INSTANTANEOUS DIFFUSION IN SPIN-ECHO DYNAMICS - A FREQUENCY-DOMAIN EXPERIMENTAL INVESTIGATION

We report an experimental investigation on the spectral content of the echo radiation emitted by an electron spin system excited by a two-pulse sequence. The measurements are carried out at liquid-helium temperature in a sample of quartz containing a very low concentration of [AlO4]0 centers, in which instantaneous diffusion mechanism makes the main contribution to the phase relaxation. The experimental spectral shapes reproduce the theoretical ones, as calculated for an ideal system of noninteracting spins. However, the agreement is only qualitative, as the experimental spectral widths are found to be less than expected by a factor that depends on the exciting sequence and amounts up to 50%. On the basis of the observed features, this spectral narrowing effect is tentatively interpreted as a consequence of the phase relaxation induced by the instantaneous diffusion.