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1.1. Classification of optical anomalies in crystals.

Optical anomalies (OA) - the extending term which rather has recently entered into the scientific literature for the description of manifold inhomogeneities and structural flaws in crystals, applied in optics, optoelectronics and the laser technics [55, 56].

In the specified operations convenient and blanket enough definition OA as any infringement of an optical indicatrix of a crystal is given. It is obvious, that in this definition by default it is supposed, that such infringements of an optical indicatrix of a crystal should be so essential that they could be found out observationally. In the same place classification OA by the characteristic sizes is offered also: OA macrolevel (more IOO a micron); OA mesolevel (10 microns-100 of a micron) and OA microlevel (less than 10 microns). Thus some structural flaws, for example, dislocations, not quite give in to reference in any of the numbered groups of the sizes. In many operations [57-60] with dislocations and their aggregations are related high (to 100 MPA) the mechanical voltages which display sometimes can be observed immediately owing to effect of a photoelasticity at an exposure to radiation of the transparent crystals. Therefore dislocations, as well as flaws of structure of other dimensionalities, it is necessary to carry to OA. However dislocations (except dislocation loops) penetrate crystals through, coming to an end on their surfaces, and often have the extents obviously exceeding 100 microns (macrolevel). At the same time it is formal in directions, orthogonal dislocation lines, its sizes do not exceed quantity of vector Bjurgersa, that is are close to lattice parametres - the order of 1 nanometer (microlevel). Except for dislocations, thus, all known structural flaws and optical inhomogeneities can be correctly carried to OA within the limits of offered in [55, 56] classifications.

C the purpose of giving to it still bolshej severity, followed include in list OA and a crystal surface, as it from the point of view of a crystallography and so concerns flaws of structure of the second order of dimensionality. And a role of surfaces in optical contortions of the light streams transiting through crystals, abundantly clear. In this connection and in the present operation in section 2.1. Influence of the shape of a microrelief (nanorelefa) surfaces of crystals on indicatrixes of a gear transmission and reflexion of light by crystals is specially viewed. C the account of it it is possible to number, as magnification of dimensionalities (orders) and the geometrical sizes, all structural both optical flaws and the inhomogeneities united by concept OA.

Nulmernye flaws and OA in crystals.

All nulmernye flaws - the impurity atoms, substitutional atoms, atoms of introduction, vacancy etc. - can be carried to flaws of microlevel. They, unconditionally, import the contribution in OA, and in OA all levels. For example, the active impurity atoms in semiconductor crystals spot types, concentrations and mobility of carriers of electricity and consequently their non-uniform allocation causes inhomogeneities of uptake and radiation dispersion in a material, being optical anomalies, and OA can be practically any sizes (levels). Besides, both in semiconductor, and in the dielectric crystals nulmernye flaws at certain concentrations can cause appreciable mechanical voltages, and, as consequence, to changes of an inductivity and the exponents of a refractive related to it Nevertheless, individual nulmernye flaws, first, are not resolved opticheski, and, secondly are not capable to cause major local infringements of an optical indicatrix of a crystal.

Therefore viewing separately OA, related with nulmernymi flaws of crystals, hardly probable defensible.

The one-dimensional (linear) flaws of structure and OA in crystals.

The major one-dimensional flaws of structure of the crystals, with OA dislocations are closely related. Dislocations, as is known, or penetrate all crystal and terminate in exit places on its surface, or become isolated on itself and form dislocation loops in a crystal [61]. In a direction along a dislocation these structural flaws are, unconditionally, flaws of macrolevel. In spite of the fact that in a transverse direction to a dislocation line its sizes are considered one after another equal to vector Bjurgersa, mechanical voltages near to a dislocation can reach several hundreds MPa and are spread to distances from several microns till 10-20 a micron [44]. Owing to pezoopticheskogo effect close even single dislocations essential changes of exponents of a refractive that was sometimes used for the purpose of optical detection of dislocations in silicon monocrystals in IK a gamut [57,62] are observed. Separate dislocations can be found out a method of X-ray topography [61], but their diffraction "images" do not give representation about optical anomalies caused by these flaws. Data on detection single dislocations in transparent in a visible gamut the dielectric crystals are available only in one operation [63] in which it is informed, that near to exits of poles of chemical etching on a surface of monocrystals paratellurita (TeO2) the bright polarisation contrast caused by localisation of mechanical voltages round dislocations (fig. 1.1) was observed.

In the massive polished samples of the transparent dielectric crystals at observations in transiting light separate dislocations are not resolved. However in operation [44] it is shown, that local-narrow and long - fields in crystals along which macroscopical quantity - the dislocation density - is raised in comparison with the next volumes
Material on 1-2 orders, in accuracy correspond protjazhyonnym to optical anomalies - sviljam.

