The next generation of large telescopes will require mirrors that are robust, highly reflective, uniform and have a base diameter greater than 8 meters.
Traditionally, evaporative coatings require wide source coverage and high deposition rates to effectively evaporate reflective coatings. In addition, special care must be taken to prevent evaporation of the chamfers, which can lead to the growth of columnar structures and reduced reflectivity.
Sputter coating is a unique technology that provides suitable solutions for single and multi-layer reflective coatings on large substrates. Long distance sputtering is a widely used semiconductor processing method and provides higher coating density and adhesion compared to sputtered coatings.
This technology creates uniform coverage along the entire curvature of the mirror and requires minimal masking. However, long-range aluminum sputtering has not yet found effective application in large telescopes. Short-throw atomization is another technology that requires advanced equipment capabilities and complex masks to compensate for mirror curvature.
This paper demonstrates a series of experiments to evaluate the effect of long-range spray parameters on mirror reflectivity compared to a conventional front-surface aluminum mirror.
Experimental results show that water vapor control is a major factor in creating durable and highly reflective aluminum mirror coatings, and also show that long-distance spraying under low water pressure conditions can be very effective.
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Post time: Sep-28-2023