The method of obtaining the interference layer

 

(57) Abstract:

Usage: to create the IR interference coatings for various applications. The inventive by evaporation from a single crucible evaporated material includes tellurium in amounts of 55 to 58 at.%, the rest is germanium, and the evaporation is carried out by an electron beam at a speed of condensation of not less than 7 nm/C.

The present invention relates to an optical instrument, in particular to the technology of optical coatings, and can be used to create interference coatings (PI) for various applications, including optical elements (OZ) IR laser systems.

PIS are widely used in optical instrumentation, including laser technology. So powerful technological CO2lasers are applied the output window and the resonator mirror with PI. Under the influence of powerful laser beams due to the presence of absorption in the FE part of the optical energy is converted into heat, stimulating the coating diffusion, recrystallization and mechanical stress, which leads to instability of the optical characteristics and fracture coatings.

As five of refraction (see for example, So-called. Krylov "Interference coatings", L. engineering, 1973). Practically it is known that the greater the number of layers in FE, the more optical loss and lower mechanical stability of the coating due to uncompensated internal mechanical stresses in the layers. The last significantly reduce the operating life of MA with IR, especially under the influence of powerful laser beams.

So, was highly reflective interference mirrors the number of layers can be reduced through the use of dielectric layers with a maximum difference of values of the refractive index. For IR FE this principle is particularly important, because it allows to significantly improve thermomechanical stability by reducing the number of layers.

Known IR film-forming materials (POM) with a relatively high value of the refractive index of ZnS, ZnSe, As2S3, As2Se3, Sb2S3, Ge, PbTe among Ge and PbTe have a maximum value of the refractive index in the region of 8-12 mcm,0 and 5.2, respectively, characterized by mechanical tension strains (see, for example, "Physics of thin films", edited by Huss, and others M the World, so 8, 1978, S. 36-46). When using Ge and PbTe as dielektricheskii who carried out their main disadvantage is the high value of acquisitions; 70 and 200 cm-1respectively(see for example the article Century. N. Glebova and other "Absorption in the layer interference coatings elements of the technological CO2lasers", RC, N 4, 1992, S. 56). In the technology of optical coatings known this POM as GATS, representing a compound Ge-30, As-17, Te-30, S-23 at. (see for example the article Takeo Mjata, "R&D of optics fo ew high power CO2lasers in the gapanese National Program", SPIE, 1986, v. 650, p.131-140). For the layers of the GATS are the following characteristics: n=3.1 and absorption = 2.5 cm-1(10.6 μm). The main disadvantage of this SIP is not a high value of refractive index (compared with Ge and PbTe), which significantly reduces its capability to create highly effective interference coatings for CO2-laser equipment.

In the Handbook (see for example Handbook the optical industri and systems directory, 1979) features information about SIP GeTe, which stated: mass density equal to 6.2 g/cm3the melting point of 725oC, evaporation temperature in vacuum (which creates the vapor pressure of 10-4Torr.) equal 381oC, other characteristics not included. In another source (see "Physics of thin films", M. Mir, I. 8, 1978, S. 52) has information about how to obtain films of compound AIIBVIand AIVthe m/c (prototype). Simplified write the chemical formula of compound type GeTe usually means that you used the connection with the composition of Ge50Te50at.

Studies of optical and physical characteristics of the films obtained by thermal evaporation in a vacuum connection GeTe containing Te 40 to 80 at. It is determined that the refractive index of the layers when the content of Te in the original POM 50 to 60 at. was equal to n=(3.7-3.8) for l10,6 μm (instead of 6.1 as stated in the source). It was also determined the dependence of the absorption layer from the initial SIP. For the composition of Ge50Te50absorption was 5-6 times less than for the Ge films, and thermal stability of these films did not exceed 80oC. At high temperatures is growing like a snowball absorption and destruction of the film. Taking into account the results of the main disadvantages of the prototype should be considered: the low thermal stability of the films and not enough low absorption, which does not allow to create a low-absorption and heat-stable interference coatings for technological CO2-laser systems.

