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G. Wachter, St Kuhn, S. Minniberger, C. Salter, P. Asenbaum, J. Millen, M. Schneider, J. Schalko, U. Schmid, A. Felgner, D. Hüser, Mark. Arndt, M. Trupke:
"Silicon microcavity arrays with open access and a finesse of half a million";
Light-Science & Applications, 8 (2019), 37; S. 1 - 7.

Optical resonators are essential for fundamental science, applications in sensing and metrology, particle cooling, and
quantum information processing. Cavities can significantly enhance interactions between light and matter. For many
applications they perform this task best if the mode confinement is tight and the photon lifetime is long. Free access
to the mode center is important in the design to admit atoms, molecules, nanoparticles, or solids into the light field.
Here, we demonstrate how to machine microcavity arrays of extremely high quality in pristine silicon. Etched to an
almost perfect parabolic shape with a surface roughness on the level of 2 Å and coated to a finesse exceeding F =
500,000, these new devices can have lengths below 17 μm, confining the photons to 5 μm waists in a mode volume
of 88λ3. Extending the cavity length to 150 μm, on the order of the radius of curvature, in a symmetric mirror
configuration yields a waist smaller than 7 μm, with photon lifetimes exceeding 64 ns. Parallelized cleanroom
fabrication delivers an entire microcavity array in a single process. Photolithographic precision furthermore yields
alignment structures that result in mechanically robust, pre-aligned, symmetric microcavity arrays, representing a lightmatter
interface with unprecedented performance.

http://dx.doi.org/10.1038/s41377-019-0145-y