Low temperature optical dephasing of rare earth ions in inorganic glasses.

A detailed description is presented of phonton echo experiments in Nd(3+ doped silica optical fibers at temperatures below 1K. Dephasing rates T-1 over 2 have been obtained from two pulse echo sequences at 0.89micron and are found to follow a T(1.3) temperature dependence. An interpretation of this result is presented which invokes the interaction of tunneling systems with the optical ions via a dipole-dipole elastic interaction. The dynamics of the interaction originates in a spectral diffusion process and three pulse stimulated echo experiments confirm this interpretation.