RU2398921C1 - Method of growing kdp group monocrystals on nucleating agent placed in mould - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: method is realised by growing group KDP monocrystals for linear optical elements on a rectangular nucleating agent of the corresponding KDP group monocrystal. A Z-cut nucleating agent 2 is used, whose size in the [100] direction is determined by one of the smaller sizes (b) of the aperture of the rectangular nonlinear optical element, and its length (L) in the [010] direction is equal to the sum of the projections of the height (c) and second (a) larger value of the aperture of the nonlinear optical element on plane (001) and is described the following formula: L=cSinc+aCosc, where c is angle of synchronism characteristic for each KDP group crystal. The nucleating agent is placed inside a dismountable mould in form of a closed frame assembled from separate boards, each of which is fitted in the following sequence: nucleating agent 2 is placed on the board of the base 1 of the mould, board 3 is then placed vertical to the said board and another board 5 is fitted at an angle of synchronism c, the next board 6 is placed at an angle of 90 to the previous board 5 and the closing board 7 is placed perpendicular to the board of the base 1 of the mould which gives the given shape and size of the grown monocrystal in form of a workpiece. ^ EFFECT: invention enables to move way from the conventional technological process, when during free arrangement of a nucleating agent in the reaction volume of a crystalliser, a crystal with habit which is natural for the given substance is obtained, to a technological process which enables to directly obtain a monocrystal workpiece with given size and shape during the growing process for making optical elements. ^ 1 ex, 1 tbl, 5 dwg

Description

The invention relates to methods for producing oriented single crystals used in laser physics, acoustoelectronics, optoelectronics.

The KDP group includes single crystals of alkaline ion dihydrogen phosphates (KH ₂ PO ₄ , RbH ₂ PO ₄ , etc.) and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ). Single crystals of the KDP group are among the most important single crystals that are used in nonlinear optics devices [A. Blistanov Crystals of quantum and nonlinear optics. - M. MISiS, 2000. - 432 p.].

The invention allows us to move from the traditional technological process when, when the seeds are placed freely in the reaction volume of the crystallizer, a crystal with a habit that is natural for a given substance is obtained, to a technological process that allows producing an economical single crystal workpiece directly in the process of growing, close in size, shape and orientation to manufactured optical element.

Numerous publications describe and apply in practice a very significant number of methods and technologies for growing KDP group single crystals, which make it possible to obtain perfect single crystals. All these technologies are based on the well-known traditional methods of growing single crystals from aqueous solutions. This is a method for growing water-soluble single crystals by isothermal evaporation of a solvent and a method for growing single crystals when a mother liquor is cooled (Crystal growth from solutions. / TG Petrov, E.B. Treyvus, Yu.O. Punin, A.P. Kasatkin. - L .: Nedra, 1983.- 200 p.).

For crystals of the KDP group grown by traditional methods, natural faceting is a combination of two simple forms: a tetragonal prism {100} and a tetragonal dipyramid {110}.

In the manufacture of optical elements from single crystals with such a facet, the efficiency of using their volume is very low. This is due to the fact that optical elements must be made from the most perfect part of a single crystal. A number of consecutive technological operations for the manufacture of an optical element from a crystal (imparting the necessary shape, orientation, size, grinding, etc.) lead to the fact that a significant part of it goes to waste. The waste zone inevitably leaves the single crystal seed regeneration zone and an equal part of the crystal with a maximum concentration of dislocation and uncontrolled microimpurities. As a rule, tetragonal pyramids and a significant part of its main volume, the tetragonal prism, which also closes the grown single crystal, also go to waste. most of the long-growing and expensive crystal goes to waste.

