Abstract
Amorphous silicon has ideal properties for many applications in fundamental research and industry. However, the optical absorption is often unacceptably high, particularly for gravitational-wave detection. We report a novel ion-beam deposition method for fabricating amorphous silicon with unprecedentedly low unpaired electron-spin density and optical absorption, the spin limit on absorption being surpassed for the first time. At low unpaired electron density, the absorption is no longer correlated with electron spins, but with the electronic mobility gap. Compared to standard ion-beam deposition, the absorption at 1550nm is lower by a factor of ≈100. This breakthrough shows that amorphous silicon could be exploited as an extreme performance optical coating in near-infrared applications, and it represents an important proof of concept for future gravitational-wave detectors.
Highlights
Introduction.—Highly reflective optical coatings have a wide range of applications in research and technology
We report a novel ion-beam deposition method for fabricating amorphous silicon with unprecedentedly low unpaired electron-spin density and optical absorption, the spin limit on absorption being surpassed for the first time
This breakthrough shows that amorphous silicon could be exploited as an extreme performance optical coating in near-infrared applications, and it represents an important proof of concept for future gravitational-wave detectors
Summary
Introduction.—Highly reflective optical coatings have a wide range of applications in research and technology. We report a novel ion-beam deposition method for fabricating amorphous silicon with unprecedentedly low unpaired electron-spin density and optical absorption, the spin limit on absorption being surpassed for the first time. To avoid heating and thermal deformation of the mirrors in gravitational-wave detectors, or to realize ultrahigh finesse cavities, low optical absorption at the ppm (10−6) level is required.
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