Absorption Fluctuations and Persistent Spectral Hole burning in a Nd sup (3+) -doped Silica Glass Waveguide.

The observation of reproducible statistical absorption fluctuations of an inhomogeneously-broadened optical transition in a glass is reported. Frequency modulation spectroscopy in a 10ppm Nd sup (3+) -doped silica optical fiber has also revealed spectral holes which persist for days at 4.2K. Homogeneous linewidths GAMMA sub h measured using holeburning and fluctuations are in good mutual agreement but are are significantly larger than those inferred from photon echo decays in the same system. This difference confirms recent predictions of a time-dependent GAMMA sub h (t) arising from the tunneling dynamics of the glass.