Patent Application
20180299587
This description pertains to optical elements for infrared applications. More particularly, this description pertains to optical elements with anti-reflection coatings that exhibit high transmittance at infrared wavelengths. Most particularly, this description pertains to adhesion layers for improving adhesion of infrared anti-reflection coatings on infrared-transmitting substrates.
Infrared optical systems are essential to many technologies. Common applications of infrared optical systems include night vision systems, thermal cameras, motion control systems, astronomy, lithography, heat loss detection, remote temperature sensing, process control, medical imaging, targeting and range finding, and infrared sensors.
The performance of infrared optical systems depends critically on the optical components used in the design of the system. Optical components include infrared light sources, reflective elements (e.g. mirrors), transmissive elements, and detectors. Transmissive elements include refractive elements (e.g. lenses) and windows. In order to insure optimal optical efficiency, transmissive elements need to exhibit high transmission over a wide range of infrared wavelengths. In particular, it is desirable to have transmissive elements that are highly transmissive over the short wavelength infrared range (SWIR; 1 μm-3 μm), medium wavelength infrared range (MWIR; 3 μm-8 μm), and long wavelength infrared range (LWIR; 8 μm-15.3 μm).
Optical elements for transmission and reflection in the infrared typically include a substrate and a coating. The substrate is a material having high reflectivity or high transmittance in the infrared. The coating is a series of one or more layers applied to one or more surfaces of the substrate and is designed to enhance the reflectivity or transmittance of the substrate. In the case of transmissive infrared optical elements, transmittance of the substrate is often significantly reduced by reflection of infrared radiation from the surface. High surface reflectivity from the substrate leads to lost infrared intensity and lower transmittance through the substrate.
One strategy for minimizing surface reflectivity from transmissive infrared substrates is to apply an anti-reflection coating to the surface. Anti-reflection coatings are single or multilayer coatings that are designed to have low reflectivity. When applied to a substrate surface, reflectivity of the anti-reflection coating is lower than the reflectivity of the substrate surface in the absence of the anti-reflection coating and higher transmittance through the substrate results.
Implementation of anti-reflection coatings for transmissive infrared optical elements can be challenging, however, because of a limited selection of materials. Relatively few substrate materials exhibit high transmittance over a wide range of infrared wavelengths and relatively few materials provide good anti-reflection characteristics over a wide range of infrared wavelengths. A further complication arises because of need for good adhesion of the anti-reflection coating to the substrate. Good adhesion is needed to insure durability of the anti-reflection coating to the substrate. The limited range of infrared substrate materials and anti-reflection materials in the infrared makes it difficult to achieve infrared optical elements with high transmittance. There is a need for transmissive infrared optical elements with durable anti-reflection coatings. There is also a need for coatings for use in band pass filters and beam splitters throughout the infrared.
An optical element that features high transmission and low reflectivity at infrared wavelengths is described. The optical element includes a substrate, an adhesion layer on the substrate, and an anti-reflection coating. Substrates include chalcogenide glasses, InAs, and GaAs. Adhesion layers include Se, ZnSe, Ga2Se3, Bi2Se3, In2Se3, ZnS, Ga2S3 and In2S3. Anti-reflection coatings include one or more layers of DLC (diamond-like carbon), ZnS, ZnSe, Ge, Si, HfO2, Bi2O3, GdF3, YbF3, YF3, and In2Se3. The optical elements show high durability and good adhesion when subjected to thermal shocks, temperature cycling, abrasion, and humidity.
The present disclosure extends to:
An optical element comprising:
a substrate, said substrate comprising a material selected from the group consisting of chalcogenide glass, InAs, and GaAs;
an adhesion layer on said substrate, said adhesion layer comprising a material selected from the group consisting of Si, Ge, a chalcogenide material, and a pnictide material; and
an anti-reflection coating on said adhesion layer, said anti-reflection coating comprising a first layer, said first layer comprising a material selected from the group consisting of ZnS, ZnSe, Ge, Si, HfO2, Bi2O3, GdF3, YbF3, YF3, In2Se3, and diamond-like carbon.
The present disclosure extends to:
An optical element comprising:
a substrate, said substrate comprising a material selected from the group consisting of chalcogenide glass, InAs, and GaAs;
a first layer on said substrate, said first layer comprising Se; and
a second layer on said first layer, said second layer comprising Ge.
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings are illustrative of selected aspects of the present description, and together with the specification serve to explain principles and operation of methods, products, and compositions embraced by the present description. Features shown in the drawing are illustrative of selected embodiments of the present description and are not necessarily depicted in proper scale.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the written description, it is believed that the specification will be better understood from the following written description when taken in conjunction with the accompanying drawings, wherein:
The embodiments set forth in the drawings are illustrative in nature and not intended to be limiting of the scope of the detailed description or claims. Whenever possible, the same reference numeral will be used throughout the drawings to refer to the same or like feature.
