optical applications in different infrared ranges of the electromagnetic spectrum. For use in a single spectral range, materials such as sapphire, germanium, or silicon are commonly employed. However, if an optical component is intended to be functional in several ranges of the electromagnetic spectrum at the same time, for example- in the visible wavelength range between about 400 nm and about 650 nm, preferably between about 450 nm and about 650 nm,- at a laser wavelength in the near infrared range between 1000 nm and 1600 nm, e.g. at the laser wavelengths of 1053 nm, 1064 nm, 1535 nm, or 1550 nm,- in the mid-infrared range between 3500 nm and 5000 nm, and- in the far infrared range between 7500 nm and 12000 nm,there are only a few materials available as a substrate material for the optical component.

Transmission for a wavelength in the near infrared range between 1000 nm and 1600 nm might be needed for a LIDAR application, also known as range finder application. Range finders which include ytterbium- and erbium-doped phosphate glass as an active laser medium, e.g. LG940, LG950, or LG960 (manufactured by SCHOTT AG), emit at 1535 nm. 17SGL0242ILPSCHOTT AGP 4713IL Examples of suitable materials for such applications are zinc sulfide and zinc selenide. Most of the materials that are used for applications in the infrared spectral range do not transmit in at least one or more of the four ranges listed above. Although sapphire can be used in the visible, near and mid-infrared range, it is no longer transmissive above 6000 nm. Germanium or silicon, which are transmissive in the far infrared range, cannot be used as a window in the visible range. The choice of substrate materials for use from the visible up to the far infrared range is very limited, and so is the availability of any desired refractive indices of possible substrate materials.

However, such materials are often soft or little abrasion resistant and brittle and only have a refractive index in the medium to high range (1.7 to 2.5).The rather high refractive index is associated with a high reflectivity of the surface made of such a material. Therefore, an antireflection coating is needed in such cases. There are also only a few materials available for this purpose. High-index layer materials that come into consideration for the anti-reflection coating include, for example, zinc sulfide (ZnS), hafnium oxide (HfO2), scandium oxide (Sc2O3), yttrium oxide (Y2O3), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), titanium oxide (TiO2), and cerium oxide (CeO2). Low-index layer materials that come into consideration for the anti-reflection coating include, for example, barium fluoride (BaF2), calcium fluoride (CaF2), cerium fluoride (CeF3), lanthanum fluoride (LaF3), neodymium fluoride (NdF3), ytterbium fluoride (YbF3), magnesium fluoride (MgF2), aluminum fluoride (AlF3), dysprosium fluoride (DyF3), and yttrium fluoride (YF3).

A drawback in particular of the low refractive index layer materials is that they are soft. For antireflection coatings it is typically necessary to apply a low refractive index layer as the last, outermost layer. This is in particular necessary if the anti-reflection coating is complex, i.e. if it has a strong anti-reflection effect (high refractive index substrate materials) or if it shall be effective in a plurality of spectral ranges. Therefore, a fluoride layer is often used as the uppermost layer. However, in particular the low refractive index layer materials have the disadvantage that they are soft and therefore not scratch-resistant. In optical designs, it is typically attempted to compensate for the lack of scratch resistance at least in part by a very large layer thickness of the last layer or by a reduced dependence of the optical efficiency of the coating on the layer thickness of the uppermost layer. 17SGL0242ILPSCHOTT AGP 4713IL The reduced scratch resistance of the soft uppermost 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 drawback of lacking scratch resistance is exacerbated due to the high sand content in the air. Therefore, fluoride layers of the compounds listed above are unsuitable for such operating conditions. Some of the oxides listed above are unsuitable as well for such uses, due to their water solubility.

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

Generally, high refractive index infrared materials, such as germanium, can be anti-reflection coated with an extremely hard diamond-like carbon (DLC) layer, since the refractive index of the substrate is significantly higher than that of the layer. For providing an anti-reflective effect for a substrate surface with a single layer vis-a-vis air as an adjacent medium, as is done in some applications using DLC, for example on germanium, or using a fluoride layer (e.g. MgF2) on some glasses, the refractive index of the layer should ideally be close to the square root of the refractive index of the substrate. However, in the case of materials that have a refractive index in the range of that of ZnS or ZnSe and below, DLC is unsuitable for multiple spectral ranges including the visible.

Brief Description of the Invention The present invention is based on the object to provide an optical component with an antireflection coating that is suitable for use in multiple spectral ranges and that features improved abrasion resistance over the prior art coatings.

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

The optical component according to the invention comprises a substrate provided with a layer stack that includes a plurality of successive layers of different materials and different refractive 17SGL0242ILPSCHOTT AGP 4713IL indices, which defines an anti-reflection coating, wherein the layers of the layer stack are made from at least three different materials or material combinations, so that the layer stack contains at least one layer of each of a first type, second type, and third type, with at least three different refractive indices, wherein a layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than a layer of the second type; and wherein an uppermost layer and a second uppermost layer are provided, wherein the uppermost layer is a layer of the second type and the second uppermost layer is a layer of the first type and thus has a refractive index which is higher than the refractive index of the uppermost layer; and wherein the layer stack includes at least one further layer which is disposed below the two uppermost layers within the layer stack and which is a layer of the third type and thus has a refractive index which is lower than the refractive indices of the two uppermost layers.

In a preferred embodiment of the invention, the uppermost layer or layer of the second type is an oxide layer. This is advantageous because certain oxides such as those listed below combine high abrasion resistance with a medium to high refractive index.

Furthermore, the layer with the highest refractive index can be made of the same material as the substrate, for example of ZnS. This may be an advantage when it comes to use another layer material for the first layer, which has good adhesion properties on the substrate and, as a consequence, can potentially be combined very well with the respective layer material.