The aim of the invention is to reduce absorption and increase thermal stability of the interference layers telluride GE is Noah germanium, and evaporation is carried out by an electron beam at a speed of condensation of not less than 7 nm/s

Study the process of obtaining layers of compounds GeTe showed that to achieve the minimum absorption is most effective electron-beam evaporation at much higher speeds condensation, which is explained by the following reasons. First connection passes into the vapor state, bypassing the liquid phase (sublimates). Secondly, the sublimation temperature is small (around 400oC). As a result, virtually no dissociation and interaction SIP with crucible material that at the constant speed of condensation leads to stabilization of the composition of the vapor phase, providing reproducible optical and physical characteristics of the obtained layers. Determined that the content of tellurium in the original POM 55-58 at. the absorption in the layers reaches 3 cm-1(which is very close to the absorption layers GATS).

The present invention has the following essential features of novelty. The first source material includes tellurium in amounts 55-58 at. the rest of germanium. Studies have shown, this optimal composition of the source material are achieved minimum absorption Gra in the initial SIP is a significant increase in absorption. Second evaporation to produce an electron beam (electron beam evaporation). By itself, this method is known in coating technology for a long time, but it combined with the properties of the original SIP allows to obtain reproducible optical and physical characteristics of the layers of telluride Germany. The use of resistive evaporation (as in the prototype) is not allowed to obtain layers with good performance. The third condensation rate is chosen not less than 7 nm/s, because at lower speeds there is an increase in absorption in the layers of telluride Germany, due to the increase of porosity due to zamurowywania molecules of the residual atmosphere in the chamber. After razacharovanij camera these pores saturated with moisture from the surrounding air, increasing the absorption. The maximum condensation rate is fundamentally not limited, however, this increases the "drip" faction in molecular flow, which degrades the optical purity of the coating. Almost sold condensation rate to 14 nm/s

Listed significant distinguishing features form a new set of features, not found in the technical and patent literature.

The suggested way of implementing what I tellurium containing tellurium 55 58 at. the rest of germanium. This material is in the form of granules are loaded into a crucible liner of glass carbon, which is installed in a water-cooled copper crucible electron beam evaporator type of WELI-1, part of the vacuum process installation of WU-1A or WU-2M. Further, in the camera working load of the substrate (polished plate), such as ZnSe. Luggage vacuumized to a pressure of not more than 410-4PA in the substrate, if necessary, heated to 100oC. Next, the source material receive sufficient outgassing under the flap, after which the emission current ELI increases to the set point, the valve open and put a layer of telluride Germany given thickness, for example, equal to a quarter wavelength, with a condensation rate of not less than 7 nm/s

On the basis of the proposed method have been developed and manufactured enlightening and beam splitter (mirror) interference coatings on optical elements of ZnSe for technological CO2-lasers. Made antireflection coating type PVN, consisting of quarter-wave layers GeTe and ZnSe, respectively. The coating had the following characteristics: coefficient of reflection from one surface r of 0.2% transmittance window with double-sided provolo all its characteristics up to 150oC. Another example of a fabricated beam-splitting coatings for output mirrors of the type ZnSe P auto gaseous VNV of GeTe and ZnSe, respectively, with the following characteristics: the reflection coefficient r 74% absorption b(0,01-0,02)%

Compare the characteristics of the above mentioned interference coatings obtained using layers telluride Germany, with similar functional coatings that use competing POM GATS. According to the calculated data for ar coatings of the form P GATS/ZnSe residual reflection from one surface is r3,2% of which clearly does not meet the requirements of laser optics (should be not more than 0.5%). To obtain the reflection coefficient of the beam-splitting coating r74% of the GATS and ZnSe necessary design of the form P (VL)3In having the seven quarter-wave layers instead of three (in our case). Naturally, such a coating should be more expensive, with large total losses and lower thermo-mechanical stability.

Thus, compared with the prototype of the proposed method allows to reduce the absorption in the layers telluride Germany 3-4 times and increase their thermostability of from 80 to 150oC.

Compared to competing POM GATS proposed method poses the gain a significant advantage due to the larger values of refractive index (3,7 instead of 3.1). The achieved characteristics of the layers of telluride Germany allow you to construct on the basis of more effective interference coatings for technological CO2laser systems compared to the GATS.

The method of obtaining the interference layer, including thermal evaporation in a vacuum from one crucible telluride Germany and condensation on the substrate, characterized in that the evaporated material includes tellurium 55 58 at. the rest of germanium, and the evaporation is carried out by an electron beam at a speed of condensation of not less than 7 nm/C.

 

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