Especially uneconomical are the volumes of KDP group single crystals grown in the manufacture of optical elements for laser frequency converters. This is due to the fact that the blank of the optical element - a rectangular parallelepiped - must also be inscribed in the most perfect part of the single crystal, and this blank must be located at the synchronism angle corresponding to the single crystal (Gurzadyan G.G., Dmitriev V.G., Nikogosyan D. N. Nonlinear optical crystals. Reference book. - M.: Radio and communications, 1991. - 160 p.) To its direction [001], i.e. in the manufacture of a nonlinear optical element from a single crystal grown by these methods, initially it is necessary by mechanical methods (cutting, grinding, etc.) to create a base plane oriented (by X-ray methods) with respect to the [001] direction at the angle of synchronism. Further consecutive technological operations, allowing to obtain a rectangular billet of the optical element, lead to the fact that in this case, most of the single crystal also goes to waste.

Thus, the natural faceting of KDP group single crystals grown from a solution is an obstacle to creating a more economical and efficient technology in the manufacture of optical elements and, in particular, nonlinear optical elements.

The inability to manufacture an optical element without sending a significant part of the single crystal to waste is a fundamental feature of the KDP group single crystals grown by traditional methods.

Closest to the proposed method is a method of growing single crystals of the KDP group (SU 00000955741, IPC С30В 7/02, 29/14, 04/10/1996). The main objective of this method is to increase the growth rate and optical uniformity of crystals. This is achieved, first of all, by choosing the crystallographic orientation of the seed relative to the faces of the prism (100) or the faces of the pyramid (101) and choosing the optimal supercooling of the mother liquor for these cases, which ultimately ensures the achievement of the goal. The placement of the seed at the bottom of the mold precisely in size without a gap and at the same time at an angle in the range of 45-90 °, although it allows to obtain a crystal oriented at an angle of synchronism with respect to the [001] direction, is rather a serious drawback. With this placement of the seed, the likelihood of internal mechanical stresses is very high, since all four side faces of the growing crystal are bounded by the walls of the mold. The possibility of destruction of a single crystal with internal mechanical stresses when removed from the mold or during subsequent machining is almost inevitable.

The purpose of the proposed method for growing single crystals of the KDP group is to obtain a single crystal billet for the manufacture of several optical elements oriented at an angle of synchronism with the required dimensions and the absence of internal mechanical stresses that may arise during its growth.

The technical result of the invention is to create conditions that allow to grow a single crystal billet, in its size and shape as close as possible in size and shape to the optical elements made from it. Moreover, in order to prevent mechanical stresses in the growth of the single crystal during the growth process, the mother liquor washes the maximum possible number of freely growing crystal faces.

This method is ensured by the fact that the KDP group single crystals are grown for nonlinear optical elements by the rectangular seed of the corresponding single crystal and characterized in that they use the Z-cut seed, the size of which in the [100] direction is determined by one of the smaller sizes (b) of the aperture of a rectangular nonlinear optical element, and its length (L) in the direction [010] is equal to the sum of the projections of the height (s) and the second (a) larger aperture of the nonlinear optical element on the (001) plane and is described by the following form muloy:

L = cSinθ _c + aCosθ _c , where θ _c is the phase angle, characteristic for each of the crystals of the KDP group. The seed is placed inside a demountable shaper in the form of a closed frame assembled from individual slats, each of which is installed in the following sequence:

on the base plate of the former place the seed,

vertically specified strip set the next strip,

then relative to it at a synchronism angle θ _c set another bar,

the subsequent strip relative to the previous strip is placed at an angle of 90 °,

the closing strip is installed perpendicular to the base strip of the former, which provides the desired shape and dimensions of the grown single crystal in the form of a workpiece.

The invention is illustrated by drawings, which show the basic elements and stages of installation of the former, which allows to provide the necessary technical result. Several possible sequentially complicated and sequentially more efficient assembly options of the former are considered (FIGS. 2-5).

