The interference coating

 

(57) Abstract:

The coating consists of alternating layers with a low value of the refractive index of magnesium fluoride and high refractive index of a material which is transparent in the infrared region and having a refractive index of not less than 2.2 and compressive stresses in the layer. In the middle layer MgF2put a layer of silicon dioxide. Layer is 0.2 to 0.5 optical thickness of the layer MgF2due to a corresponding reduction in its thickness. Layers with high refractive index can be made of zinc sulfide or zinc selenide or sulphide of antimony, or arsenic sulfide or arsenic selenide. On the outer layer of a material with high refractive index can be applied to the protective half-wave layer of low refractive index. The protective layer consists of a quarter-wave layer MgF2with a layer of SiO2and a quarter-wave layer of SiO2. Ensures the long-wave expansion of the scope and improve performance. 2 C.p. f-crystals, 1 Il.

The invention relates to the field of optical instrument, in particular to interference coatings and can be used to create sergentia, including laser technology in the field of wavelengths from 0.4 to 9.0 μm.

Interference coatings are widely used in optical instruments including laser technology, providing the necessary optical and performance characteristics of optical components and systems. The most common (basic) design is a multi-layer coating of the type P (HB)nor P (HB)nwhere P is optically polished substrate, and N - alternating interference layers having relatively high and relatively low values of refractive index, respectively, n is the number of pairs of layers of type b and H.

One of the known multilayer interference coatings used in the visible and near IR regions is the design of the form P (ZnS - NaAlF6)nZnS, where ZnS zinc sulfide having a transparency range of 0.4 - 14,0 μm and a refractive index of 2.5 to 2.2, respectively; NaAlF6- cryolite having a transparency range of 0.2 - 14,0 mm and a refractive index of 1.35 and 1.33 /1/. This coating has the following advantages: occurs in a wide region of wavelengths from 0.4 to 14.0 microns, these film-forming materials are relatively inexpensive and layers of them can be half the options are low moisture resistance, the corresponding group 3 and low mechanical abrasion, the corresponding 3 group OSTS-1901-85 /2/, i.e., the coating prevents rubbing optical cloth with an organic solvent. In this construction, the moisture resistance is determined mainly by the cryolite, and the mechanical strength of mainly zinc sulfide, located outside.

With the development of vacuum technology for coating and related technology using electron beam evaporation (ELI) were obtained multilayer interference coatings based on refractory oxides /1/. The main advantages of such coatings are the best performance characteristics: high moisture resistance, abrasion resistance and radiation resistance. The main disadvantages of interference coatings of refractory oxides are not sufficiently far-field implementation (of 0.25 to 2.5 microns), and relatively high cost. Although the transparency of refractory oxides extends to 10 μm, for wavelengths of more than 2.5 μm multilayer coatings are mechanically unstable due to significant unbalanced mechanical stresses in the layers. The high cost of the coatings of logocreator consumable materials and the necessity of a more expensive vacuum installations equipped with ELI.

Known for the design of multilayer interference coatings (prototype) of the form P (ZnS-MgF2)nZnS, where MgF2-magnesium fluoride has a refractive index of 1.46 - 1.38 in transparency 0,115 to 10.0 μm, respectively. Practical implementation of this design is limited to a short region border transparency ZnS i.e., 0.4 µm in wavelength from 1.0 to 1.35 μm. The latter is defined by the mechanical resistance of the multilayer coating due to unbalanced tensile stresses in the layers MgF2. Multilayer coatings of this type correspond to group 2, the moisture resistance and group 3 mechanical strength /2/. The main advantage of this design before the first analog is a higher moisture resistance. The main disadvantages of this design are: insufficient far-field implementation and insufficient mechanical strength.

The aim of the invention is the extension of the working area in the long-wavelength direction and operational improvement at a low cost.

This goal is achieved by the fact that in the middle layer MgF2put a layer of silicon dioxide (SiO2), SOS Additional outer layer In the deposited poluvalmovye layer N, consisting of a quarter-wave layer type MgF2- SiO2- MgF2with the same ratios in thickness and a quarter-wave layer of SiO2. Layers of type b can be made of materials such as zinc selenide (ZnSe), sulphide of antimony (Sb2S3), sulphide of arsenic (As2S3), arsenic selenide (As2Sl3) or other transparent in the infrared region of the SIP, with a refractive index of not less than 2.2 and compressive mechanical stress in the layers.

In the drawing conditionally (in cross section) shows the design of the proposed interference coatings of the form P (HB)n2H, where: 1 - optically polished substrate, 2 - layers MgF2separated by a layer 3 of SiO2, 4 - ZnS layers, forming a periodic structure pattern mirrored finish with a number of pairs equal to n, on the outer layer of ZnS are quarter-wave layer MgF2- SiO2- MgF2and a quarter-wave layer of SiO2.

The present invention has the following essential features: multilayer interference coating consisting of alternating between the layers with high () and low (N) values of the refractive index, where the material layer is ZnS, and the material layer H - MgF2put a layer of silicon dioxide of a thickness of 0.2-0.5) from the total optical thickness of the layer H, due to a corresponding reduction in the thickness of the MgF2. The use of SiO2as the interference layer known /1/, transparency is (from 0.2 to 9.0) μm, and the refractive index (1,55-1,45), respectively. It is known that layers of SiO2obtained by vacuum technology, are compressive stresses. Layers MgF2a thickness of more than 0.1 μm have considerable tension strains and already a quarter-wave layer at a wavelength of 4 μm on the glass substrate) is destroyed by cracking. For the prototype the full consideration of internal stress (compressive ZnS and stretching for MgF2) are not performed and there is an excess tensile stresses, however, does not lead to destruction of the coating in the region of 0.4-to 1.35 μm. For large wavelengths multilayer coatings of this type are destroyed by cracking very quickly. The introduction of a layer of SiO2in the middle of the interference layer MgF2can significantly reduce tensile stress in the layer H and thereby to realize the compensation of mechanical stresses in a multilayer structure, the latter becomes fur the puff SiO2(0,2-0,5) effective refractive index layer H becomes (1,4-1,42) respectively, which is quite acceptable for multilayer interference structures with the aim of preserving its optical characteristics. The introduction of a layer of SiO2it is in the middle layer MgF2allows you to avoid incompatibility layers of ZnS and SiO2and thereby prevent destruction of the coating due to the low cohesive strength between them.

