Many ceramic materials, both glassy and crystalline, have found use as optically transparent materials in various forms: bulk solid-state components (phone glass), high surface area forms such as thin films, coatings, and fibers.
Ceramics have found widespread use for various applications in the electro-optical field including:
optical fibers for guided lightwave transmission
optical switches
laser amplifiers and lenses
hosts for solid-state lasers
optical window materials for gas lasers
infrared (IR) heat seeking devices for missile guidance systems
IR night vision.
Optical transparency in materials is limited by the amount of light that is scattered by their microstructural features with the amount of light scattering depending on the wavelength of the incident radiation, or light. For example, since visible light has a wavelength scale on the order of hundreds of nanometers, scattering centers will have dimensions on a similar spatial scale.
Most ceramic materials, such as those made of alumina, are formed from fine powders, yielding a fine grained polycrystalline microstructure filled with scattering centers comparable in size to the wavelength of visible light. Thus, they are generally opaque as opposed to transparent materials. In contrast, single-crystalline ceramics may be manufactured largely defect-free (particularly within the spatial scale of the incident light wave), offering nearly 99% optical transparency. Polycrystalline transparent ceramics based on alumina Al2O3, yttrium aluminium garnet (YAG), and neodymium-doped Nd:YAG were made possible by early 2000s nanoscale technology.
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