The first is the basic version (Figure 2):

- flat seed 2, made of a Z-cut single crystal, with dimensions determined by the above principle, is placed on the base plate 1 of the assembled shaper. The size and shape of the base correspond to the shape and size of the seed. The strap 3 is installed vertically relative to the base of the former on one of its smaller ends. The length of this bar is determined by the height of the defective part of the single crystal 4 (region of the regeneration zone), which subsequently goes to waste, plus the value determined by the ratio aSinθ _c . The next strip 5 relative to the previous one is installed at an angle of synchronism θ _c , which is characteristic of this single crystal. Its length is equal to the height of the optical element (s). The resulting internal angle of the former is 180 ° - θ _s . Plank 6 relative to the previous one is installed at an angle of 90 °. Its length is equal to the larger side (a) of the aperture of the optical element. The closing shaper strip 7 will be perpendicular to the base of the shaper and, accordingly, to the second opposite end face of the seed.

. Такая конструкция формообразователя позволяет получить технологичный и экономичный по форме монокристалл-заготовку для дальнейшего использования. Заготовка имеет готовую базовую плоскость под заданным углом синхронизма относительно направления [001] и три перпендикулярные к ней плоскости нелинейного оптического элемента. Завершается изготовление прямоугольного нелинейного оптического элемента механическим удалением неиспользуемых частей выращенного монокристалла - Г, Д и Е.In this case, the seed expands either in the direction [001] or in the direction

. This design of the former allows you to get technological and economical in shape of a single crystal blank for further use. The workpiece has a finished base plane at a given angle of synchronism with respect to the [001] direction and three planes of a nonlinear optical element perpendicular to it. The manufacturing of a rectangular nonlinear optical element is completed by mechanical removal of the unused parts of the grown single crystal - G, D and E.

The following three assembly options for the formers, schematically shown in FIGS. 3, 4 and 5, are obtained by mirror reflection (mirror symmetry) relative to the axes A-A or B-B (FIG. 2). In this case, of course, instead of the internal base strips, a seed is installed.

The second option (Figure 3).

(в отличии, например, от гексагонального иодата лития, у которого анизотропия скоростей роста в этих направлениях весьма ярко выражена, и такого разращивания, как правило, не производят). В этом случае конструкция формообразователя должна обеспечивать возможность расти кристаллу в вышеуказанных направлениях одновременно. Эти условия можно обеспечить, если при создании формообразователя использовать зеркальное отражение относительно оси Б-Б (Фиг.2). Разращивание затравки в таком формообразователе позволяет получить экономичный монокристалл, из которого можно получить уже две заготовки для изготовления нелинейных оптических элементов.Quite often, KDP group single crystals are grown simultaneously in the [001] direction and in the direction

(unlike, for example, hexagonal lithium iodate, in which the anisotropy of the growth rates in these directions is very pronounced, and, as a rule, they do not produce such growth). In this case, the design of the former should provide the ability to grow the crystal in the above directions simultaneously. These conditions can be achieved if, when creating the former, mirror reflection relative to the BB axis is used (FIG. 2). The growth of the seed in such a shaper allows you to get an economical single crystal, from which you can already get two blanks for the manufacture of nonlinear optical elements.

And with this option, the dimensions of a flat rectangular elongated seed in the [100] direction are calculated according to the above principle.

The third option (Figure 4).

Double the length L of the seed, calculated in accordance with the above principle, use mirror reflection relative to the axis AA (Figure 2) and obtain the following design of the former. The growth of the seed in this former also allows you to get an economical single crystal, from which you can get two blanks for the manufacture of nonlinear optical elements.

The fourth option (Figure 5).

Double the length of the seed and simultaneous mirror reflection relative to the axes aa and bb allows you to get the fourth configuration of the former. From a single crystal grown in such a shaper, it is possible to make four blanks for nonlinear optical elements, which are similar to the optical blanks obtained when using the shaper according to the first embodiment.

In all cases, the width of the forming strips should be slightly larger than the calculated thickness of the grown single crystal in order to prevent their ingrowth into the single crystal.

