SPECTRAL INVESTIGATION OF SPIN-ECHO EMISSION

The spectral content of the echo radiation emitted after a two-pulse s equence is measured in a two-level spin system. The spectral profiles exhibit maxima and zeroes of spectral density depending on the excitin g sequence parameters. A calculation based on a vectorial model relate s the zeroes to those packets that happen to be transparent to the sec ond (refocusing) pulse. Moreover we report on a new spectral narrowing effect which we tentatively ascribe to the instantaneous diffusion.