FEATURE OPTICAL COATINGS
The universal applications of optical coatings
From scanning spacetime to igniting nuclear fusion, the use cases for high- precision optical coatings are growing almost as fast as the techniques used to produce them, reports James Bakewell
O
ptical coatings are used to alter the way that a substrate transmits, reflects or polarises light. The surface of an uncoated
glass substrate, for example, will reflect about 4% of incident light, but an anti- reflection coating could be applied to reduce this to less than 0.1%. On the other hand, a highly reflective dielectric coating could be applied to increase the reflectivity of the glass to more than 99.99%. Today’s optical coatings are used in
numerous applications, from barcode scanners, which have anti-reflection coatings, to cameras on smartphones and optics used in high-power laser systems. Several markets for optical coatings have the potential for significant growth. Light detection and ranging (lidar)
systems, for instance, are being used to enable vehicles to sense the road in front of them and react appropriately, all without human input. Lidar systems use laser pulses for detection and ranging; and consist of a laser source acting as a transmitter, a photodetector acting as
22 Electro Optics February 2024
a receiver, and an assembly of lenses or optics to steer and collect the laser pulses. When the pulse encounters an object, it bounces back to the lidar unit, which then calculates the distance to the object based on the time elapsed between the emission of the pulse and the reception of the return beam. Computer algorithms use this information to determine the presence and shapes of cars, people and other obstacles. Lidar systems use infrared glass optics, such as those made from chalcogenides, which are difficult to coat, according to Professor Des Gibson, who is based at the University of the West of Scotland’s School of Computing, Engineering and Physical Sciences. He told Electro Optics: “These imaging systems are mounted on the front of cars and that’s a very harsh environment. So, you need high optical performance, but also very high durability.” Another growth market for optical
coatings is directed-energy weapons, according to James Oliver, the President of Vacuum Innovations. Directed energy weapons work by concentrating the high
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