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known optical anomalies in monocrystals of germanium and paratellurita.

In crystals of germanium OA it is immediate in a visible gamut are not visible, but most rough of them are always localised in volumes of a material with a high dislocation density, as a rule, containing and MUT (malouglovye boundaries) [2, 60, 91].

On fig. 1.7 the surface is shown

Monocrystal of germanium in diameter of 300 mm, subjected to chemical selective etching and conventionally parted on sektory for the purpose of dislocation density calculation on material volume. Even it is visually good

Considerably, that in allocation of dislocation poles of etching there is an obvious

Non-uniformity - light fields correspond to small density

Dislocations, dark fields - a high dislocation density, and distinction of this quantity reach on a crystal not less the order - from IO4 to IO5см ' 2.

Fig. 1.7. Traversal section of the pickled monocrystal of the germanium, marked for the local analysis of a dislocation density

On fig. 1.8 the monocrystal of germanium with the oozed bands differing on structural and optical perfection is presented. The crystal had diameter 52 - 55 mm and length along an axis of growth of 300 mm. On section of the sample 4 fields, differing are oozed by structural perfection. Fields 1 and 2 were characterised by presence branched out malouglovyh boundaries (in the field of 1 - higher concentration malouglovyh boundaries). Fields 3 and 4 were characterised by presence of the rather uniformly distributed dislocations with their different density - in oblastiv

Fig. 1.8. A monocrystal of germanium in diameter of 52-55 mm with four oozed fields, differing a dislocation density and

Presence MUT (malouglovyh boundaries)

Interferometric examinations of the same sample of germanium on pass were spent on Ik-interferometer IR-80 constructed under plan Tvajmana-Grina with a control wave length of 10,6 microns. Visualisation of interferograms was carried out with the help pirovidikona with the subsequent input of data file about intensivnostjah in the computer.

Fig. 1.9. An interferogram of field of germanium with high density

The dislocations, gained on pass at a radiation wave length λ =10,6 microns

On fig. 1.9 the interference figure is given at the control on pass of the site corresponding to field 1 on fig. 1.8 from peak

5 2

Dislocation density (10 sm ') and the peak concentration malouglovyh boundaries.

The analysis of effects shows, that srednekvadraticheskaja wavefront strain (RMS) makes 0,115 λ, and the full scope (AN) - 0,40 λ. Optical heterogeneity (An) in the presented sample varies monotonously and is spotted on the full scope (AN) a zone error where h - a thickness of the sample.

Value of optical heterogeneity in the field of 1 has made In fields 2, 3 and 4 similar experiments have given

Calculations of mechanical voltages σ∣, v germanium, the cores on the values of variations of exponents of refractive Ap gained observationally, were yielded according to the formula (1.1).

Effects of calculations have shown, that the peak values of mechanical voltages in fields from the worst optical

Q

Homogeneity have made (4-5) ∙ 10 Pases in fields with the peak concentrations malouglovyh boundaries and with the peak dislocation density (the order of 10 sm '). The underload values of mechanical voltages (5-7) ∙ 10 Pases were observed in fields with the peak optical homogeneity and the underload dislocation density (the order of 5-10 sm ') in which miss malouglovye boundaries.

Thus, communication between the flaws of structure caused by them by mechanical voltages, and also electrophysical properties and optical anomalies in germanium monocrystals comes to light unequivocally enough at qualitative level, and by means of the interference methods can be gained numerically.

In monocrystals paratellurita many OA macrolevel and mesolevel come to light much easier thanks to a material transparency in a visible gamut.

Flaws of the polished surfaces of these crystals can be observed on screens and be fixed by numeral cabinets immediately on screens at illumination of optical devices dilated kollimirovannymi bundles of laser light as it is shown on fig. 1.10. Other, more precision expedient of examination of optical homogeneity of crystals paratellurita consists in use of the narrow, not conversed laser beams. At first the free beam is guided to an input window of the device «Laser Beam Profiler», the exit from which PZS-MATRIX in the form of pictorial dependence of intensity of radiation on co-ordinates in a plane (or along any co-ordinate axis) is observed on screen PC. Then the beam is passed in laser profilometr through an explored site of a crystal, the intensity lateral view then computer subtraction of the initial and garbled lateral views of intensity is yielded registers garbled in an optical device. It allows at qualitative level and quantitatively to estimate the contortions imported to a lateral view of a beam only OA, proper in a concrete crystal. Thus it is possible to spend measurings under the input aperture of an optical device. If the initial crystal in a view buli with propolished is cross-parallel "windows" on crystal opposite sides it is possible to choose in advance for subsequent use most opticheski the homogeneous volumes of a material is tested.

Have twisted in paratellurite are most in detail explored in operations [44, 45]. In them it is proved, that have twisted (fig. 1.12), correspond to those volumes of crystals in which it is sharp, on 1-2 orders the dislocation density in comparison with environmental volumes that is shown on fig. 1.13 is raised.

The dislocation density in the field of a crystal with svilju reaches values ~106см ' 2. In opticheski the homogeneous field of a crystal the dislocation density does not exceed 10 sm '. Bessvilnost crystals with the most advanced stage of the optical homogeneity, spotted according to STATE THAT 3522-81, should correspond to a category 1Б.