In order to be usable for a plurality of 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 is considered as the visible spectral range. According to one embodiment of the invention, the interference layer system can now be designed such that the substrate and the layer stack are at least partially transparent in at least one, preferably in a plurality of and in particular in 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. 17SGL0242ILPSCHOTT AGP 4713IL Typically, more than three layers of the layer stack are useful for having good anti-reflection properties in a plurality of wavelength ranges. In this case, it is preferred to form the layer stack as an alternating layer system with alternating layers of the first and third types and to provide a layer of the second type as the uppermost layer. A layer of the second type is deposited finally, so that the second uppermost layer is a layer of the first type with a high refractive index, as contemplated according to the invention. The second uppermost layer may be a layer of the third type if it has a layer thickness of preferably less than 300 nm, more preferably less than 100 nm, and most preferably less than 20 nm. Alternatively, layers of the third type may additionally be replaced by a layer of the second type such that the replacing layer of the second type is enclosed on both sides by a respective layer of the first type. This may be advantageous since the material of the second type is harder than the material of the third type according to the invention, and since the scratch resistance depends not only on the properties of a surface but also on the stability of underlying materials and layers supporting the surface layer. The reverse phenomenon is more commonly known as the "chocolate-coated marshmallow" effect, where an inherently relatively hard surface (chocolate) can break down into underlying softer material (sugar foam). In order to counteract this effect, where the top two layers of the second and first types break into the third uppermost layer of the third material, it is therefore advantageous if not only the uppermost layer is made of a material of the second type, but also the third uppermost layer and optionally also the fifth uppermost layer. 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 using only three materials.

Generally, it will be advantageous in this case if the layer stack comprises a plurality of layers of the first type and a plurality of layers of the third type (at least two layers in each case) and only a single layer of the second type, which closes the layer stack and forms the uppermost layer of the layer stack.

In a further preferred embodiment of the invention, the substrate of the optical component consists of zinc sulfide. This substrate also meets the feature of being transparent at the wavelengths given above. 17SGL0242ILPSCHOTT AGP 4713IL If the layer of the second type and thus the uppermost layer is an oxide layer, it preferably comprises a material selected from the group comprising hafnium oxide (HfO2), scandium oxide (Sc2O3), yttrium oxide (Y2O3), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), titanium oxide (TiO2), aluminum oxide (Al2O3), and cerium oxide (CeO2), and mixed oxides of these oxides. The reason for this selection is that the listed materials or mixtures have a 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, the anti-reflection behavior of the coating of the optical component is further improved. Furthermore, many fluorides are transparent in large parts of the stated wavelength ranges.

In this case, the further layer comprises a fluoride selected from the group comprising barium fluoride (BaF2), calcium fluoride (CaF2), cerium fluoride (CeF3), lanthanum fluoride (LaF3), neodymium fluoride (NdF3), ytterbium fluoride (YbF3), magnesium fluoride (MgF2), aluminum fluoride (AlF3), dysprosium fluoride (DyF3), and yttrium fluoride (YF3). These materials have refractive indices in the range from 1.3 to 1.9.

The second uppermost layer comprises a material which has a higher refractive index than the material of the uppermost layer and may be selected from the group of chalcogenides, in particular from the group of oxides, sulfides or selenides (which together with the tellurides are referred to as chalcogenides) and which is transparent in the respective wavelength ranges, such as the sulfide ZnS. The second uppermost layer may be a layer of the third type if it has a layer thickness of 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 adhesive properties or at least better adhesive properties to the substrate than the material of the third type. The main purpose of this layer is promoting adhesion between the substrate and the coating. Thus, the layer fulfills a chemical-mechanical and not an optical purpose. For this purpose, this first layer may have a thickness of only a few nanometers. For example, the layer thickness may be between 1 nm and 15 nm. So, in some 17SGL0242ILPSCHOTT AGP 4713IL applications with respective transmission requirements, it is even possible to use layer materials which transmit less well in the relevant wavelength ranges than the aforementioned materials of the first, second, and third types. For example aluminum oxide (Al2O3) is known to be such an adhesion promoter.

In a specific embodiment of this version with improved layer adhesion, the adhesion promoting layer consists of a material of the second type, e.g. HfO2. Since in this case the material can be utilized as an optical layer material, due to its transparency properties, the thickness of the adhesion promoting layer can in turn be large enough to fulfil a task as part of the optical design.

There are various techniques that can be used for coating the optical component according to the invention. The uppermost layer may in particular be applied by a process that is selected from the group comprising 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 assist is advantageous in order to increase the density, hardness and compressive stress of the uppermost layer so as to make it more resistant to abrasion.

Also, the uppermost layer of the coating of the optical component according to the invention may be deposited by a different process than the other layers of the layer stack. If more than one layer is made of the material of the last layer, it is even possible to deposit the last layer by one process and the other or further layers made of the same material by a different process. This is particularly advantageous if a process that is used to increase the density, hardness or compressive stress of the uppermost layer, is incompatible with another layer material.

In a particular embodiment of the invention, the layer stack, with the exception of the uppermost layer, which itself consists of two or more materials, is deposited by conventional electron beam evaporation, and for the last layer an ion or plasma process such as ion plating, ion assist or advanced plasma is additionally activated.

It may be advantageous to initially begin the deposition of the uppermost layer without the additional ion or plasma process, in order to protect, with the first nanometers of material, the material of the underlying second uppermost layer from the ion or plasma process. As a result, 17SGL0242ILPSCHOTT AGP 4713IL the uppermost layer will be subdivided into two sublayers of the same material, which have a similar refractive index, but not the same. Typically, the portion deposited by additionally using the ion or plasma process will have a slightly higher refractive index than the portion that was deposited without the additional process.

