Requirements to impurity activated solids as materials for optical data storage and processing

Persistent spectral hole burning (PSHB) has remarkable applications in optical data storage and processing, including space-frequency and space-time domain holographies. Experiments have proven practically everything predicted and proposed by theory. The bottleneck between laboratory experiments and commercial applications is the need in low (liquid He) temperatures, as the main parameter of the data storage efficiency-the ratio between the inhomogeneous and homogeneous zero-phonon line (ZPL) widths α(T) = Γinh/Γhom(T)-- decreases owing to the rapid increase of Γhom(T) with temperature. A few optical and Mossbauer ZPLs are narrow even at RT, but they have usually also narrow Γinh. It is proposed to enlarge Γinh by making use of the Doppler effect. Two possible manifestations of the Doppler effect in the Universe are also discussed.