Optical Materials
Optical components such as lenses, prisms, mirrors, spherical lenses, and diffraction gratings are all made from various optical materials. The quality of optical materials directly affects the imaging quality and performance of optical components and systems. Optical materials need to meet the requirement that refractive materials have good transmittance in the operating wavelength range, and reflective components have high reflectance in the operating wavelength range.
I. Optical Characteristics of Transmissive Materials
Transmissive materials are mainly divided into three categories: optical glass, optical crystals, and optical plastics. Their optical characteristics are mainly determined by their transmittance to various colors of light.
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Optical Glass: Optical glass is a commonly used optical material with mature manufacturing processes and a wide range of varieties. Typical optical glass can transmit various colors of light with wavelengths ranging from 0.35 to 2.5 micrometers, but light beyond this range is strongly absorbed by optical glass. Optical glass is divided into crown glass and flint glass, each with different dispersion and refractive index characteristics.
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Optical Plastics: Optical plastics are lightweight, have good plasticity, and strong impact resistance, making them easy to process into shapes. Although the cost of plastic molds is high, mass production can reduce costs. Optical plastics are widely used in optical systems, but their transmittance is relatively poor compared to glass, and their thermal stability and chemical stability are not as good.
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Optical Crystals: Optical crystals have good transmittance and low dispersion, suitable for ultraviolet, visible, and infrared bands. In the ultraviolet and infrared bands, optical crystals are widely used and play a role in acousto-optics, electro-optics, magneto-optics, and lasers.
The refractive characteristics of transmissive materials are generally represented by the refractive index of the Fraunhofer lines. They are divided into crown glass and flint glass according to their refractive index and Abbe number.
II. Optical Characteristics of Reflective Materials
Reflective optical elements are made by depositing thin films of highly reflective metallic materials on polished glass or metal surfaces. The optical characteristics of reflective optical materials are the reflectance to various colors of light and are not affected by dispersion. The reflectance of different metal coatings varies, and the reflectance of the same metal material varies with wavelength.
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