In a further embodiment, this protective layer which protects the formerly second uppermost layer from the ion or plasma process, may be made of a further material. The layer fulfills a mechanical or radiation-technical, but no optical purpose. For this purpose, the thickness of this first layer may comprise only a few nanometers. So, in some applications with respective transmission requirements it is even possible to use layer materials which transmit less well in the relevant wavelength ranges than the aforementioned materials of the first, second, and third types. For example aluminum oxide (Al2O3) can be used for such a protective layer, but also the materials of the third type.

The layer stack may include an alternating layer sequence which comprises at least one further layer made of the same material as one of the three uppermost layers.

The lowermost layer 9 may be a layer of the third layer type 5 having the lowest refractive index.

According to one embodiment, the layer stack comprises a number of between seven and thirty layers in total, with four respective layers of the type of the further layer alternating with those of the type of the second uppermost layer, or four respective layers of the third type alternating with four layers of the first type. Additionally, the uppermost layer is added to this as a final layer which at the same time seals the layer stack to the environment. It has been found that with this embodiment, the anti-reflection properties are particularly good.

According to the invention, the optical component is used in a single spectral range or in multi- spectral visible and infrared ranges of the electromagnetic spectrum.

In a further embodiment, so-called needle layers are interposed in at least one layer that is typically comparatively thick. Needle layers are layers having a thickness of a few nanometers, preferably from 2 nm to about 50 nm. The lower limit of the layer thicknesses of the needle layers 17SGL0242ILPSCHOTT AGP 4713IL is usually limited by the coating technology. With electron beam vapor deposition, layers of a thickness of less than 5 to 10 nm will usually not be contiguous or will be too heterogeneous, depending on the layer material, to be used for the application. However, some CVD procedures, such as atomic layer deposition (ALD), allow for useful layers of, e.g., 2 or 3 nm.

Needle layers bring about several advantages. For example, they interrupt crystal growth and limit grain boundaries. The layers are statistically more amorphous and exhibit less defects and less light scattering. Another advantage is that layer stress can be reduced and compensated for. The substrate exhibits less coating-induced warp (reflected wavefront distortion), and the risk of layer delamination, either at the interface to the substrate or else between coating layers, is reduced. Often it is even visually advantageous, and the spectral performance of a coating can be increased without significantly increasing the total thickness of the layer stack of the coating. This is of advantage in terms of coating time and therefore coating costs. Needle layers have been known to those skilled in the art with respect to the design of optical coatings. They are particularly useful in the coatings of the present disclosure, since relatively thick layers must be used due to the fact that the coating is intended to be optically transparent over a very large wavelength range up to the far infrared.

An example of a coating according to the invention that includes needle layers is as follows: The coating materials used for a coating on a zinc sulfide substrate include zinc sulfide (ZnS) having a refractive index of 2.24, yttrium fluoride (YF3) having a refractive index of 1.47, and hafnium oxide (HfO2) having a refractive index of 2.01, at a wavelength of 1000 nm in each case. Coating is achieved by electron beam evaporation. The uppermost layer made of hafnium oxide is divided into two portions in terms of the coating process: The first 10 nanometers are deposited by normal electron beam evaporation - the rest of the layer is deposited using advanced plasma source (APS). The layer thicknesses are as follows: substrate (ZnS), (1st) 10 nm HfO2, (2nd)nm YF3, (3rd) 25 nm ZnS, (4th) 225.8 nm YF3, (5th) 10 nm ZnS, (6th) 250 nm YF3, (7th) 10 nm ZnS, (8th) 250 nm YF3, (9th) 10 nm ZnS, (10th) 250 nm YF3, (11th) 10 nm ZnS, (12th) 150 nm YF3,(13th) 10 nm ZnS, (14th) 50 nm YF3, (15th) 60 nm ZnS, (16th) 65 nm HfO2, air. This example represents an anti-reflection coating for the visible spectral range and for the far infrared from 8 to pm. 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 refractive index portion is interrupted 17SGL0242ILPSCHOTT AGP 4713IL by very thin high refractive index needle layers: A thick low refractive index portion comprising 225.8 nm + 250 nm + 250 nm + 250 nm + 150 nm + 50 nm = 1175.8 nm of YF3 is interrupted by needle layers consisting of 10 nm ZnS each. For the light, in particular the long-wave radiation in the far infrared range (FIR), the optical path length and hence the phase change within the needle layer is negligible. The interaction with matter is mainly determined by the reflectivity at the two interfaces. Thus, more generally and without being limited to the above example, the embodiment with the needle layers represents an alternating layer system as part of the coating, in which layers of two types alternate, wherein the layers of one type are thicker than the layers of the other type. This alternating layer system preferably comprises at least four successive layers in total. Preferably, the layers of the one type are consistently thicker by at least a factor of ten than the layers of the other type. Furthermore, the thin layers may in particular be of the first type (i.e. with high refractive index), and the thick layers may be of the third type (i.e. with low refractive index). Furthermore, in correspondence to the thicknesses of the needle layers as stated above, the thinner layers preferably have a layer thickness in the range from 2 nm to 50 nm.

