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

A detailed description is presented of photon echo experiments in Nd³⁺-doped silica optical fibers at temperatures below 1 K. Dephasing rates T₂^-1 have been obtained from two-pulse echo sequences at 0.89 {μ}m and are found to follow a T1.3 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.