The present disclosure is provided as an enabling teaching and can be understood more readily by reference to the following description, drawings, examples, and claims. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the embodiments described herein, while still obtaining the beneficial results. It will also be apparent that some of the desired benefits of the present embodiments can be obtained by selecting some of the features without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations are possible and can even be desirable in certain circumstances and are a part of the present disclosure. Therefore, it is to be understood that this disclosure is not limited to the specific compositions, articles, devices, and methods disclosed unless otherwise specified. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
“Include,” “includes,” or like terms means encompassing but not limited to, that is, inclusive and not exclusive.
The term “about” references all terms in the range unless otherwise stated. For example, about 1, 2, or 3 is equivalent to about 1, about 2, or about 3, and further comprises from about 1-3, from about 1-2, and from about 2-3. Specific and preferred values disclosed for compositions, components, ingredients, additives, and like aspects, and ranges thereof, are for illustration only; they do not exclude other defined values or other values within defined ranges. The compositions and methods of the disclosure include those having any value or any combination of the values, specific values, more specific values, and preferred values described herein.
The indefinite article “a” or “an” and its corresponding definite article “the” as used herein means at least one, or one or more, unless specified otherwise.
As used herein, contact refers to direct contact or indirect contact. Direct contact refers to contact in the absence of an intervening material and indirect contact refers to contact through one or more intervening materials. Elements in direct contact touch each other. Elements in indirect contact do not touch each other, but are otherwise joined to each other through one or more intervening elements. Elements in contact may be rigidly or non-rigidly joined. Contacting refers to placing two elements in direct or indirect contact. Elements in direct (indirect) contact may be said to directly (indirectly) contact each other.
As used herein, the term “on” refers to direct or indirect contact. If one layer is referred to herein as being on another layer, the two layers are in direct or indirect contact.
Reference will now be made in detail to illustrative embodiments of the present description.
The present description provides optical elements that exhibit high transmittance in the infrared spectral region. The optical elements include a substrate, an anti-reflection coating, and an adhesion layer between the substrate and anti-reflection coating. The adhesion layer increases the strength of adhesion of the anti-reflection coating to the substrate to provide a more durable transmissive infrared optical element. Inclusion of the adhesion layer leads to transmissive infrared optical elements that remain stable when subjected to thermal shock (e.g. exposure to liquid nitrogen), temperature cycling (e.g. cycling back and forth between 200° C. and −196° C.), humid conditions, and abrasion. The improved adhesion inhibits delamination of the anti-reflection coating when the optical element is subjected to thermal and mechanical loads.
The substrate material is a chalcogenide glass, InAs, or GaAs. Chalcogenide glasses include Se-containing glasses, such as glasses in the Ge—As—Se, As—Se, Ge—Sb—Se, and As—Se—Te families. Preferred chalcogenide glasses include AsxSe100-x (0<x<100), examples of which include As40Se60. Representative commercial chalcogenide glasses include IRG series of glasses from Schott North America, Inc. (Duryea, Pa.), the IG series of glasses from Vitron Spezialwerkstoffe GmbH (Jena, Germany), and the AMTIR series of glasses from Amorphous Materials, Inc. (Garland, Tex.). Other substrate materials include Ge, BaF2, and ZnSe.
Adhesion layers include chalcogenide materials, pnictide materials, Si and Ge. Chalcogenide materials include Se, ZnSe, Ga2Se3, Bi2Se3, and In2Se3. Pnictide materials include Ga2S3, ZnS, and In2S3.
The anti-reflection coating is a single layer coating or multiple layer coating. Materials for the one or more layers in the anti-reflection coating include DLC (diamond-like carbon, an amorphous carbon material having a hardness similar to diamond), ZnS, ZnSe, Ge, Si, HfO2, Bi2O3, GdF3, YbF3, YF3 and In2Se3. In one embodiment, the anti-reflection coating is a single layer of DLC. In other embodiments, the anti-reflection coating includes an alternating series of higher index layers and lower index layers. In one embodiment, the anti-reflection coating has a periodic layer structure that includes one or more periods, where each period includes a higher index layer and a lower index layer. The composition and/or thickness of the higher index layer may be the same or different in each of two or more periods. The composition and/or thickness of the lower index layer may be the same or different in each of two or more periods. The number of periods in the coating is one or more, two or more, three or more, four or more, five or more, or in the range from 1-100, or in the range from 2-80, or in the range from 3-70, or in the range from 4-60, or in the range from 5-50.