A coating according to the invention may include any desired number of portions having a thickness of 100 nm or more that are interrupted by needle layers: no portion at all, or between one and all. Any portion of a material having a thickness of 100 nm or more may be interrupted by no needle layer at all, or by one or more than one. Different portions having a thickness of 100 nm may be interrupted by different numbers of needle layers. It is possible for portions made of one material and having a thickness of 100 nm or more to be interrupted by needle layers of one or more other materials, and also for portions made of different materials and having a thickness of 100 nm to be interrupted by needle layers of one or more other materials. Some or all of the needle layers may be made of a third material that is different from the two materials mainly making up the layer system as high and low refractive index layers. If either a coating design that already contains needle layers is released for optimization in an optimization software, or if the optimization software is given a coating design that already contains needle layers, for optimization, it may happen that an optimized design contains needle layers which do not only make it advantageous in terms of mechanics, but that the design moreover has a higher quality in terms of spectral or optical behavior than a comparable optimized design without needle layers. 17SGL0242ILPSCHOTT AGP 4713IL According to one particular embodiment it is advantageous to protect already deposited layers by needle layers made of a third material prior to the deposition process of the subsequent layer that has a relevant optical thickness. This is the case, for example, if assisting plasma processes for a layer to be deposited would damage an already deposited layer and would, for example, break covalent bonds or dissolve atoms of a species of which the underlying layer is made of and would alter the material at the surface so as to take an unfavorable composition in terms of stoichiometry, so that it would exhibit higher absorptance, for example. In this case it is advantageous to deposit a needle layer only on a layer of the material which is sensitive to the deposition process of the other material. Furthermore, in another case it may be possible that although two materials could be used together with optical advantages for a design, the two materials are not compatible with each other for other reasons. Examples of incompatibilities include, e.g., insufficient layer adhesion, or chemical alteration of a layer material caused by a reaction of one of its atomic species with a species of the other material at the interface so as to form a different, optically unfavorable material. Such a reaction may either happen immediately during the coating process, or during a subsequent annealing process (thermal annealing), or later, by an accelerated or additional aging or degradation process. In the above example, a needle layer was deposited directly on the substrate, as a first layer, to be effective as an adhesion promoter between the substrate and the rest of the coating. It makes in particular sense to protect, by a needle layer, the penultimate "thick" layer from a plasma process that can be employed for the last layer, in order to make it, and hence the entire coating, particularly resistant to abrasion.

In a further embodiment, so-called nanolaminates can be used as individual layers. References describing the 'nanolaminates', i.e. very thin layers in a thickness range of, e.g., 2 to 10 nm, include, inter alia, J. Meyer, et al.: "Al2O3/ZrO2 Nanolaminates as Ultrahigh Gas-Diffusion Barriers - A Strategy for Reliable Encapsulation of Organic Electronics", in: Advanced Mater. 2009, 1845-1849, Wiley-VCH publishing house Weinheim, 2009; or J. Meyer: "The origin of low water vapor transmission rates through Al2O3/ZrO2 nanolaminate gas-diffusion barriers grown by atomic layer deposition", in: Applied Physics Letters 96, 243308 (2010), American Institute of Physics, 2010. 17SGL0242ILPSCHOTT AGP 4713IL Nanolaminates are layers that are made up of a multitude of very thin layers usually consisting of two alternating materials. For example, a nanolaminate layer may be composed of Al2O3 and HfO2, or of Al2O3 and Ta2O5. It is of course possible to compose such nanolaminates from more than two materials. The individual layers usually have a thickness of a few nanometers. Such a nanolaminate is optically effective like a thick layer that has an average refractive index, and therefore it can be integrated into an interference multilayer coating with further thicker layers made of one or more other materials. Such nanolaminates are usually used because of advantageous mechanical properties. A nanolaminate could be interpreted as a layer package that is exclusively composed of needle layers.

Nanolaminates attain their property by the large number of interfaces and very thin layers in which bulk properties are partially negligible. Parameters that have a significant influence on the properties of nanolaminates and that do not exist for monolithic layers include, for example, the so-called "duty cycle", i.e. the ratio of the layer thicknesses of the individual needle layers to each other. Typical examples are 3 nm of each of Al2O3 and Ta2O5, or 3 nm of Al2O3 alternating with nm of Ta2O5. Such layer thicknesses cannot be produced homogeneously by conventional electron beam vapor deposition processes. However, there are other methods, such as atomic layer deposition (ALD), which is used in the cited publications. It is even possible to grow other layers of the coating by ALD. In the described examples, ZnS and YF3 are used. Both materials can also be deposited using ALD: J.R.Bakke, et.al.: "Atomic layer deposition of ZnS via in situ production of H2S", 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, Volume 15, Issue 1-3, 2009, 27-32.

In a coating according to the invention, one or more of the layers may now be composed as a nanolaminate. Nanolaminates may be high-index layers and low-index layers and also medium- index layers. It may in particular be advantageous to compose the last layer as a nanolaminate consisting of an oxide and a fluoride. This combines the advantage of the relatively higher 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. For the optical quality of a coating design that shall exhibit low reflectivity it is of advantage if the last layer has a refractive index that is as low as possible. In this respect it is furthermore possible to optimize the 17SGL0242ILPSCHOTT AGP 4713IL duty cycle such that the nanolaminate is composed of more fluoride than of oxide and so the refractive index is lower than in the case of a nanolaminate consisting of 50 % fluoride and 50 % oxide, but at the same time additionally has a significantly higher hardness or abrasion resistance than a pure fluoride.

More generally, without being limited to specific examples, it is therefore contemplated according to one embodiment of the invention that at least one of the layers of the coating is a nanolaminate made of a multitude of layers with thicknesses between 2 nm and 10 nm, and that these layers are made of at least two alternating materials.

According to further embodiments, the uppermost layer of the coating is such a nanolaminate, as mentioned before. In particular, it may comprise a alternating layer system of fluoride and oxide layers, as explained above.

Furthermore, it is known from patent application publications CH 709 524 A2 ("Harte Anti-Reflex- Beschichtungen sowie deren Herstellung und Verwendung", i.e. "Hard anti-reflection coatings and their preparation and use") and DE 10 2016 125 689.7 ("Substrat umfassend Anti-Reflex- Beschichtungssystem mit Hartstoffbeschichtung sowie Verfahren zu dessen Herstellung", i.e. "Substrate comprising anti-reflection coating system with hard coating and method for producing same") that a higher abrasion resistance of a multi-layer coating can also be achieved if, although the uppermost layer is not altered, underlying layers are made significantly harder or more stable. This phenomenon can now also be applied to the coating according to the invention, by forming a layer that is disposed below the uppermost layer as a nanolaminate so as to have a greater hardness. For example, the last layer that comprises ZnS may be composed as a nanolaminate, together with an oxide, and can thus provide greater stability by supporting the final low refractive index layer.

