Single-channel data rates could be more than 10 gigabits per second. Impurity ions at the various substitution sites have slightly different crystal-field environments, which results in small spectral shifts that are distinguishable at cryogenic temperatures.
Information is stored in the impurity ions by a mechanism called hole burning.
Relaxation of optically excited ions results in a nonstatistical redistribution of population among the nuclear-spin or hyperfine sublevels. Memory of the history of optical excitation is eventually lost through nuclear-spin relaxation, which may take as long as 24 hours, depending on the nature of the crystal host material and the storage temperature. The recorded information is recalled by a mechanism called the stimulated echo. Experimental Description Initial experiments used high power pulsed dye lasers. The write and read beams consisted of single short pulses.