  The best measurements of space and time currently possible (e.g.
gravitational wave detectors and optical reference cavities) rely on optical
resonators, and are ultimately limited by thermally induced fluctuations in the
reflective coatings which form the resonator. We present measurements of
coating thermal noise in the audio band and show that for a standard ion beam
sputtered coating, the power spectrum of the noise does not have the expected
power-law behavior.