Fig. 1.1. Polarisation contrast in the image of poles of chemical etching on a surface (110) monocrystals paratellurita, caused by mechanical voltages near to exits of dislocations [63]

Have twisted are the optical anomalies often enough meeting in glasses and monocrystals. Presence svilej in glasses is related, in the core, with formed as a result of infringements of technologies of glassmaking by heterogeneity of allocation of various impurities and special chemical additives. The origin svilej in the monocrystals gained from a melt, can have and other parents related not only with a chemical compound of initial substance and alloying additives, but, first of all, with temperature lapse rates in rostovoj to a band and with a kinetics spotted by them, and also with dislocation structure of a formed material.

The physical nature svilej in the glasses which are amorphous substances, and in crystals is various in connection with lack in the first the long-range order and flaws of structure, characteristic for crystals. That not
Less, owing to relatives by the form and on display of optical anomalies, terminology, methods of observation and metrology svilnosti (bessvilnosti), anchored in domestic gostah [64, 65] and in the international standards (ISO), are practically identical for svilej in glasses and in crystals. It is underlined, that have twisted garble optical images, in particular, have twisted in the form of stratums cause an astigmatism.

The elementary expedients of detection rough svilej in glasses and the crystals, consisting in examining (in a long-range band) through an explored optical device of any well shined subject having such shape in which there are flat surfaces or straight lines are known. At consecutive travel of an optical device concerning a beam of sight of the observer in those places where in a device are located have twisted, images of straight lines or subject planes are garbled, that allows to spot approximately localisation and quantity svilej in material volume. The specified expedient is suitable, certainly, only for rejection most svilnyh samples of glasses and monocrystals.

According to GOST 32361-2013. (The Glass and products from it. Defects), sviljami (cord, heavy cord, vein, striae) are termed sharply expressed local optical inhomogeneities. They represent the transparent threadlike or schistose inserts having an excellent exponent of a refractive from a great bulk of a material.

Observation method svilej and category definitions svilnosti (GOST 3521-81. A glass optical. A definition method bessvilnosti.) the collimator, and also the screen on which the beam of light transited through tested sample of a glass or a crystal and formativing the image svilej in a material is projected is grounded on use optical plans into which composition not laser light source (the ultraviolet valve DRSH) enters, the worlds, an objective with a diaphragm of variable diameter. The plan can be supplemented
The reference samples having a known category bessvilnosti - from І to IV.

As flaws of surfaces of tested samples also can lead to the strong contortions of images, the important requirement in metrology svilej is high quality of a polish of samples. The parametre of a roughness of surface Rz (a root-mean-square deviation of height of a lateral view) should not exceed 50 nanometers.

In standard documents of a category svilnosti are related to categories of optical homogeneity of materials, thus in the samples answering to the highest categories of homogeneity (I-II) have twisted should not be found out.

Fig. 1.2. Svil in a large-sized monocrystal paratellurita (it is scored

Arrow), observed in a bundle of laser dispersing light with a wave length of 533 nanometers on the remote screen

It is necessary to score, that methods of detection now in use and classification svilej, and also a numerical estimate bessvilnosti it is necessary to consider semiquantitative. Really, such parametres as number observed svilej, total length svilej and the area in the image of a site of the optical device, occupied are considered
sviljami. Not saying that at visual definition of these parametres always there is a subjective factor, their number does not include such important performance have twisted as the luminosity (contrast) of its image closely related to variations causing it of an exponent of a refractive. In one of gostov, norming svilnost, corresponding diversions of exponents of a refractive for those or other lengths of waves of radiation are not specified.

Besides the specified deficiencies, it is necessary to score, that the procedure of definition spread to crystals svilnosti glasses not always is correct and on a physical being. For example, in gostah in a material it is looked through in two is cross-orthogonal directions, and in case have twisted are not found out, the deduction about bessvilnosti a material becomes. Meanwhile in crystals really available have twisted can not be found out in any two orthogonal directions, but at device rotational displacement on some corner depending on a point group of symmetry of a crystal, become well visible in one or in both directions. Do not consider the procedures oriented on detection svilej in a glass, and such optical properties proper in many monocrystals, as two-refraction, an optical activity, a dichroism. In the present operation at examinations svilej and others OA in crystals the method of a conoscopy allowing not only to find optical inhomogeneities was applied, but also to count changes of exponents the refractives responsible for observable anomalies.

Proceeding from definition of the dimensional levels OA, data in operations [55, 56], it is necessary to carry them to optical anomalies of macrolevel, nevertheless, in concrete examinations meaning their small size in a transverse direction, concerning, more likely, to mesolevel.

Two-dimensional flaws of structure and OA in crystals.

Boundaries of blocks concern classical two-dimensional flaws of structure in crystals, MUG (malouglovye boundaries), and also a surface of a crystal [66].

Flaws of first two types, unconditionally, lead to optical anomalies, but they are not resolved as separate structural flaws by optical methods. In cases when light radiation impinges on a surface of such flaw, it is possible to fix only local distinctions in contortions of wavefronts on a surface of the block or MUT against the blanket contortion caused by two-dimensional flaw. In cases when observation is conducted along a flaw surface, OA can look as svil or a series svilej.

