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Material Properties

Optical Crown Glass

In optical crown glass, a low-index commercial-grade glass, the index of refraction, transmittance, and homogeneity are not controlled as carefully as they are in optical-grade glasses such as BK7. Optical crown is suitable for applications in which component tolerances are fairly loose and as a substrate material for mirrors.

Transmittance characteristics for optical crown are shown the figure below. Relevant properties of optical crown are shown in the accompanying table.
Optics Figure
External transmittance for 10-mm-thick uncoated optical crown glass

 
Optical Crown Glass Constants
Glass Type Designation: B270
Abbé Constant: vd = 58.5
Dispersion: (nF - nC) = 0.0089
Density: 2.55 g-cm-3 at 23°C
Young's Modulus: 71.5 kN/mm2
Specific Heat: Cp (20° to 100°C) = 0.184 cal/g-°C
Coefficient of Linear Expansion (20° to 300°C): 93.3 x 10-7/°C
Transformation Temperature: 521°C
Softening Point: 708°C

Refractive Index of Optical Crown Glass
Wavelength
(nm)		 Refractive
Index, n		 Fraunhofer
Designation		 Source Spectral
Region
435.8 1.53394 g Hg arc Blue
480.0 1.52960 F' Cd arc Blue
486.1 1.52908 F H2 arc Blue
546.1 1.52501 e Hg arc Green
587.6 1.52288 d He arc Yellow
589.0 1.52280 D Na arc Yellow
643.8 1.52059 C' Cd arc Red
656.3 1.52015 C H2 arc Red

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Optics Guide Copyright 2002 Melles Griot Inc.