Optical dephasing by tunneling systems in glass.

A description of optical dephasing in inorganic glasses is presented which implicates low-energy atomic tunneling systems as the dominant contributor below 1K. Photon echoes have shown that the dephasing rate of Nd(3+) in pure SiO2 varies with temperature as T(1.3) between 0.1 and 1K. The behavior of the photon echoes and of the dephasing rate is quantitatively interpreted in terms of a spectral diffusion process which originates in the elastic dipolar coupling between active ions and tunneling centers.