Optical glass

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The Abbe diagram gives an overview of the refractive index and Abbe number of optical glass types.

Under optical glass is meant glass for the manufacture of optical components (such as lenses , prisms and mirrors ) for optical systems such as lenses , microscopes or telescopes . Optical glass does not necessarily differ chemically from normal glass, from which window panes are made, but its optical properties are precisely adjusted through targeted chemical additives. The optical and mechanical properties are also precisely checked and documented by the manufacturers.

Optical and physicochemical properties

The optical properties, which are of crucial importance for the use of the glass for optical components, are maintained within narrow tolerances during the manufacture of the glass and are controlled much more precisely than z. B. with window glass. Furthermore, they are precisely documented by the manufacturer for each type of glass. These include:

  • The refractive index and its dependence on the wavelength of the light ( dispersion ). The latter is mainly characterized by the Abbe number . Partial dispersions and often the coefficients of a dispersion formula such as the Sellmeier or Cauchy equation are given for a more precise description of the dispersion .
  • Deviations from the homogeneity of the glass, such as streaks (ribbon- like short-range fluctuations in the refractive index within a glass component in the range from 0.1 mm to 2 mm) or the content of bubbles and other inclusions.
  • Properties that are important for the production of optical components and their behavior in use, such as sandability, thermal expansion , changes in the refractive index with temperature or sensitivity to chemical influences ( glass corrosion ).

Types and names of optical glasses

Dependence of the refractive index on the wavelength for some types of optical glass.

There are over 250 optical glasses today. They are mainly based on the two most important glass families Kronglas K (English crown ) and Flintglas F (English flint ). In addition, in the name of Schott glasses have with the addition S for "heavy" (eng. Dense ), a high refractive index and L for "light" (eng. Light display), a low refractive index as heavy flint glass SF6 (eg., Or Light flint glass LF5). Additional chemical components that are decisive for the optical properties are placed in front of the main types of glass in the designation (e.g. barium crown glass N- Ba K4 or S- BA L14 or fluorine crown glass F K). Environmentally friendly arsenic and lead-free glasses are also marked with N- (e.g. N-BK7) at Schott and S- with Ohara (e.g. S-BSL7). Exceptions are glasses that are sold under their brand names , such as the glass-ceramic material Zerodur .

Examples of some types of optical glass from different manufacturers
(refractive index n d at 587.6 nm)
Glass type Schott AG Hoya KK Corning Inc. Ohara Inc. Density
in g / cm³		 n d
Quartz glass 2.20 1.46 68
Fluorine crown glass N-FK51A 3.68 1.49 85
Crown glass N-K5 C5 S-NSL5 2.59 1.52 60
Borosilicate crown glass N-BK7 BSC7 BSC B16-64 S-BSL7 2.51 1.52 64
ZERODUR® 2.53 1.54
Barium crown glass N-BaK4 BaC4 S-BAL14 3.05 1.57 56
Light flint glass LF5 FL5 3.22 1.58 41
Heavy crown glass N-SK4 BaCD4 S-BSM4 3.54 1.61 59
Flint glass F2 F2 3.60 1.62 36
Heavy flint glass N-SF10 E-FD10 FeD D28-28 S-TIH10 3.05 1.73 29
Heavy flint glass SF6 FD6 FeD E05-25 5.18 1.81 25th
Heavy flint glass N-SF6 FD60 S-TIH6 3.37 1.81 25th
Lanthanum heavy flint glass N-LaSF9 TaFD9 S-LAH71 4.41 1.85 32

Chemical composition and transmission range

The following table shows the chemical composition in percent by weight and the transmission range of some important types of optical glass. The transmission ranges are approximate and vary slightly in the sub-glass types. The transmission also depends on the glass thickness.

