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Tenfold reduction of Brownian noise in high-reflectivity optical coatings


Thermally induced fluctuations impose a fundamental limit on precision measurement. In optical interferometry, the current bounds of stability and sensitivity are dictated by the excess mechanical damping of the high-reflectivity coatings that comprise the cavity end mirrors. Over the last decade, the dissipation of these amorphous multilayer reflectors has at best been reduced by a factor of two. Here, we demonstrate a new paradigm in optical coating technology based on direct-bonded monocrystalline multilayers, which exhibit both intrinsically low mechanical loss and high optical quality. Employing these ‘crystalline coatings’ as end mirrors in a Fabry–Pérot cavity, we obtain a finesse of 150,000. More importantly, at room temperature, we observe a thermally limited noise floor consistent with a tenfold reduction in mechanical damping when compared with the best dielectric multilayers. These results pave the way for the next generation of ultra-sensitive interferometers, as well as for new levels of laser stability.

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Figure 1: Design of the room-temperature 1,064 nm AlGaAs Bragg mirror.
Figure 2: Construction of an optical reference cavity using substrate-transferred crystalline coatings.
Figure 3: Details of the thermal noise measurement system.
Figure 4: Characterization of the crystalline-coating-stabilized 1,064 nm laser noise performance.


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The authors thank M.R. Abernathy, R.X. Adhikari, A. Alexandrovski, C. Benko, T. Chalermsongsak, G.M. Harry, R. Lalezari, L-S. Ma, E. Murphy, M. Notcutt, S.D. Penn, A. Peters, P. Ullmann and R. Yanka for discussions and technical assistance. Work at the University of Vienna is supported by the Austrian Science Fund (FWF), the European Commission and the European Research Council (ERC) Starting Grant Program. The work at CMS is supported by the Austria Wirtschaftsservice GmbH (AWS) and the ERC Proof of Concept Initiative. Work at JILA is supported by the US National Institute of Standards and Technology (NIST), the DARPA QuASAR Program, and the US National Science Foundation (NSF) Physics Frontier Center at JILA. Microfabrication was carried out at the Center for Micro- and Nanostructures (ZMNS) of the Vienna University of Technology.

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G.D.C. and M.A. designed the epitaxial multilayer, developed the substrate transfer process, and fabricated the bonded mirror assemblies. W.Z., M.J.M. and J.Y. designed and characterized the optical cavity, performed the laser frequency noise and stability measurements, and analysed the data. All authors contributed to writing the manuscript.

Corresponding authors

Correspondence to Garrett D. Cole or Jun Ye or Markus Aspelmeyer.

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Competing interests

G.D.C. and M.A. are co-founders of a startup company (Crystalline Mirror Solutions) and co-inventors on an international patent (European Application 11010091.4) focusing on the bonded mirror technology described in the Article.

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Cole, G., Zhang, W., Martin, M. et al. Tenfold reduction of Brownian noise in high-reflectivity optical coatings. Nature Photon 7, 644–650 (2013).

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