Spin-flip strategy

All these sequences include a (90°) preparation pulse which flips the magnetization of the spin system into the xy plane. The evolution period is then the period of free precession of the spin system in the xy plane, in the Hahn spin echo experiment (Fig. 6). The almost infinite variations in the mixing strategies serve the purpose of bringing out those features of the correlated motions in the system of coupled spins which one wishes to observe. 

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