The invention will now be described in more detail with reference to the accompanying drawings in which the same reference numerals designate the same elements. 17SGL0242ILPSCHOTT AGP 4713IL Brief Description of the Drawings In the drawings:FIG. 1 is a schematic view of the layer stack of the optical component according to the invention;FIG. 2 is a diagram of transmittance of a 4-band anti-reflection coating on a ZnS substrate of mm thickness;FIG. 3 is a schematic view of the layer stack of the optical component according to the invention of FIG. 1, provided with an additional adhesion promoting layer;FIG. 4 is a schematic view of the layer stack of the optical component according to the invention of FIG. 1, in which the uppermost layer is divided into two sublayers;FIG. 5 is a schematic view of the layer stack of the optical component according to the invention of FIG. 1, provided with an additional protective layer;FIG. 6 is a schematic view of the layer stack of the optical component according to the invention of FIG. 1, provided with needle layers or thin intermediate layers; and FIG. 7 is a schematic view of the layer stack of the optical component according to the invention of Fig. 1, provided with a nanolaminate.

Without being limited to the illustrated layer structure, FIG. 1 shows a schematic sectional view of the sequence of layers of the layer stack 2 of an optical component 10, which layer stack serves as an anti-reflection coating.

An optical component 10 with anti-reflection coating according to the invention is produced by a method in which a substrate 1 is provided with a layer stack 2 including a plurality of successive layers of different materials and different refractive indices, which defines an anti-reflection coating, wherein the layers of the layer stack 2 are successively deposited from at least three different materials or material combinations such that the layer stack produced by the successive deposition contains at least one layer of each of a first type, second type, and third type, with at least three different refractive indices, wherein a layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than a layer of the second type; and wherein an uppermost layer and a second uppermost layer are provided, wherein the uppermost layer 7 is a layer of the second type 3 and the second 17SGL0242ILPSCHOTT AGP 4713IL uppermost layer is a layer of the first type 4 and thus has a refractive index which is higher than the refractive index of the uppermost layer; and wherein the layer stack 2 includes at least one further layer which is disposed below the two uppermost layers within the layer stack 2 and which is 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 illustrated example is provided with a layer stack 2 which, here, consists of a total of nine successive layers made of different materials and having different refractive indices. The layers of the layer stack 2 are formed from at least three different materials or material combinations, so that the layer stack has at least one layer of each of the first, second, and third types. The types of layers differ in their refractive indices, so that the layer stack contains layers with at least three different refractive indices. In this case, a layer of the first type has a higher refractive index than a layer of the second type 3, and a layer of the third type has a lower refractive index than a layer of the second type 3. The uppermost layer 7 of the layer stack 2 is in contact with the environment, so it is exposed to environmental influences and should therefore consist of a material which is the most abrasion-resistant possible.

The uppermost layer 7 is a layer of the second type 3, and the second uppermost layer is a layer of the first type 4 and therefore has a refractive index which is even higher than the refractive index of the uppermost layer 3. The layer stack 2 has at least one further layer which is disposed below the two uppermost layers in the layer stack 2 and which is a layer of the third type 5 and therefore has a refractive index that is lower than the refractive indices of the two uppermost layers of the first and second types 4, 3. Below the sequence consisting of the uppermost layer 3, the second uppermost layer 4, and the further layer 5, there are alternating layers consisting of the same material as the second uppermost layer 4 and the further layer 5.

In the exemplary embodiment shown in FIG. 1, there are four layers of each type of the second uppermost layer 4 and of the further layer 5 alternating with each other below the uppermost layer 3, so that the illustrated layer stack has nine layers in total when taking into account the uppermost layer 3, which corresponds to a preferred embodiment of the anti-reflection coating, since the anti-reflection behavior is particularly good in this constellation. The alternating layers of the first and third types 4, 5 form an alternating layer system. The layer stack is then completed 17SGL0242ILPSCHOTT AGP 4713IL with a single layer of the second type as the uppermost layer. Since the refractive index of the uppermost layer is lower than the refractive index of the second uppermost layer, an antireflection effect is achieved on the one hand, despite of the higher refractive indices compared to the layers of the third type, and on the other hand also high mechanical resistance.

The substrate 1 may in particular be made of zinc sulfide. In one embodiment, the second uppermost layer 4 is made of the same material as the substrate 1, i.e. in particular of zinc sulfide, ZnS.

In particular one of the following oxides is suitable as a material for the uppermost layer 3 or the layer of the second type: hafnium oxide (HfO2), scandium oxide (Sc2O3), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), yttrium oxide (Y2O3), titanium oxide (TiO2), aluminum oxide (Al2O3), and cerium oxide (CeO2). The reason for this selection is the combination of refractive indices and hardness of these substances. An increased hardness of the uppermost layer 3 is moreover created by applying the uppermost layer 3 with special techniques to make it particularly hard. The following techniques can be used for this purpose: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 technique for applying all layers of the layer stack 2. Different techniques can be combined with each other. For example, according to one embodiment, all layers except for the uppermost layer 3 can be deposited thermally by vapor deposition, while the uppermost layer 3 is applied by a sputter deposition process. A switch in the coating technique is still economical if it only has to be made for the top layer.