Fig. 1.10. Flaws and optical anomalies on the polished surface of a monocrystal paratellurita, observed in linearly-polarised

Laser light

Fig. 1.11. Caused OA contortions of the shape of a lateral view of intensity in section of the laser beam which has transited an optical device from a crystal paratellurita. Gaussian the shape - an initial beam. The garbled shape - the beam which has transited through a crystal

Fig. 1.12. Large svil, [001] crystals transiting in a direction

paratellurita. An observation direction - [110]

Fig. 1.13. Dislocation poles of etching of a site of a surface of a crystal paratellurita (an edge plane - (110)) in the field containing svil

Gas vials - flaws of structure, well-known even from the first experience on cultivation of crystals paratellurita from a melt a method Chohralsky [42-44,92]. On classification OA gas inserts can concern anomalies of all dimensional levels as diameters of vials lay in limits from several microns to 1-2 mm (fig. 1.). In
Communications with it data OA are well resolved by means of methods of classical microscopy. It is erected, that a material adjoining to fields with vials, it is free from mechanical voltages and does not differ the raised concentration of other structural flaws and OA - dislocations, MUG, blocks, major variations of exponents of a refractive. Optical activity of vials on transiting light close to activity of microscopic hollow scattering lenses, as a result of scattering a part of the light stream which has entered into a crystal that garbles images and worsens all optical parametres of devices. Requirements to puzyrnosti crystals paratellurita, as well as other crystals and glasses, are regulated GOST 3522-81 [93]. Materials optical. A definition method puzyrnosti.

It is considered, that for the majority of optical-acoustic devices and two-refractive prisms on the basis of crystals paratellurita there is enough category puzyrnosti ZG.

OA macrolevel in paratellurite abnormal is typical optical dvuosnost, characterised by a corner 2 V between the induced axes. The parent of this anomaly are residual poslerostovye the mechanical voltages garbling an optical indicatrix of a crystal. Abnormal dvuosnost comes to light an interferentsionno-polarisation method of a conoscopy at observation of the uniaxial crystals in a direction of an optical axis in a conical bundle of linearly-polarised light [94,95].

Fig. 1.14. Naturally located microvials in diameter 10-12 microns, and also anisomeric large gas inserts on boundary with volume without vials in a monocrystal paratellurita

Fig. 1.15. A crystal General view paratellurita with entrapped gas vials. And - peripheral field of a crystal without vials; In - field with the under concentration of vials; C - field of mass entrapment by a crystal of vials with the characteristic sectorial allocation on growth pyramids; D - narrow priosevaja field with the raised concentration of vials

Fig. 1.16. A large single bubble in diameter of 1,8 mm in a crystal paratellurita

Fig. 1.17. Display pezoopticheskogo the effect caused by mechanical voltages, in the form of abnormal dvuosnosti with a corner between the induced axes 2V~27 ', observed in konoskopicheskoj to a monocrystal pattern niobata the lithium, gained by means of laser radiation in a direction of an optical axis (f = 0) for volume at centre

(On an axis) buli. Two dark points - exits of the induced axes

Until recently for embodying konoskopicheskogo a method polarisation microscopes or polariscopes that restricted both the traversal sizes, and a thickness of tested samples were used only. Last years was extended also wide development a method of a laser conoscopy [96-102] in which as a radiant of linearly-polarised light the laser of the visible gamut which beam, after transformation to system of lenses or in a collimator, has the conical shape is used and a wide bundle transits through the major area of an input facet explored on dvuosnost a crystal. An example of use of a laser conoscopy is gained in the present operation konoskopicheskaja the monocrystal pattern niobata the lithium, presented on fig. 1.17. Advantages of such hardware registration of a method consist in possibility of observation isochrome (lines of an equal difference of a course of ordinary and unusual waves) much higher orders, than it is possible in microscopes. All konoskopicheskaja a pattern essentially is brighter and more accurate, than at observation in a microscope or a polariscope. Displaying laser konoskopicheskoj on the major semitransparent screen in gauge 1:1с the subsequent shooting by its numeral colour cabinet from a screen underside (towards to beams) allows to spend patterns then an exact numerical analysis of the gained images by means of computer program specially developed in the present operation. In the given program the exact equation isochrome of the uniaxial crystals on which warrant the theoretical pattern isochrome for a crystal of the given substance with known thickness pays off, with known main exponents of a refractive for an applied wave length of radiation and with a known corner between a normal line to a crystal and its optical axis is used recently output in author's operations [69, 71]. The theoretical pattern isochrome is compared to a pattern gained observationally that allows to explore all known
Types OA in paratellurite, including have twisted, variations of exponents of a refractive, abnormal dvuosnost.

The mechanical voltages giving an observable corner dvuosnosti, it is possible to calculate under the formula given in operation [95]:

Where π - tensor builders pezoopticheskih coefficients, σμ - builders of a tensor of mechanical voltages, V-half of corner between the induced axes.

Corner Rizm by which it is possible to measure immediately on the screen, allows to find and the true corner Vиз of the obvious approximate relation where - distance between points of an exit of optical axes on the screen, d - distance between a target surface of a crystal and the screen

- Refractive average index. In the explored crystal the corner of abnormal dvuosnosti made 27 ', that gives for mechanical voltages value ~ 40 Mna (4 kg/mm).

Theoretically abnormal dvuosnost always exists even at ideal from the practical point of view the uniaxial crystals, however observationally, at corners less than 2-3 ', it is behind a detection facet. It is considered, that performance of following requirements suffices for devices from the uniaxial crystals in the most sensitive to OA optoelektronnyh devices on dvuosnosti: in pripoverhnostnyh stratums of a crystal it should not exceed 30 ', in interior volumes — 20 '.

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A source: Tretjakov Sergey Andreevich. INFLUENCE of FLAWS of STRUCTURE And the MICRORELIEF of SURFACES ON OPTICAL HOMOGENEITY of MONOCRYSTALS. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver 2019. 2019

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  2. 1.6. Cultivation of monocrystals of germanium and paratellurita from a melt
  3. optical properties of large-sized monocrystals of germanium
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  5. Ivanov Alexander Ivanovna. Micromorphology of a surface and dislocation structure of large-sized optical crystals of germanium and paratellurita. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2015, 2015
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