Optical glass with convex-concave surfaces: manufacturing, application. Lens, magnifying glass

Optical glass is a specially made transparent glass, which is used as parts for optical instruments. It differs from the usual cleanliness and increased transparency, uniformity and colorlessness. Also, dispersion and refractive power are strictly standardized in it. Compliance with such requirements increases the complexity and cost of production.

History

You can find many examples of everyday use of lenses, for example, a magnifying glass - an ordinary magnifying glass - will help create a small projector from an ordinary smartphone, but optical glasses have appeared not so long ago.

Lenses have been known since antiquity, but the first serious attempt to create glass, similar to what is used in modern instruments, can be attributed to the XVII century. Thus, the German chemist Kunkel in one of his works mentioned the phosphoric and boric acids that make up the glass component. He also spoke about borosilicate crown, which is close to some modern materials on the composition. This can be called the first successful experience in the production of glass, which has certain optical properties and a sufficient degree of physical and chemical uniformity.

In industry

The manufacture of optical glasses on an industrial scale began in the early 19th century. Swiss Gian, together with Fraunhofer, introduced a relatively stable method of obtaining such glass at a plant in Bavaria. The key to success was the reception of melt mixing by circular motions of a clay rod vertically immersed in glass. As a result, it was possible to obtain an optical glass of satisfactory quality, with a diameter of up to 250 mm.

Modern production

In the production of color optical glasses additives with substances containing copper, selenium, gold, silver and other metals are used. Cooking takes place from the charge. It is loaded into refractory pots, which, in turn, are placed in a glass furnace. The composition of the charge can include up to 40% of waste glass, an important point is the consistency of the cullet composition and the brewing glass. Glassmass during the cooking is continuously mixed with a ceramic or platinum blade. Thus, a homogeneous state is achieved.

Periodically, the melt is taken on a sample, which controls the quality. An important stage of cooking is clarification: in the glass mass of the clarifying substances originally added to the mixture, a significant amount of gases is released. Large bubbles form which quickly rise, capturing smaller bubbles that inevitably form during cooking.

Finally, the pots are removed from the oven, after which they slowly cool down. Cooling, delayed by special methods, can last up to eight days. It must be uniform, otherwise in the mass may be formed mechanical stresses that cause cracks.

Properties

Optical glass is a material for the production of lenses. They, in turn, are divided in appearance into collecting and scattering. Collectors include a biconvex and a flat-convex lens, as well as a concave-convex lens, called the "positive meniscus."

Optical glass has a number of characteristics:

• The refractive index, determined by two spectral lines, which are called the sodium doublet;
• Mean dispersion, by which is meant the difference in refraction of the red and blue lines of the spectrum;
• Coefficient of dispersion - the number given by the ratio of mean dispersion and refraction.

Color optical glass is used to produce absorption filters. Depending on the material, three main types of optical glasses are distinguished:

• Inorganic;
• Plexiglass (organic);
• Mineral-organic.

The composition of inorganic glass includes oxides and fluorides. Quartz optical glass also refers to inorganic (chemical formula SiO ₂ ). Quartz has a slight refraction and a high light transmittance, it is characterized by heat resistance. A wide range of transparency makes it possible to use it in modern telecommunications (fiber optic cables and so on), also silicate glass is indispensable in the manufacture of optical lenses, for example, quartz is made by magnifying glass.

Based on silicon

Transparent silicate glass can be both optical and technical. Optical is made by melting rock crystal, this is the only way to get a completely homogeneous structure. In opaque glasses, small bubbles of gas inside the material respond to the color.

In addition to quartz glass based on silicon, the so-called silicon glass is produced, which, despite its similar base, has other optical properties. Silicon elements are capable of refracting X-rays and passing infrared radiation.

Organic glass

The so-called plexiglass is made on the basis of a synthetic polymer material. This transparent and hard material refers to thermoplastics and is often used as a replacement for quartz glass. Plexiglas is resistant to many environmental factors, such as high humidity and low temperatures, but it is much softer, and therefore more sensitive to mechanical effects. Because of its softness, organic optical glass is easy to process - it can be "taken" even by the simplest tool for cutting metal.

This material is excellent for laser processing, it is easy to apply a pattern or engraving. As a lens, it perfectly reflects infrared rays, but misses ultraviolet and X-rays.

Application

Optical glasses are widely used for the manufacture of lenses, which, in turn, are used in many optical systems. A single collecting lens is used as a magnifying glass. In technology, lenses are an important or major part of systems such as binoculars, optical sights, microscopes, theodolites, telescopes, as well as cameras and video equipment.

No less important are optical glasses for the needs of ophthalmology, because without them it is difficult or impossible to correct visual defects (nearsightedness, astigmatism, hyperopia, disruption of accommodation and other diseases). Lenses for glasses with diopters can be made both from quartz glass, and from high-quality plastic.

Astronomy

Optical glasses are an important and most expensive component of any telescope. Many fans themselves collect refractors, this requires little, but most importantly - a flat-bulb glass lens.

At the beginning of the century before last, it took several years to produce one powerful astronomical lens, or rather, to polish it. For example, in 1982, the head of the University of Chicago William Harper addressed the millionaire Charles Yerkes with a request to finance the observatory. Yerkes invested about three hundred thousand dollars in it, and forty thousand went to buy a lens for the most powerful telescope at that time on the planet. The observatory was named in honor of the financier Yerkes, and so far this refractor with a lens diameter of 102 cm is considered to be the largest in the world.

Telescopes with a large diameter are reflectors, in it a mirror is a light-gathering element.

There is another type of lens used in astronomy and in ophthalmology - a glass with convex-concave surfaces called meniscus. It can be of two types: scattering and collecting. In the dissecting meniscus, the extreme part is thicker than the central, and in the collecting more thin is the central part.