The specified region of the layer thicknesses of SiO2-(0,2-0,5)H chosen from considerations of providing mechanical stability of the interference coating as the visible and IR regions without a significant increase of the refractive index of the layer N. For the short-wave region, it is advisable to apply a layer of a thickness of 0.2-0.3) and longwave (5,0-9,0) μm, respectively (0.4 to 0.5), which is specified almost in the evaluation of the mechanical stability of multilayer coatings during thermal Cycling tests.

The second additional outer layer In the deposited protective poluvalmovye layer H, consisting (from layer b) of a quarter-wave layer type MgF2- SiO2- MgF2with the same ratios in thickness, and a quarter-wave layer of SiO2. To increase poverhnostnogo layer To cause the protective poluvalmovye layer of SiO2. With the same purpose on top of the layer, we have introduced poluvalmovye protective layer, however, its composition meets the requirement of the necessary cohesive strength of the layer and to demand compensation of the stresses in a multilayer structure.

The third layer may also be made of materials ZnSe, Sb2S3, As2S3, As2Se3or other transparent in the infrared region, having a refractive index higher than 2.2 and compressive mechanical stress in the layers. The above POM known in the literature as transparent in the infrared region. Similarly ZnS they have a compressive mechanical stress in the layers, and the values of their refractive index is superior to 2.2. With the aim of obtaining an optical or operational advantages over multilayer coatings with ZnS can be applied above the SIP.

Describes the distinctive characteristics form a new set of features is not known in the patent and technical literature.

The proposed solution is implemented in the following way. First determine theoretically or experimentally the parameters of a multilayer interference structure, i.e., determine the number and thickness of layers on the basis of the function is the second region of wavelengths on the basis of a design P/(MgF2- SiO2- MgF2) - ZnS/nor other SIP-type of the above. With regard to our recommendations experimentally clarify the required thickness of the layer of SiO2in the field of recommended values (0.2-0.5) H. If you need to have a high mechanical and radiation resistance, which is typical, for example, for laser mirrors, on top of the layer type, you must provide protective poluvalmovye layer consisting of a quarter-wave layer type MgF2- SiO2- MgF2and a quarter-wave layer of SiO2. Then produce a coating of vacuum technology using any method of controlling the thickness of layers in the coating process.

Practically, we have produced a quarter-wave laser mirrors for wavelengths 0,633, 1.06 and 1.5 μm on the substrate made of quartz glass and glass K-8 with a reflectivity of from 90 to 99.5%. In particular, "deaf" mirror coating at the wavelength of 1.06 μm had the following design P/(0,33 MgF20,33 SiO20,33 MgF2) - ZnS/7(0,33 MgF20,33 SiO20,33 MgF2) SiO2. The coating was applied to the domestic vacuum installing WU-IA using photometric control of the thicknesses of layers during the coating process. Cover imeokparia allowed RUB optical cambric cloth with an organic solvent. Radiation strength of the coating were close to the mirrors of the refractory oxide-based materials, zirconium oxide (ZrO2and SiO2.

In addition, there were experimental laser mirrors for wavelengths 3,39 and 5.5 μm on the substrate made of quartz glass KEY and zinc selenide coated with type P/(0,3 MgF20,4 SiO20,3 MgF2Sb2S3/2(0,3 MgF20,4 SiO20,3 MgF2) SiO2with a reflectivity of about 90%. In this case, as the layer used In the sulphide of antimony, which helped to reduce the number of layers in the mirror coating and thereby improve mechanical stability and to reduce cost. Moisture resistance and strength, wear coatings had the same characteristics as in the first case.

Thus, a multilayer interference (mirror) coating in accordance with the proposed invention has allowed to expand the scope of at least 5.5 μm and improve operating characteristics compared to the prototype, as compared with analogues of refractory oxides to extend the scope of the implement in the direction of the infrared radiation and to gain an advantage in the cost of at least 2-4 times.

/P>2. The industry standard, OSTS-1901-85.

3. P. P. Yakovlev, B. B. Sacks. Designing interference coatings. M.: Mashinostroenie, 1987.

1. The interference coating consisting of alternating between the layers with high and low values of refractive index, where the material layer with a low refractive index is magnesium fluoride (MgF2), characterized in that the layers with a high refractive index made of a material transparent in the infrared region and having a refractive index not less than 2.2 and compressive stresses in the layer and the middle layer MgF2put a layer of silicon dioxide (SiO2), component (0,2 - 0,5) optical thickness of the layer of low refractive index due to a corresponding reduction in the thickness of the layer MgF2.

2. The floor under item 1, characterized in that the layers with a high refractive index is made of zinc sulfide or zinc selenide or sulphide of antimony, or arsenic sulfide or arsenic selenide.

3. The floor under item 1 or 2, characterized in that the outer layer is made of a material with a high refractive index deposited protective poluvalmovye layer with a low refractive index, consisting start is on the layer of SiO2amounting to 0.2 to 0.5 optical thickness of this quarter-wave layer, and a quarter-wave layer of SiO2.

 

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