Goodfellow Catalogue OPTICAL GLASSES

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OPTICAL GLASSES When a ceramic microstructure is entirely glassy, non-crystalline and amorphous, the material is defined as glass.

Glass is composed mainly of sand (silicates, SiO2) and possibly an alkali metal. Optical glasses are fabricated by mixing a number of purified compounds in the form of a powder, heating them to produce a glass melt, and slowly cooling them until the optimum solidification is achieved.

Characteristics of Glass

Due to its amorphous structure, glass has the ability to refract, reflect, and transmit light without scattering it, demonstrating a certain refractive index and transmission range. Depending on the final use and application, the composition of the glass and the cooling rate will vary. Other metal elements and oxides can be added to increase properties such as thermal and chemical durability or absorption of light in different wavelengths (e.g. infrared or ultraviolet). General characteristics of glass are shown below:

> Transparent or translucent > Hard and brittle > Heat resistant > Impact and breakage resistant > Electrical and electromagnetic resistivity > Chemically non-reactive

Examples of Optical Glasses

Based on the composition, different types of optical glasses can be produced. Examples include: > N-BK7 glass, a Borosilicate glass > B270, a colourless clear Crown glass (Alkali-lime Silicates containing approximately 10% Potassium Oxide) > Corning Eagle 2000 XG, an Alkaline Earth Boro-Aluminosilicate glass > Quartz (crystalline Silica) and Fused Silica (non-crystalline Silica) > Synthetic Sapphire glass (single crystal Alumina) > Zerodur, a Lithium-Aluminosilicate glass-ceramic > Potassium Aluminosilicate > Filter glasses

Depending on the material, standard sizes start from 0.025mm thick and lengths of 2mm.

In addition, in order maximise performance for applications operating above 700nm wavelengths – including thermal imaging, FLIR or spectroscopy – infrared (IR) glasses are used. These glasses include Germanium, IR Grade Quartz, Calcium Fluoride, synthetic Sapphire etc.

Moreover, coatings can be applied to glass in order to enhance special properties such as thermal insulation, transmission, reflection, polarization, scratch-resistance and electrical resistance.These coatings include anti-reflection (AR) and optical coatings, metallic and transparent conductive coatings.

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OPTICAL GLASSES Typical Applications

To achieve the optimum image in an optical system, the main properties of optical glass must be considered. These properties include the refractive index, dispersion and transmission. Additional properties are fluorescence, solarisation and scintillation, which gain importance in optical glasses for special purposes. The above properties depend on the composition and homogeneity of the glass. In addition, the composition of the optical glass will affect the density and the coefficient of thermal expansion, which are key factors in material selection.

Optical glasses are used in the manufacture of components such as: > Beamsplitters > FS mirrors > Prisms > Light guides > Viewports > Precision spheres > Aspheric lenses > Crucibles > Domes

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Properties shown are typical values, they are not absolute material properties, and should be used for guidance only. It is recommended that materials and components are tested for their suitability for a specific application. For more information and advice please discuss your application with our sales staff.