RU2091824C1 - Optical materials - Google Patents

Abstract

FIELD: optical systems possessing an enhanced picture quality at theoretically critical characteristics. SUBSTANCE: for fabrication of lenses use is made of bismuth orto-germanate, which makes it possible to enhance the picture quality in development of optical systems at similar focal lengths due to correction of astigmatism because of the decrease of curvature of the refracting of the decrease of curvature of the refracting surface and increase the service life of optical systems due to nonhygroscopicity of the material, its monocrystallinity and high radiation resistance. EFFECT: enhanced picture quality. 1 dwg, 1 tbl

Description

The invention relates to optics, in particular to lenses, and can be used in optical systems having improved image quality with theoretically extreme characteristics. Optical glass materials with a high refractive index are known, in particular, super-heavy crowns CTK16 and CTK20 with refractive indices n _e = 1.790 and 1.768 and dispersions ν 45.4 and 50, respectively [1]
According to the chemical composition, superheavy crowns are borate glasses containing 7-39 mol. SiO ₂ ; 24-52 mol. B ₂ O ₃ ; 34-48 mol. (CaO, ZnO, Al ₂ O ₃ + La ₂ O ₃ , TiO ₂ , ZrO ₂ ) [2]
A group of heavy barite flints is also known [3], for example, TBP9 with n _e = 1.8129 and n 42.5, as well as TBP11 with n _e = 1.837 and n 42.8. The chemical composition of heavy barite flints consists of 20-40 mol. SiO ₂ ; 20 mol. B ₂ O ₃ ; 3-43 mol. BaO, PbO with additives of ZnO, CaO, TiO ₂ , WO ₃ [2]
These glasses are quite promising for improving image quality in the development of optical systems with characteristics close to the limit. However, the refractive index of these glasses is limited by the values indicated above, and cannot be more than 2.0, while they have high dispersion values.

 A rather complicated manufacturing technology of such glasses of optical quality limits their production and determines a high cost.

In addition to the disadvantages of these glasses is their interaction with moisture. In terms of spotability, glass containing> 17 mol. B ₂ O ₃ belong to group III (stained glass) and group IV (unstable glass) [4]
Closest to the proposed material for the manufacture of lenses is optical material: which includes a group of superheavy flints [5] of type STF2 with n _e = 1.955, and n 20.2 and STF3 with n _e = 2.186 and n 16.6. In terms of chemical composition, super-heavy flints consist of 50 mol. SiO ₂ ; 48-59 mol. PbO and 0.5-1.5 mol. K ₂ O (Na ₂ O).

The disadvantage of such glasses is a yellow tint, which reduces transparency in the visible region by 10-20% and also increased crystallization ability, which leads to a change in optical characteristics due to aging [4]
The technical result of the invention is the search for optical refractive material with a high refractive index [1, 2] with a relatively low dispersion (n 20), which provides improved image quality.

According to the invention, the technical result is achieved due to the fact that the bismuth orthogermanate Bi ₄ Ge ₃ O ₁₂ , the refractive index of which is n = 2.1, and the dispersion is n 20.

 The specified compound is described in the literature [6] and was previously used as scintillation material for recording gamma radiation, electron, and other elementary particles in nuclear physics, geology, and medicine. The use of bismuth orthogermanate for the manufacture of lenses is not described in the literature.

The use of Bi ₄ Ge ₃ O ₁₂ bismuth orthogermanate in comparison with ordinary crown and flint glasses (analogues and prototype) at the same (normalized) focal lengths leads to less curvature of the refracting surfaces and, as a result, to a decrease in aberrations of all orders, and this, in turn, leads to the possibility of increasing the relative aperture of the optical system without complicating it. At the same time, in addition to the possibility of creating new systems, it becomes possible to simplify commercially available optical systems, in particular, photo lenses by replacing complex corrective-power components with simpler ones containing bismuth orthogermanate.

Thus, the use of Bi ₄ Ge ₃ O ₁₂ as an optical material in the manufacture of lenses of optical systems makes it possible to improve image quality without complicating them by reducing the curvature of the refracting surface and by correcting astigmatism.

 Obtaining single crystals of bismuth orthogermanate.

The initial mixture of bismuth (III) oxides grade OSF 13-3 (for single crystals) and germanium oxide (IV) (TU 48-21-72), taken in the ratio of Bi ₂ O ₃ : GeO ₂ 2: 3, in an amount of 1.0 kg is mixed in an agate mortar and then solid-phase synthesis of the Bi ₄ Ge ₃ O ₁₂ mixture is carried out in a platinum cup in air at 750-950 ^o C. The resulting mixture is loaded into a platinum crucible with a diameter of 200 mm, a height of 300 mm in the amount of 40 kg, melted and carried out the process of growing single crystals by the Czochralski method for oriented seed. Colorless single crystals with a diameter of up to 150 mm and a length of up to 250 mm are obtained.

 The drawing shows an eyepiece.

 An example of a specific use is the development of an eyepiece for telescopic systems. The eyepiece has the following design parameters (see table).

в пределах поля ω 30^o не превышает 2 мм, что более чем в три раза лучше, чем в известном окуляре).The calculation of the actual ray path indicates that, compared with the well-known three-lens eyepiece, in which one lens (N 1) with a high refractive index (n = 2.0667) made of superheavy flint [7] is replaced by a bismuth orthogermanate lens, this eyepiece has improved image quality by reducing the curvature of the lens surface, and correcting astigmatism (astigmatic difference

within the field ω 30 ^o does not exceed 2 mm, which is more than three times better than in the known eyepiece).

The use of lenses made of Bi ₄ Ge ₃ O ₁₂ bismuth orthogermanate in the development of optical systems with the same (normalized) characteristics allows improving image quality without complicating the optical system, as well as significantly expanding the spectral range of application of optical devices.

In addition, the use of Bi ₄ Ge ₃ O _{12 is} economically advantageous, since allows to reduce the cost of products due to the simple manufacturing technology of the proposed optical material.

 The use of lenses made of bismuth orthogermanate also allows to increase the life of optical systems due to the non-hygroscopic nature of the material used (lack of spotting), and high radiation resistance.

 Since a single crystal is used as an optical material (rather than glass as in the prototype), one of the main disadvantages of highly refracting glasses, namely, increased crystallization ability, is eliminated, which also allows to increase the life of this material.

Information sources:
1. Colorless optical glass of the USSR. Catalog. M. Gosstandart, 1990, p. 52.

 2. Physico-chemical fundamentals of the production of optical glass / ed. L. I. Demkina. L. Chemistry, 1976, p. 62-77.

 3. Colorless optical glass of the USSR. Catalog. M. Gosstandart, 1990, p. 62.

 4. Physico-chemical principles of the production of optical glass / ed. L. I. Demkina. L. Chemistry, 1976, p. 185-186, p. 209-220.

 5. Colorless optical glass of the USSR. Catalog. M. Gosstandart, 1990, p. 74.

6. Kargin Yu.F. Kargin V.F. Skorikov V.M. Shadeev N.I. Pekhova T.I. Synthesis and emission of scintillation properties of Bi ₄ Ge ₃ O ₁₂ single crystals. Izv. USSR Academy of Sciences, Inorganic Materials, 1984, v. 20, No. 5, p. 815-817.

 7. Rusinov M.M. Composition of optical systems. L. Mechanical Engineering, 1989, p. 202-203.

Claims (1)

The use of single crystals of bismuth orthogermanate Bi ₄ Ge ₃ O _{1 2} in optical systems as an optical material with a refractive index of n 2.1 and a dispersion of ν = 20.n

Images