LIGO Document P0900087-v1

Realization of a monolithic high-reflectivity cavity mirror from a single silicon crystal

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Cavity mirrors for laser radiation are essential as
heavy test masses of space-time for the new field of
gravitational wave astronomy, as mechanical oscillators
for targeting the quantum regime of macroscopic mechanical
devices, and for ultra-high-precision optical
clocks designed for researching the nature of fundamental
constants. Current limitations in all fields are set
by the joint problem of lacking appropriate cavity mirror
qualities. The currently used dielectrically coated mirrors
can show very high reflectivities but always at the
cost of a reduced mechanical quality, i.e. at the cost of
a thermal noise increase. Here we report on the first experimental realization of a high reflectivity surface mirror that solely consists of a single silicon crystal. Since no material was added to the crystal, the problem of ‘coating’ thermal noise is avoided. Our mirror is based on
a recently proposed surface nanostructure10 that creates
a resonant surface waveguide, and achieved a reflectivity
of (99.79±0.01)% and a cavity finesse of 2784 at a wavelength of 1.55 μm, in full agreement with a rigorous model. Perfect reflectivities of 100% are theoretically possible, and we anticipate that our achievement will open the avenue to new generations of a variety of experiments targeting fundamental questions of physics.
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