Definition: strongly curved optical windows
German: optische Kuppeln, Glaskuppeln
Author: Dr. Rüdiger Paschotta
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Optical domes are a special kind of optical windows, which are strongly curved. For example, they can have the shape of a half-sphere, but domes with custom shapes are also available. Different sizes are available, sometimes with diameters well above 100 mm.
Same optical domes need to transmit only visible light, for example for use with camera systems. They may be made of same high-quality optical glass like BK7 or fused silica. Glass domes are also available for the ultraviolet range, e.g. with UV-grade fused silica. For some applications, plastic optics (e.g. acrylic domes) are appropriate.
Other domes are operated in the infrared (→ infrared optics); for example, such devices are applied in heat-seeking missiles. A particularly robust infrared material is sapphire. Other possible choices, partly allowing for much longer wavelengths, are zinc selenide, germanium, silicon and certain ceramics.
A wide range of viewing directions is often important. The design of a half-sphere with the detector at its center may then be particularly appropriate because all light getting to these settings are will then have appropriately normal incidence on the dome surface. Under such conditions, there is no beam deflection, and anti-reflection coatings can reach a higher performance than for wide angular ranges.
Optical domes are mostly used for protecting sensitive systems. For example, optical sensors for LIDAR built into airplanes must be protected with quite robust domes, withstanding the impact of sand or even birds at high velocities. Similarly, domes for submarines and underwater camera and video systems must withstand high pressures.
Due to the priority of protective features, some compromises must be made concerning optical performance. The sometimes harsh operating conditions may anyway not make it possible to preserve a very high optical quality of the exterior surface.
For maximum robustness, some optical domes are equipped with diamond-like hard carbon coatings. There are also other coatings for optical domes, e.g. anti-reflection coatings with particularly high durability, infrared filter coatings and metalized coatings.
Some domes have special mechanical features for precise mounting and sealing.
The RP Photonics Buyer's Guide contains 17 suppliers for optical domes. Among them:
See also: optical windows, infrared optics
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