Free Induction Signals after Multipulse Excitation of a Spin System

A free induction signal (FIS) after excitation of a two-level inhomogeneously broadened spin system by a sequence of n electromagnetic pulses of the same duration t ₁ and with the same intervals between them is investigated theoretically and experimentally. It has been established that an FIS develops n coherent oscillations of magnetization, whose phases change in time following definite laws. These oscillations arise after cessation of the nth pulse and terminate successively at times that are multiple of t ₁, thus increasing the FIS duration. The conclusion has been drawn on the validity of the theorem of coherent transient processes on multipulse excitation of two-level spin systems with a finite inhomogeneous line width. The theoretical results are in fairly good agreement with the experimental data obtained in the NMR of protons in glycerin.