Abstract

The tunneling model [1] is the theoretical basis for several anomalous and time dependent phenomena in amorphous materials, which are caused by a broad distribution of relaxation rates of the so-called two-level systems (TLS). This model has also been applied to interpret spectral diffusion in glasses and to explain the observation of time dependent spectral linewidths [2]. In terms of spectral hole-burning, the TLS dynamics leads to a logarithmic hole broadening for times larger than the minimum TLS relaxation time, while the hole widths approach a constant value for times larger than the maximum TLS relaxation time [3]. This functional dependence is caused by a hyperbolic distribution of relaxation rates; all the above described phenomena follow from the “weak coupling” model: In polymer glasses a logarithmic broadening has been found on time scales between milliseconds and days [4, 5].

© 1994 Optical Society of America