Compared with crystals obtained by traditional methods, the described method of growing single crystals of the KDP group provides significant advantages when using these crystals for the manufacture of optical elements:

- convenient technological form of the grown single crystals, excluding a number of labor-intensive technological operations in the manufacture of optical elements;

- the ability to get directly in the process of growing oriented economical single-crystal blank of a nonlinear optical element;

- high efficiency of using the volume of a single crystal, i.e. a significant reduction in the amount of waste in the manufacture of optical elements for converting laser radiation;

- high efficiency of the actual process of growing single crystals of the KDP group. In a standard mold, you can place several formers that are assembled on one holder, providing a uniform flow of the mother liquor to the growing faces during the reverse rotation of the entire system, i.e. to grow several single crystals in one cycle from one volume of the mother liquor.

The method is illustrated by the following example.

Example.

Five KDP single crystals (KH ₂ PO ₄ ) were grown in one crystallizer. One without the use of a shaper on a traditional rectangular seed and four on the seeds calculated according to the above principle with the use of shapers in accordance with the four above-described options. All single crystals are grown by the traditional method of programmed cooling of the mother liquor. The dimensions of the seeds and the sizes of the former are selected so that from the perfect part of each of the single crystals it was possible to make only one blank for an optical element of the same size. In this case, minimum sizes of single crystals were provided for the same size of optical elements. This made it possible to compare the efficiency of using the volume of grown single crystals and analyze their technological features — the presence and quantity of oriented planes (faces) that do not require preliminary technological processing. The use of a shaper made it possible to increase the efficiency of using the volume of a single crystal to 34% compared to 11% for a single crystal grown in the traditional way. Data for comparative analysis are shown in table 1.

All crystals had the structure of the seed regeneration zone typical for KDP crystals and equal in height to the characteristic zone with a high dislocation content, which, according to preliminary calculations, did not fall into the volume of the fabricated optical element blanks. It should be noted that the height of the regeneration zone for crystals grown on seeds elongated in the [010] direction was much smaller and equal to half the seed width.

The areas of crystals located in the immediate vicinity of the bounding strips of the former, did not have visible defects — cracks and trapped mother liquor. Control of internal mechanical stresses by measuring abnormal biaxiality showed their practical absence. The outer surfaces of single crystals, which during the growth process touched the strips of the former, were shiny smooth and did not have protrusions and shells on the surface.

Table 1 KDP single crystal (KH ₂ PO ₄ ) The volume of the crystal (mm ³ ) V _to Volume of element (s) (mm ³ ) V _el Number of elements (pcs.) Effect. used crystal volume V _eff = V _el / V _k · 100% Number of finished faces for element (s) Without shaper (prototype) 18163 2000 one eleven% - With Shaper Option 1 5859 2000 one 34% four With Shaper Option 2 11718 4000 2 34% 8 With Shaper Option 3 11718 4000 2 34% 8 With Shaper Option 4 23436 8000 four 34% 16

Claims (1)

A method of growing single crystals of the KDP group for nonlinear optical elements onto a rectangular seed of the corresponding single crystal from the KDP group, characterized in that they use a Z-cut seed, the size of which in the [100] direction is determined by one of the smaller sizes (b) of the aperture of the rectangular nonlinear optical element, and its length (L) in the direction [010] is equal to the sum of the projections of the height (s) and the second (a) larger aperture of the nonlinear optical element on the (001) plane and is described by the following formula: L = csinθ _c + acosθ _c , where θ _c - at Synchronicity characteristic of each of the crystals of the KDP group, place it inside the detachable shaper in the form of a closed frame assembled from separate strips, each of which is installed in the following sequence: a seed is placed on the base of the shaper, the next strip is installed vertically, then the next it at an angle θ _c synchronism establish another bar, the bar relative to a previous subsequent placed at 90 °, the closing bar mounted perpen ikulyarno strip shaper base that provides a predetermined shape and dimensions of a single crystal grown in a workpiece.

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