The number of layers in a period is two, three, four, five, six, or in the range from 2-20, or in the range from 4-10. Representative two-layer periods of medium index (e.g. 1.6-2.6)/low index (e.g. 1.3-1.6) materials for the anti-reflection coating include ZnS/YF3, ZnS/YbF3, ZnSe/YF3, ZnSe/YbF3. Representative three-layer periods of high index (e.g. 2.6-4.4)/medium index (e.g. 1.6-2.6)/low index (e.g. 1.3-1.6 materials for the anti-reflection coating include Ge/ZnS/YF3, Ge/ZnSe/YF3, Ge/ZnS/YbF3, and Ge/ZnSe/YbF3. Other high index materials include Si. Other medium index materials include MgO2, Al2O3, HID2, Nb2O3, and Si3N4. Other low index materials include metal fluorides, such as LaF3, GdF3, LiF, MgF2, and BaF2.
The anti-reflection coating is in direct or indirect contact with one or more surfaces of the substrate material. In one embodiment, an adhesion layer is in direct or indirect contact with one or more surfaces of the substrate and the anti-reflection coating is formed on the adhesion layer. In one embodiment, the anti-reflection layer is in direct contact with the adhesion layer. In another embodiment, the anti-reflection layer is in indirect contact with the adhesion layer. In other embodiments, two or more adhesion layers are in direct or indirect contact with one or more surfaces of the substrate and the anti-reflection coating is in direct or indirect contact with at least one of the two or more adhesion layers. The two or more adhesion layers differ in composition. In one embodiment, a first adhesion layer is in direct contact with a surface of the substrate, a second adhesion layer is in direct contact with the first adhesion layer, and an anti-reflection coating is in direct contact with the second adhesion layer.
Representative optical elements include the following:
The thickness of the adhesion layer is in the range from 50 nm-500 nm, or in the range from 100 nm-450 nm, or in the range from 150 nm-450 nm, or in the range from 200 nm-400 nm.
The thickness of individual layers in the anti-reflection coating or the periods of the anti-reflection coating is in the range from 10 nm-5000 nm, or in the range from 10 nm-3000 nm, or in the range from 10 nm-2000 nm, or in the range from 100 nm-4000 nm, or in the range from 250 nm-4000 nm, or in the range from 10 nm-1000 nm, or in the range from 50 nm-1000 nm, or in the range from 100 nm-1000 nm, or in the range from 200 nm-1000 nm, or in the range from 350 nm-1000 nm, or in the range from 50 nm-750 nm, or in the range from 75 nm-500 nm, or in the range from 100 nm-400 nm, or in the range from 10 nm-100 nm, or in the range from 25 nm-100 nm.
The layer in the sequence of layers that is furthest from the substrate interfaces with air or other external ambient. In one embodiment, the layer furthest from the substrate is a layer in the anti-reflection coating. In another embodiment, the layer furthest from the substrate is a separate layer (e.g. a protective layer) that is in direct or indirect contact with the anti-reflection coating. Protective layers include DLC, YF3, YbF3, Bi2O3, HfO2, and GdF3. When DLC is used as a protective layer, an adhesion layer (e.g. Si or Ge) is optionally included between the DLC layer and anti-reflection coating.
The optical elements provide high transmission at infrared wavelengths. The transmission (measured as % Transmission (% T) per mm thickness at room temperature) of the optical element is greater than 60% over the wavelength range from 2.0 μm-12.0 μm, or greater than 70% over the wavelength range from 2.0 μm-12.0 μm, or greater than 80% over the wavelength range from 2.0 μm-12.0 μm, or greater than 85% over the wavelength range from 2.0 μm-12.0 μm, or greater than 90% over the wavelength range from 3.5 μm-5.0 μm, or greater than 90% over the wavelength range from 3.7 μm-4.5 μm, or greater than 90% over the wavelength range from 6.0 μm-11.0 μm, or greater than 90% over the wavelength range from 6.5 μm-10.5 μm, or greater than 90% over the wavelength range from 7.0 μm-10.0 μm, or greater than 92% over the wavelength range from 3.5 μm-5.0 μm, or greater than 92% over the wavelength range from 3.7 μm-4.5 μm, or greater than 90% over the wavelength range from 6.0 μm-11.0 μm, or greater than 92% over the wavelength range from 6.5 μm-10.5 μm, or greater than 92% over the wavelength range from 7.0 μm-10.0 μm, where thickness refers to the total thickness of the optical element including the substrate thickness and the thickness of all layers on the substrate.