In particular one of the following fluorides is suitable as a material for the one or more layers of the third type 5: barium fluoride (BaF2), calcium fluoride (CaF2), cerium fluoride (CeF3), lanthanum fluoride (LaF3), neodymium fluoride (NdF3), ytterbium fluoride (YbF3), magnesium fluoride (MgF2), aluminum fluoride (AlF3), dysprosium fluoride (DyF3), and yttrium fluoride (YF3). The material of the layer of the third type 5 is selected such that the refractive index of the individual layers increases from the further layer 5 via the second uppermost layer 4 to the uppermost layer 3. 17SGL0242ILPSCHOTT AGP 4713IL According to one example, the topmost layer, being a layer of the 2nd type is a HfO2-layer. This layer is deposited onto a ZnS layer, being a layer of the 1st type. This layer is followed by a layer of the 3rd type or one or more optional other layers followed by the layer of the 3rd type, the layer of the 3rd type being a YF3-layer. This layer may be in contact to the substrate, or alternatively, one or more opional other layers may be interposed between the substrate and the layer of the 3rd type. This embodiment is particularly suited with a zinc selenide (ZnSe) substrate. However, a ZnS substrate is suited as well. Summarizing, the layer sequence according to this embodiment is:HfO2 (2nd type) / ZnS (1st type) / optional layers / YF3 (3rd type) / optional layers / ZnSe- substrate.

As an alternative to HfO2, the one or more layers of the second type may be layers of Sc2O3,ZrO2, Ta2O5, Nb2O5, Y2O3, TiO2, Al2O3, CeO2. Further, materials alternative to YF3 for the layer of the 3rd type are BaF2, CaF2, CeF2, LaF3, NdF3, YbF3, MgF2, AlF3, DyF3.

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

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

FIG. 2 shows a graph of transmittance plotted versus wavelength of an anti-reflection coating of a ZnS substrate 1 of 4 mm thickness that is at least partially transparent for four frequency ranges, wherein a logarithmic scale has been selected for the wavelength. The graph of FIG. 2 shows the profile of transmittance as a percentage of the incident radiation. 17SGL0242ILPSCHOTT AGP 4713IL The transmittance profile of a non-coated substrate is represented by curve 22, which, at a wavelength of about 380 nm, rises almost vertically with increasing wavelength up to 65 %, and at a wavelength of about 1000 nm, at 74 %, it turns into a horizontal section.

The transmittance of a substrate that is coated on both sides according to the invention is represented by curve 21 which follows a transmittance specification in four sections 21 a, 21 b, c, 21 d. In section 21 a between 420 nm and 720 nm, which is the visible wavelength range, transmittance is everywhere higher by about 20 % than that of the curve 22 of a non-coated substrate. At 1530 to 1550 nm, the wavelength of so-called "eye-safe" LIDARs or range finders, the transmittance profile has another section 21 b which has a peak of well over 90 % at that wavelength and thus is also by about 20 % higher than the transmittance of the non-coated substrate. The transmittance of a substrate coated according to the invention exhibits a further section of high transmittance, which rises steeply at a wavelength of about 3000 nm. At a wavelength of about 13,000 nm, the transmittance drops steeply. Typically, two wavelength ranges are used in this region of technical applications, first the range 21 c from 3500 nm to 5000 nm for detecting objects of high-temperature, such as jet engines or internal combustion engines, and second the range 21 d from 7500 nm to 11500 nm for detecting body temperature. In these two ranges, the transmittance profile 21 of the coated substrate also exhibits a transmittance that is higher by about 20 % than the curve 22 of the non-coated substrate.Thus, the coating is a 4-band anti-reflection coating. It is transparent and has an anti-reflection effect in wavelength ranges in the visible spectral range, for a so-called "eye safe" range finder, as well as for heat radiation of engines and living bodies.

The example of a coating according to the invention consists of the three layer materials YF3, ZnS and HfO2. In the discussed example, the three layer materials have the following refractiveindices:Material Coating technology Refractive index @ 1000 nmYF3 Electron beam 1.49ZnS Electron beam 2.28HfO2 Electron beam 1.90HfO2 Ion Plating 2.11 17SGL0242ILPSCHOTT AGP 4713IL The last two layers in this example are each made of HfO2. However, the first half is deposited by a standard electron beam vapor deposition process (electron beam). The second half is deposited by ion plating. In this way, the last non-oxidic layer is protected, by the first HfOsublayer, from the ion plating process which would damage the underlying non-oxidic layer and degrade its transmittance or absorbance in the sense of the invention. The layer structure is as follows: Substrate, 20.1 nm YF3, 36.1 nm ZnS, 60.3 nm YF3, 25.8 nm ZnS, 42.7 nm YF3,243.6 nm ZnS, 168.5 nm YF3, 89.2 nm ZnS, 170.2 nm YF3, 46.1 nm ZnS, 35.6 nm HfO2 (electron beam), 35.6 nm HfO2 (ion plating), air. The result of a double-sided coating with this design on a ZnS substrate of 10 mm thickness is the measured transmittance spectrum 21.

FIG. 3 shows an embodiment in which an additional adhesion promoting layer 6 is applied to the substrate 1 in order to enhance the adhesion of the layer stack 2 to the substrate 1. This adhesion promoting layer 6 is generally characterized by the fact that it adheres better on the substrate 1 than a layer 5 of the third type. According to a first embodiment of the invention, the adhesion promoting layer 6 may be kept thin enough to not or only marginally influence the reflection properties of the layer stack in optical terms. Preferably, the layer thickness is preferably at least 1 nm and/or preferably less than 10 nm in this case. With a thin layer, it is more generally also possible to use a material which has a higher absorption coefficient in the visible and/or infrared spectral range than the materials of the first, second, and third types, because due to the small layer thickness the total transmittance would not be significantly reduced. A suitable material for the adhesion promoting layer, which provides high adhesion to many substrate materials, is aluminum oxide, Al2O3.

According to yet another embodiment of the invention, the adhesion promoting layer 6 may at the same time be an optically active constituent of the layer stack 2, which contributes to the antireflection effect. For this purpose, the adhesion promoting layer 6 may in particular be a layer of the second type.