Glass type SiO 2 Al 2 O 3 Na 2 O K 2 O CaO P 2 O 5 B 2 O 3 PbO BaO Li 2 O TiO 2 ZrO 2 ZnO MgO Nb 2 O 5 Transmission range
Quartz glass 100 200 ... 3000 nm
Borosilicate glass 80 3 4th 0.5 12.5 350 ... 2000 nm
Crown glass (K) 73 2 5 17th 3 350 ... 2000 nm
Borosilicate crown glass (BK7) 70 8.4 8.4 10 2.5 350 ... 2300 nm
Flint glass (F) 62 6th 8th 24 400 ... 2500 nm
ZERODUR® 55.4 25.4 0.2 0.6 7.2 3.7 2.3 1.8 1.6 1 400 ... 2700 nm
Heavy flint glass (SF6) 27.3 1.5 71 380 ... 2500 nm
Heavy flint glass (N-SF6 / S-TIH6) 25th 10 10 10 10 25th 1 5 400 ... 2000 nm

Combination of optical glasses

The glass manufacturers offer a wide range of types of glass with different refraction and dispersion properties. The more glasses a designer can choose from, which he can combine in an optical system (e.g. an objective ), the easier it is to correct the aberrations .

For example, by using two glasses with different Abbe numbers, an achromatic objective can be realized whose chromatic aberration (color error) is largely corrected. The remainder of the chromatic aberration is called the secondary spectrum . With three different glasses, of which at least one is a glass of anomalous dispersion , an apochromat can be built in which the secondary spectrum has also been eliminated and which has practically no color errors.

  • Effect of the different dispersion behavior of crown glass and flint glass using the example of converging lenses .

  • Combination of crown glass and flint glass in an achromatic lens to correct chromatic aberration .

  • Elimination of the secondary spectrum in an apochromat by using several types of optical glass.

In addition, for the correction of non-chromatic aberrations, it is helpful to have glasses with various combinations of refractive index and Abbe number, especially so - called high - refractive glasses , which have a high refractive index with a high Abbe number.

literature

  • Hans Bach, Norbert Neuroth: The Properties of Optical Glass. 2nd Edition. Springer, 1995, ISBN 3-540-58357-2 .
  • Jai Singh: Optical Properties of Condensed Matter and Applications. John Wiley & Sons, 2006, ISBN 0-470-02192-6 , pp. 159-196 ( Chapter 8 - Optical Properties of Glasses. ).
  • George H. Steward: Optical Design of Microscopes (SPIE Tutorial Texts). SPIE Press, 2010, ISBN 978-0-8194-8095-8 , pp. 169-194 ( Chapter 17/18 - Optical Materials / Composition and Spectra of Materials. ).

Web links

Individual evidence

  1. ↑ Ralf Jedamzik, Peter Hartmann: Homogeneity of optical glasses. (PDF) In: DGaO-Proceedings. 2004
  2. ^ A b Hans Bach, Norbert Neuroth: The Properties of Optical Glass . Springer, 1995, ISBN 978-3-540-58357-8 , pp. 39-76 .
  3. ↑ Optical Glass Data Sheets . Schott AG, 2011; Retrieved October 1, 2012.
  4. ↑ Optical glasses - technical information . (PDF; 652 kB) OHARA GmbH, 2010; Retrieved November 8, 2011.
  5. ↑ a b D. Heiman, DS Hamilton, RW Hellwarth: Brillouin scattering measurements on optical glasses. In: Physical Review B (Condensed Matter). Volume 19, Issue 12, 1979, pp. 6583–6592, phys.uconn.edu (PDF)
  6. ↑ Michael J. Viens: Fracture Toughness and Crack Growth of Zerodur. In: NASA Technical Memorandum 4185 April 1990, ntrs.nasa.gov (PDF)
  7. ^ George H. Steward: Optical Design of Microscopes (SPIE Tutorial Texts). SPIE Press, 2010, ISBN 978-0-8194-8095-8 , p. 194 ( Chapter 18 - Composition and Spectra of Materials. )