The optical elements provide high transmission at infrared wavelengths. The transmission (measured as % Transmission (% T) per mm thickness at 77 K) of the optical element is greater than 60% over the wavelength range from 2.0 μm-12.0 μm, or greater than 70% over the wavelength range from 2.0 μm-12.0 μm, or greater than 80% over the wavelength range from 2.0 μm-12.0 μm, or greater than 85% over the wavelength range from 2.0 μm-12.0 μm, or greater than 90% over the wavelength range from 3.5 μm-5.0 μm, or greater than 90% over the wavelength range from 3.7 μm-4.5 μm, or greater than 90% over the wavelength range from 6.0 μm-11.0 μm, or greater than 90% over the wavelength range from 6.5 μm-10.5 μm, or greater than 90% over the wavelength range from 7.0 μm-10.0 μm, or greater than 92% over the wavelength range from 3.5 μm-5.0 μm, or greater than 92% over the wavelength range from 3.7 μm-4.5 μm, or greater than 90% over the wavelength range from 6.0 μm-11.0 μm, or greater than 92% over the wavelength range from 6.5 μm-10.5 μm, or greater than 92% over the wavelength range from 7.0 μm-10.0 μm, where thickness refers to the total thickness of the optical element including the substrate thickness and the thickness of all layers on the substrate.
The optical elements provide low reflectance at infrared wavelengths. The reflection (measured as % Reflection (% R) at room temperature at an angle of incidence of 10°) of the optical element is less than 20% over the wavelength range from 4.0 μm-10.0 μm, or less than 15% over the wavelength range from 5.0 μm-10.0 μm, or less than 10% over the wavelength range from 3.0 μm-6.0 μm, or less than 5% over the wavelength range from 7.0 μm-10.0 μm, or less than 5% over the wavelength range from 3.5 μm-5.0 μm, or less than 4% over the wavelength range from 7.0 μm-10.0 μm, or less than 4% over the wavelength range from 3.7-4.7 μm, or less than 3% over the wavelength range from 7.2 μm-10.0 μm, or less than 3% over the wavelength range from 3.7 μm-4.5 μm, or less than 2% over the wavelength range from 7.5 μm-10.0 μm, or less than 1% over the wavelength range from 8.0 μm-9.5 μm.
The optical elements provide low reflectance at infrared wavelengths. The reflection (measured as % Reflection (% R) at 77 K at an angle of incidence of 10°) of the optical element is less than 20% over the wavelength range from 4.0 μm-10.0 μm, or less than 15% over the wavelength range from 5.0 μm-10.0 μm, or less than 10% over the wavelength range from 3.0-6.0 μm, or less than 5% over the wavelength range from 7.0 μm-10.0 μm, or less than 5% over the wavelength range from 3.5 μm-5.0 μm, or less than 4% over the wavelength range from 7.0 μm-10.0 μm, or less than 4% over the wavelength range from 3.7 μm-4.7 μm, or less than 3% over the wavelength range from 7.2 μm-10.0 μm, or less than 3% over the wavelength range from 3.7 μm-4.5 μm, or less than 2% over the wavelength range from 7.5 μm-10.0 μm, or less than 1% over the wavelength range from 8.0 μm-9.5 μm.
Techniques for depositing adhesion layers and layers of the anti-reflection coating include sputtering, physical vapor deposition, and electron beam evaporation. Before depositing layers on the substrate, the surface of the substrate in the following Examples was cleaned and polished. Photosensitive substrates (e.g. As—Se glasses) were protected from UV exposure. Oxygen-sensitive glasses were protected from exposure to oxygen. Surface cleaning consisted of treatment with a solvent (e.g. alcohol) to remove debris and surface contamination. Polishing was completed with a polish pad treated with a wet slurry (e.g. 0.5 μm Al2O3 slurry in glycol) followed by a solvent (e.g. alcohol) rinse.
Tests of the durability of each of the three samples shown in
After completion of the liquid nitrogen immersion cycles, the samples were tested for adhesion and moderate abrasion using procedures outlined in the Mil-C-48497A test protocol. In the Mil-C-48497A adhesion test, 0.5 inch wide cellophane tape (conforming to Type I of L-T-90) was pressed firmly against the coated surface each of the samples and quickly removed at an angle normal to the coated surface. The samples were then visually inspected for delamination or other damage to the coating. None was observed, indicating that each of the three samples passed the adhesion test. After completion of the adhesion test, the samples were subjected to the Mil-C-48497A moderate abrasion test. In the moderate abrasion test, the coated surface of each of the three samples was rubbed with an abrader. Rubbing included 50 strokes directed in straight lines. The abrader was a pad (0.25 inch×0.375 inch) of clean, dry cheesecloth (conforming to standard CCC-C-440). The bearing force was a minimum of 1 pound and was applied normal to the coated surface. After rubbing, the samples were visually inspected for delamination or other damage to the coating. None was observed, indicating that each of the three samples passed the moderate abrasion test.
Each of the two samples was subjected to the humid environment, liquid nitrogen immersion cycling, adhesion test, and moderate abrasion test described above. Both samples passed the adhesion and moderate abrasion tests.
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the illustrated embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments that incorporate the spirit and substance of the illustrated embodiments may occur to persons skilled in the art, the description should be construed to include everything within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/484,447 filed on Apr. 12, 2017 the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62484447 | Apr 2017 | US |