In the embodiment according to FIG. 4, the uppermost layer 7 is divided into a second sublayer and a first sublayer 12, wherein the first sublayer 12 defines the surface of the layer stack 2. The second sublayer 11 is applied without an assisting ion or plasma process, for the deposition of the first sublayer 12 such an assisting process is used. In this way, it is avoided that during the 17SGL0242ILPSCHOTT AGP 4713IL ion-assisted deposition process the high-energy ions damage the underlying layer 4 of the first type chemically or physically. By contrast, the ion assist results in a dense layer structure of the first sublayer 12. So, although the two sublayers 11, 12 are made of the same material, they differ in terms of their density. Typically, the first sublayer 12 will have a greater density and thus also a greater refractive index. The ionic assist results in a dense and resistant surface.

In the embodiment according to FIG. 5, an additional protective layer 13 is applied below or prior to the uppermost layer 7, in order to protect the material of the layer 4 during the deposition of the uppermost layer 7 against the ion or plasma process. Accordingly, it is generally contemplated in this embodiment that the protective layer is deposited prior to the uppermost layer 7, and that the uppermost layer 7 is deposited on the protective layer and in contact therewith.

In the embodiment according to FIG. 6, the optical component 10 includes an alternating layer system in which layers 4 made of the material of the first type alternate with layers 5 made of the material of the third type. Layers 4 have a thickness that is greater than the thickness of thelayers 5 by at least a factor of 10. The latter layers in the form of very thin intermediate layers are also referred to as "needle layers".

In the embodiment according to FIG. 7, one of the two layers 4 is implemented as a so-called nanolaminate 50. This layer includes a plurality of successive thin layers with thicknesses between 2 nm and 10 nm.

The coating according to the invention was subjected to two standard tests to verify its scratch resistance or abrasion resistance. The first standard test was the so-called Bayer test according to ASTM F735-11, TABER. The abrasive medium used in this case was silica sand which has the following properties: Grading 5/9Roundness 0.6+Sphericity 0.6+Hardness 7.0S.G. 2.65 17SGL0242ILPSCHOTT AGP 4713IL 0.12800°/3100° brown / white 6.9 - 7.0 Loss on ignitionMPColor pH The typical chemical composition of the silica sand used is as follows, in percent by weight: SiO2 99.48 wt%Fe2O3 0.06 wt%Al2O3 0.21 wt%MgO < 0.01 wt% Such silica sand is commercially available from Rimer Silica, Texas, U.S.A.

A further relevant test for such applications and coatings is the so-called windshield wiper test, sometimes referred to as washability test, according to the TS1888 standard. The coated sample is mounted in a holder, and the outer coated surface is subjected, during 5 minutes, to 1000 wiper cycles per hour (2000 passes per hour) by a standard automotive windshield wiper lip with a wiper load of 20 grams per centimeter under addition of a mixture of sand and water (1 cm3 of sand according to DEF STAN 07-55 type C in 10 milliliters of water).

At the end of the test, the sample must not show any visible signs of scratching when visually inspected.

In this test, a standard coating with a fluoride as the uppermost final layer was reduced in its layer thickness by an average (macroscopically viewed) of 70 nm, while the reduction in thickness of the coating according to the invention was only 12 nm on average (macroscopically viewed). Both coatings exhibited the same spectral specification. To analyze these reduced layer thicknesses, reverse engineering was carried out on the optical layer design of the reflection spectra measured before and after the abrasion. 17SGL0242ILPSCHOTT AGP 4713IL As a further standard test for verifying the abrasion resistance, the windshield wiper test according to the standard TS1888 was employed with dirty water. In this case, the windshield wiper exerts a pressure of 22 N and performs 100 movements per minute over an angular range of 60 degrees. The percentage alteration in haze is measured at appropriate intervals according to the ASTM D1003 standard. Once the average haze value of the medium field of view reaches %, this is generally considered as the end of the service life.

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

The measurement of abrasion resistance is performed such that at least one of the following parameters is measured prior to and after carrying out at least one of the described test methods: - 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 predefined range of wavelengths;- transmittance in a predefined range of wavelengths; or- distinctness of the image (DOI) transmitted through the component.

When an optical component according to the invention is compared with a component having the same substrate material and a coating that is comparable with respect to its optical behavior, but in which the uppermost layer is made of a fluoride, a significant improvement in abrasion resistance is resulting for a component according to the invention. Compared to an optical component that has an uppermost fluoride layer as mentioned above, it is apparent that, although the aforementioned parameters (amount and size of surface defects according to ISO10110, etc.) also deteriorate for an optical component according to the invention, this deterioration is at least % less than in the case of the optical component with uppermost fluoride layer.

It will be apparent to those skilled in the art that the invention is not limited to the exemplary embodiments illustrated in the figures, but may rather be varied within the scope of the subject 17SGL0242ILPSCHOTT AGP 4713IL matter of the claims. The features of the individual exemplary embodiments may in particular be combined with each other. 17SGL0242ILP List of Reference Numerals SCHOTT AG 25P 4713IL 1 SubstrateLayer stack3 Layer of second typeLayer of first typeLayer of third typeAdditional adhesion promoting layerUppermost layer9 Lowermost layerOptical componentSecond sublayer of 7First sublayer of 7Additional protective layer21a, b, c, d Transmittance profile with anti-reflection coatingTransmittance profile without anti-reflection coatingNanolaminate

Claims

1. 26 267969/

2. Claims: 1. An optical component (10), comprising a substrate (1) provided with a layer stack (2) including a plurality of successive layers of different materials and different refractive indices, which defines an anti-reflection coating, wherein the layers of the layer stack (2) are made from at least three different materials or material combinations, so that the layer stack contains at least one layer of each of a first type, second type, and third type, with at least three different refractive indices, wherein a layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than a layer of the second type; and wherein an uppermost layer and a second uppermost layer are provided, wherein the uppermost layer (7) is a layer of the second type (3) and the second uppermost layer is a layer of the first type (4) and thus has a refractive index which is higher than the refractive index of the uppermost layer; and wherein the layer stack (2) includes at least one further layer which is disposed below the two uppermost layers within the layer stack (2) and which is 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, and wherein the layer (4) having the highest refractive index is made of the same material as the substrate (1). 2. The optical component (10) as claimed in the preceding claim, wherein the uppermost layer is an oxide layer.