The surface of any crystal is not only purely geometrical two-dimensional flaw of structure. On it not only the correct transmitting alternation of atoms or molecules which is supposed in an ideal crystal is broken. As extreme atoms in the torn off chains have no neighbours from space where the crystal is not present, their electron couplings are not compensated, that leads to contortion of parametres of an ideal lattice, to occurrence of mechanical voltages, to inductivity change in pripoverhnostnom a stratum and, as consequence, to contortions in it of an optical indicatrix of a crystal. Thus, and from this point of view the crystal surface can be considered as OA. It is necessary to score, that this anomaly is spread on major enough - macroscopical distances deep into a crystal that is well visible on fig. 1. Z. Where the pattern on the screen in the long-range band, gained is presented at illumination by a plane-parallel bundle of laser light of a device from a crystal paratellurita in the form of a rectangular parallelepiped. Dark lines along lateral facets of the device, corresponding to order distances 2мм from facets, characterise boundaries pripoverhnostnyh stratums of a crystal with sharply changed exponents of a refractive.

Fig. 1.3. Dark lines along projections of facets of a device from a crystal

paratellurita, arisen owing to polarisation contrast on boundaries pripoverhnostnyh volumes with the changed exponents of a refractive

Unlike the two-dimensional flaws localised in volume of a crystal, the surface of an optical material can be in detail explored the advanced methods of raster-type electronic and atomno-power microscopy with the resolution to 1 nanometer, a method of the interference profilometrii - since 1 nanometer and to tens micron, and also by means of optical microscopy - since 1 micron and till the macroscopical sizes in hundreds micron and more.

At examinations of the polished crystals in transiting light flaws of structure of surfaces of macrolevel and mesolevel - scratches, flaws, "lasiny", "points" - are shown already as OA, they are projected on a plane of observation in the form of corresponding dark lines, stains and points, they are well appreciable and are easily fixed by photoequipment at various magnifications (fig. 1.4)

Fig. 1.4. Sproetsirovannoe on the remote screen the image of a plate,

Cut out from a crystal niobata lithium with the sizes 10x10x3 mm and shined kollimirovannym a bundle of laser light with a wave length

533 nanometers. Dark lines in the image - flaws of a polish on a surface of an input facet of a plate: lasiny, scratches, points

Flaws of surfaces of the microlevel, always present even on ideal to the up-to-date measures the polished surfaces, the sizes of unevennesses on which do not exceed 1-30 nanometers, in itself do not cause separate OA at least owing to them malosti in comparison with lengths of waves of visible radiation. However their cumulative activity, unconditionally, is shown in deterioration of integrated optical performances of a material - in reduction of a transmittance and in magnification of intensity of diffuse dispersion of light. And by detailed viewing of all flaws of the structure, veering distributions and intensity of the initial radiation flow impinging on a crystal, microscopic flaws of surfaces also should be considered [67, 68]. In II head of the present operation the computational method of total parametres of the light stream reflected, the past through a crystal, and also the material immersed in interior volumes, in which is presented
Are considered not only internal defects of structure and related C by them OA, but also thin structure of a microrelief of surfaces.

Volume (three-dimensional flaws of structure and related to them OA),

Any macroscopical and microscopic inserts of alien phases concern three-dimensional flaws of structure of a crystal. All of them to some extent garble an optical indicatrix of a crystal. Such alien inserts can be and impurities, but microscopic inserts of impurities are meant not as separate atoms, and large enough assotsiaty, thousand containing at least - hundred thousand the atoms forming in a crystal distinguishable demarcations with the basic phase. The observational detection of such individual inserts is difficult, not always a possible problem. However, as in the present operation were studied structural and optical flaws in crystals with obviously small impurity concentrations and other structural flaws (germanium, paratellurit), and requirements of cultivation of these crystals practically excluded occurrence in them of massive impurity inserts, was considered only integrated activity of microscopic inserts of impurities and nulmernyh the impurity flaws on optical indicatrixes of materials.

At the same time, sometimes meeting in crystals of the dielectrics which are grown up from a melt not in vacuo, vials with the sizes from several microns to several mm are simultaneously and three-dimensional flaws of structure, and rough enough OA [44]. According to with accepted in operations [55, 56] the classifications given OA can concern to

To macrolevel, mesolevel and microlevel.

In conclusion of the review of known types of structural flaws and optical anomalies corresponding to them it is necessary to score such well-known and observationally found out by the interference methods OA, as variations of exponents of a refractive. They are shown in the form of small fractures on lines of the interference maximums or
The minimums corresponding to an equal difference of a course of waves. An establishment of exact localisation of data OA in crystal volume, especially, methods of not destroying control, rather inconveniently. C the practical point of view it usually is not a problem as, consistently looking through all material through two crossly parallel planes polished on a crystal crystalline buli and having erected measure of an admissibility for heterogeneity of an exponent of a refractive (usually within 10 ' 4-10^5), it it is possible to choose and use at raskroe on devices volume of a crystal of comprehensible quality. In the present operation of a variation of an exponent of a refractive were found out at examination of crystals paratellurita and according to the author's procedures published in [69-71].

1.2.

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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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