Optics

FIGURE 1. Right panel: Process Engineer Catherine Nguyen of Thorlabs holds the first produced 8-in. AlGaAs crystalline supermirror. Scaling the mirrors to large size is necessary to be used in gravitational wave detectors. The inset diagram shows the face-centered cubic zincblende structure of GaAs. In this depiction of a unit cell, gallium anions are blue and arsenic cations are red. In alternating layers of the coating, some of the gallium atoms are replaced by aluminum, resulting in the ternary alloy AlxGa1-xAs (AlGaAs) where x is the Al mole fraction, which has a lower refractive index than GaAs. Left panel: Schematic of the crystalline coating process. A GaAs/AlGaAs epitaxial Bragg mirror is grown on a base GaAs growth wafer, which is in turn directly bonded to the optical substrate (in this case comprising super-polished fused silica). Bonding is realized using a plasma-activated process, with a modest (<150°C) post-contact anneal. The GaAs growth wafer is then selectively removed via wet chemical etching, leaving the transferred epitaxial Bragg structure on the final optic.
Crystalline supermirrors are more than a specialized coating technology—by leveraging a semiconductor-enabled manufacturing process, they provide a path to lower noise for ever...
June 22, 2026

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