3. The optical component (10) as claimed in any one of the preceding claims, wherein the layer stack (2) is formed as an alternating layer system comprising alternating layers of the first and third types and a layer of the second type as the uppermost layer.

4. The optical component (10) as claimed in any 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) forming the uppermost layer of the layer stack (2). 27 267969/

5. The optical component as claimed in any one of the preceding claims, wherein the layer stack (2) comprises an adhesion promoting layer (6) that exhibits better adhesion to the substrate (1) than a layer of the third type, optionally wherein the adhesion promoting layer (6) is made of a material selected from the group comprising aluminum oxide and hafnium oxide, or is a layer of the second type.

6. The optical component as claimed in any one of the preceding claims, wherein the uppermost layer (7) comprises a first sublayer (12) and a second sublayer (11) of the same material, but with a different refractive index.

7. The optical component as claimed in any one of the preceding claims, wherein the coating comprises an alternating layer system in which layers of two types alternate, wherein the layers of one type are thicker than the layers of the other type, wherein at least one of the following features applies: - the alternating layer system preferably comprises a total of at least four successive layers; - the layers of the one type are at least ten times thicker than the layers of the other type; - the thin layers are layers of the third type and the thick layers are layers of the first type. - the thin layers have a thickness between 2 nm and 50 nm.

8. The optical component as claimed in any one of the preceding claims, wherein at least one of the layers of the layer stack (2) is a nanolaminate made of a multitude of layers with thicknesses between 2 nm and 10 nm, and wherein these layers are made of at least two alternating materials.

9. The optical component (10) as claimed in any one of the preceding claims, wherein the substrate (1) and the layer stack (2) are at least partially transparent in the infrared and visible spectral range. 28 267969/

10. The optical component as claimed in any one of the preceding claims, wherein the substrate and the layer stack are at least partially transparent in the following wavelength range: - in the wavelength range from 450 nm to 650 nm.

11. The optical component (10) as claimed in any one of the preceding claims, wherein the substrate (1) is made of zinc sulfide or zinc selenide.

12. The optical component (10) as claimed in any one of the preceding claims, wherein the layer of the second type (3) is made of a material selected from the group comprising hafnium oxide (HfO 2), scandium oxide (Sc 2O 3), zirconium oxide (ZrO 2), tantalum oxide (Ta 2O 5), niobium oxide (Nb 2O 5), yttrium oxide (Y 2O 3), titanium oxide (TiO 2), aluminum oxide (Al 2O 3), cerium oxide (CeO 2), and mixtures thereof.

13. The optical component (10) as claimed in any one of the preceding claims, wherein the further layer (5) is a fluoride layer, or wherein the further layer (5) is made of a fluoride selected from the group comprising 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.

14. The optical component (10) as claimed in any one of the preceding claims, wherein the uppermost layer (3) is applied by a different process than the other layers of the layer stack (2).

15. The optical component (10) as claimed in any one of the preceding claims, wherein the layer stack (2) comprises an alternating layer sequence which includes at least one further layer made of the same material as one of the three uppermost layers.

16. The optical component (10) as claimed in any one of the preceding claims, wherein the lowermost layer (9) is a layer of the third layer type having the lowest refractive index. 29 267969/

17. The optical component (10) as claimed in any one of the preceding claims, wherein the layer stack (2) comprises a total number of layers between seven and thirty.

18. The optical component (10) as claimed in any one of the preceding claims, wherein the optical component exhibits no visible signs of surface scratches after a windshield wiper test in compliance with test standard TS1888, and preferably the amount of surface defects according to ISO10110 is reduced by at least 20 % compared to an optical component having a fluoride layer as an uppermost layer.

19. A method for producing an optical component (10) with an anti-reflection coating, wherein a substrate (1) is provided with a layer stack (2) including a plurality of successive layers of different materials and different indices of refraction, which defines an anti-reflection coating, wherein the layers of the layer stack (2) are successively deposited from at least three different materials or material combinations so that the layer stack created by the successive deposition contains at least one layer of each of a first type, second type, and third type, with at least three different refractive indices, wherein a layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than a layer of the second type; and wherein an uppermost layer and a second uppermost layer are provided, wherein the uppermost layer (7) is a layer of the second type (3) and the second uppermost layer is a layer of the first type (4) and thus has a refractive index which is higher than the refractive index of the uppermost layer; and wherein the layer stack (2) includes at least one further layer which is disposed below the two uppermost layers within the layer stack (2) and which is 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 and wherein the layer (4) having the highest refractive index is made of the same material as the substrate (1).

20. The method as claimed in the preceding claim, wherein the layer of the second type (3) is applied by a process selected from the group comprising ion plating, ion implantation, ion assist/advanced plasma, magnetron sputtering, ion beam sputtering, cathodic arc deposition, and atomic layer deposition. 30 267969/

21. The method as claimed in the preceding claim, wherein the layer of the second type is applied in the form of two sublayers (11, 12), wherein the second sublayer (11) is applied without a supporting plasma or ion process and the first sublayer (12) is applied using a supporting plasma or ion process.

22. The optical component (10) as claimed in any one of claims 1 to 18, for use in a single-spectrum or multi-spectral visible range and infrared range of the electromagnetic spectrum.