  Through the study of the power spectra of a monochromatic light beam
reflected by metallic mirrors, fluctuations in their reflectance is observed.
The power spectra were obtained down to a factor $10^{-6}$ below the Standard
Quantum Limit, with a dynamic range of $10^5$ in the frequency and power, using
methods we developed. The properties of the spectra are investigated and their
dependence on the material is analyzed. The physics underlying the phenomenon
is also discussed. These fluctuations provide a new window for investigating
the inner workings of materials.
