Material Properties

Low-Expansion Borosilicate Glass

The most well-known low-expansion borosilicate glass (LEBG) is Pyrex® made by Corning. It is well suited for applications in which high temperature, thermal shock, or resistance to chemical attack are primary considerations. On the other hand, LEBG is typically less homogeneous and contains more striae and bubbles than optical glasses such as BK7. This material is ideally suited to such tasks as mirror substrates, condenser lenses for high-power illumination systems, or windows in high-temperature environments. Because of its low cost and excellent thermal stability, it is the standard material used in test plates and optical flats. As seen in the figure below, transmission of LEBG extends into the ultraviolet and well into the infrared.

External transmittance for 8-mm-thick uncoated low-expansion borosilicate glass

The index of refraction in this material varies considerably from batch to batch. Typical values are shown in the accompanying table.

Refractive Index of Low- Expansion Borosilicate Glass Wavelength (nm) Refractive Index, n Fraunhofer Designation Source Spectral Region 486.1 1.479 F H2 arc Blue 514.5 1.477   Ar laser Green 546.1 1.476 e Hg arc Green 587.6 1.474 d Na arc Yellow 643.8 1.472 C' Cd arc Red

LOW-EXPANSION BOROSILICATE GLASS CONSTANTS Abbé Constant: vd = 66 Density: 2.23 g cm-3 at 25°C Young's Modulus: 5.98 x 109 dynes/mm2 Poisson's Ratio: 0.20 Specific Heat at 25°C: 0.17 cal/g°C Coefficient of Linear Expansion (0° to 300°C): 3.25 x 10-6/°C Softening Point: 820°C Melting Point: 1250°C Pyrex® is a registered trademark of Corning, Inc.

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Optics Guide Copyright 2002 Melles Griot Inc.